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15 Jun 1997

Volume 81, Issue 12, pp. 7709-8123

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Eigenfrequencies of a rectangular atomic force microscope cantilever in a medium

Franz-Josef Elmer and Markus Dreier

J. Appl. Phys. 81, 7709 (1997); http://dx.doi.org/10.1063/1.365379 (6 pages) | Cited 43 times

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We calculate the eigenfrequencies of a rectangular cantilever of an atomic force microscope immersed in a fluid or a gas. To do so, the problem of combined elastomechanical and hydrodynamical equations is solved approximatively. The results are compared with experimentally obtained frequencies. For water the difference between experiment and theory is less than 4% if the ratio of the height of the cantilever to the width is less than 1/20 and if the corresponding eigenmode has at least four nodes. © 1997 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
07.79.Lh Atomic force microscopes
68.35.B- Structure of clean surfaces (and surface reconstruction)

Electron attachment to excited states of silane: Implications for plasma processing discharges

Lal A. Pinnaduwage and Panos G. Datskos

J. Appl. Phys. 81, 7715 (1997); http://dx.doi.org/10.1063/1.365381 (13 pages) | Cited 23 times

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Observation of enhanced negative-ion formation in ArF–excimer–laser irradiated silane was reported in a recent paper [L. A. Pinnaduwage, M. Z. Martin, and L. G. Christophorou, Appl. Phys. Lett. 65, 2571 (1994)]. In that paper, preliminary evidence was presented to show that highly excited electronic states of silane or its photofragments could be responsible for the observed enhanced negative-ion formation. In the present paper, we report evidence, obtained using a new experimental technique, that the electron attaching species are high-Rydberg (HR) states of silane indirectly populated via laser irradiation and show that an absolute lower bound for the corresponding electron attachment rate constant is ∼ 4×10−7 cm3 s−1. The initial capture of the electron by the HR states is likely to be a diabatic process and the large polarizabilities associated with the HR states appear to be responsible for the observed large electron attachment rate constants. We also measured electron attachment to thermally excited vibrational states of the ground electronic state of silane, which showed no measurable electron attachment up to 750 K. Implications of these observations in modeling of silane discharges used for plasma processing of amorphous silicon are discussed. It is also pointed out that large negative ion formation observed in many “weakly electronegative” plasma processing gas discharges could be due to enhanced electron attachment to HR states: such states could be populated via direct electron impact and/or via excitation transfer from the metastable states of rare gases that are commonly used in these processing discharges. © 1997 American Institute of Physics.
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34.80.Lx Recombination, attachment, and positronium formation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
31.50.Df Potential energy surfaces for excited electronic states
52.80.-s Electric discharges
33.15.Mt Rotation, vibration, and vibration-rotation constants

Nonlinear self-defocusing in doped silica sono-gels

Rocío Ramos, Paul Michael Petersen, Per Michael Johansen, Lars Lindvold, Mila Ramírez, and Eduardo Blanco

J. Appl. Phys. 81, 7728 (1997); http://dx.doi.org/10.1063/1.365551 (6 pages) | Cited 5 times

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Experiments with nonlinear self-refraction of Gaussian laser beams in silica sono-gels doped with copper tetrasulfonated phthalocyanine are reported. The propagation of laser beams inside nonlinear sol-gel samples with different Cu-phthalocyanine concentrations has been monitored by measuring the spatial beam profile in the near field and in the far field behind the sample. The experimental results are analyzed by a new simple theoretical approach, in which we assume that the incident Gaussian beam induces a phase shift that varies as a Gaussian function of the beam radius. The beam propagation behind the sample is determined by the Huygens–Fresnel integral formalism. By solving the Huygens–Fresnel integral, analytical expressions for the spatial beam profile in both the near field and the far field after the nonlinear sample are obtained. Experiments are carried out with a diode pumped frequency doubled Nd–YAG laser at 532 nm. We obtain very large third-order nonlinearities in these doped sol-gel samples at temperatures just above room temperature. When we compare the predictions of the theory with the experimental data, we find experimental values of the nonlinear third-order susceptibility up to −2.3×10−4 esu. © 1997 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.An Optical susceptibility, hyperpolarizability
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
82.70.Gg Gels and sols

Study on the ions’ behavior in an electron cyclotron resonance plasma

Minghai Liu, Xiwei Hu, and Hanming Wu

J. Appl. Phys. 81, 7734 (1997); http://dx.doi.org/10.1063/1.365382 (5 pages) | Cited 10 times

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The energy, velocity, angle distribution of ions in magnetoactive electron cyclotron resonance plasma have been studied with a two-dimension hybrid mode. The dependence of these distribution functions versus position and pressure are discussed. Our simulation results are in good agreement with many experimental measurements. © 1997 American Institute of Physics.
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52.25.-b Plasma properties
52.25.Fi Transport properties
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Influence of the microstructure on the macroscopic elastic and optical properties of dried sonogels: A Brillouin spectroscopic study

R. J. Jiménez-Riobóo, M. García-Hernández, C. Prieto, J. J. Fuentes-Gallego, E. Blanco, and M. Ramírez-del-Solar

J. Appl. Phys. 81, 7739 (1997); http://dx.doi.org/10.1063/1.365383 (7 pages) | Cited 16 times

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The elastic and optical properties of organically modified silicates prepared by ultrasonics aided polycondensation of tetraethoxysilane and polidimethylsiloxane are studied by means of high resolution Brillouin spectroscopy. Nuclear magnetic resonance data evidence the microseparation of the organic and inorganic phases for the systems with high content of polymer formation. The elastic and optical properties are clearly influenced by the change in microstructure. We propose a three component mechanical model that qualitatively explains the observed variation of the elastic constant c11 versus molar fraction of dimethylsiloxane in these vitreous materials and develop a structural model that accounts for the observed dynamical behavior. © 1997 American Institute of Physics.  
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81.40.Jj Elasticity and anelasticity, stress-strain relations
82.70.Gg Gels and sols
61.43.-j Disordered solids
62.20.D- Elasticity
78.35.+c Brillouin and Rayleigh scattering; other light scattering
76.60.-k Nuclear magnetic resonance and relaxation
61.41.+e Polymers, elastomers, and plastics

Passivation effect of silicon nitride against copper diffusion

Hiroshi Miyazaki, Hisao Kojima, and Kenji Hinode

J. Appl. Phys. 81, 7746 (1997); http://dx.doi.org/10.1063/1.365380 (5 pages) | Cited 19 times

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The use of Cu in ultralarge scale integrated (ULSI) conductors has resulted in the need to prevent Cu diffusion. We evaluated the passivation effect of plasma-enhanced chemical-vapor-deposited silicon nitride (PECVD-SiN) using secondary ion mass spectrometry and atomic absorption spectrometry. From these measurements, it was found that a large amount of Cu diffused through PECVD-SiN films during the heat treatments of the metallization process, probably due to the rapid diffusion paths along the microdefects of PECVD-SiN films. However, Cu contamination was barely detected in the current–voltage measurements and bias-temperature stressing tests of Cu/PECVD-SiN/SiO2/Si capacitors because the leakage current through SiN films slightly increased as a result of Cu diffusion. This result is attributed to the electric-field relaxation caused by a large number of electrons trapped in the PECVD-SiN films, of which the negative charge compensates the positive charge of Cu ions. Although the degradation of electrical characteristics is not explicitly observed in simulation using Cu/PECVD-SiN/SiO2/Si capacitors, Cu atoms reach Si devices in the actual process. Therefore, the passivation effect of PECVD-SiN films is insufficient to allow application to ULSI devices. © 1997 American Institute of Physics.
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81.65.Rv Passivation
81.05.Cy Elemental semiconductors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Fx Diffusion; interface formation
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Impression creep of a viscous fluid

Fuqian Yang, Xiaoyi He, M. Dembo, and J. C. M. Li

J. Appl. Phys. 81, 7751 (1997); http://dx.doi.org/10.1063/1.365384 (6 pages) | Cited 2 times

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The impression test of a Newtonian fluid under a constant load and for a small Reynolds number flow was simulated by using the finite element method. It is found that the penetration velocity is a constant if the surface tension/viscosity ratio is less than 0.1 cm/s, the product of surface tension and indenter radius is less than 0.05 of the applied load, and the penetration depth is less than 1/3 of the indenter radius. Such constant penetration velocity is proportional to the applied load and inversely proportional to the viscosity and the indenter radius. The stick or slip boundary condition at the interface between the indenter and the fluid has no effect on the penetration velocity under these conditions. © 1997 American Institute of Physics.
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62.10.+s Mechanical properties of liquids
83.10.Gr Constitutive relations
68.03.Cd Surface tension and related phenomena
66.20.-d Viscosity of liquids; diffusive momentum transport
68.03.-g Gas-liquid and vacuum-liquid interfaces

Dendritic crystallization of amorphous germanium by in situ thermal pulse annealing

K. M. Lui, K. P. Chik, and J. B. Xu

J. Appl. Phys. 81, 7757 (1997); http://dx.doi.org/10.1063/1.365385 (7 pages) | Cited 3 times

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Phase transformation of amorphous-germanium thin film has been carried out on amorphous substrate by in situ thermal-pulse annealing in a high vacuum chamber directly after evaporation. The microstructure of the resultant film was shown to depend markedly both on the annealing ambient and on the time of exposure (te) for the as-deposited films under full-powered (<102 W/cm2) incoherent broadband irradiation. The heating rate was estimated to be not less than 102 K/s. The surface morphology of the sample was examined by atomic force microscopy (AFM), scanning electron microscopy, and optical microscopy. For samples annealed in air, hillock growth mode was observed, while for samples annealed in vacuum, a transition from the microgranular to dendritic grain growth, depending sensitively on te, was clearly evident. Surprisingly, the length of the crystallized dendrites could be as long as ≃ 104 μm, being at least ≃ 104 times larger than the thickness of the film. The dendritic morphology, the implied growth rate, and the condition of crystallization lead us to suggest that the Ge film may exist in a supercooled semiconductive liquid phase just before crystallization. X-ray diffraction analysis revealed that grains were crystallized dominantly with a random orientation for te<2.84±0.05 s, while a sharp transition to a preferred 〈110〉 crystal orientation occurred at the critical te of 3.22±0.05 s, corresponding to a maximum temperature (Tm) of 577 °C reached by the system. This transition is consistent with the appearance of dendrites in AFM micrographs. More interestingly, an anomalous lateral size effect of the substrate on the misalignment of the 〈110〉 crystal direction of different grains with respect to the substrate normal was observed from the x-ray rocking curves. Careful inspection of the AFM images found that the giant dendrites broke up into individual columnar grains as the substrate width went down in size. © 1997 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
68.55.-a Thin film structure and morphology
64.70.K- Solid-solid transitions
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)

Structural, electrical and optical properties of aluminum doped zinc oxide films prepared by radio frequency magnetron sputtering

Kun Ho Kim, Ki Cheol Park, and Dae Young Ma

J. Appl. Phys. 81, 7764 (1997); http://dx.doi.org/10.1063/1.365556 (9 pages) | Cited 179 times

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Aluminum doped zinc oxide (AZO) films are prepared by rf magnetron sputtering on glass or Si substrates using specifically designed ZnO targets containing different amount of Al2O3 powder as the Al doping source. The structural, electrical, and optical properties of the AZO films are investigated in terms of the preparation conditions, such as the Al2O3 content in the target, rf power, substrate temperature and working pressure. The crystal structure of the AZO films is hexagonal wurtzite. The orientation, regardless of the Al content, is along the c axis perpendicular to the substrate. The doping concentration in the film is 1.9 at. % for 1 wt % Al2O3 target, 4.0 at. % for 3 wt % Al2O3 target, and 6.2 at. % for 5 wt % Al2O3 target. The resistivity of the AZO film prepared with the 3 wt % Al2O3target is ∼ 4.7×10−4 Ω cm, and depends mainly on the carrier concentration. The optical transmittance of a 1500-Å-thick film at 550 nm is ∼ 90%. The optical band gap depends on the Al doping level and on the microstructure of the films, and is in the range of 3.46–3.54 eV. The optical band gap widening is proportional to the one-third power of the carrier concentration. © 1997 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
42.79.Wc Optical coatings
73.61.Ga II-VI semiconductors

Texture and stress of Ag films in Ag/Ti, Ag/Cr bilayers, and self-encapsulated structures

Yuxiao Zeng, Y. L. Zou, T. L. Alford, F. Deng, S. S. Lau, T. Laursen, and B. Manfred Ullrich

J. Appl. Phys. 81, 7773 (1997); http://dx.doi.org/10.1063/1.365386 (5 pages) | Cited 13 times

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The texture of evaporated Ag films prepared on Ti or Cr underlayers before and after encapsulation process has been studied by x-ray diffraction. In addition, the stress state in self-encapsulated Ag/Ti structures has also been investigated using a “sin2 ψ” technique. Silver films deposited on Ti layers exhibit a strong 〈111〉 texture, which is in contrast to the nearly random orientation of Ag films on Cr underlayers. The minimization of interfacial energy with respect to lattice match can account for this underlayer dependence. After an encapsulation process involving Ti reactions in an ammonia ambient, the texture of Ag films in Ag/Ti bilayers is further enhanced. Highly textured Ag films may provide the basis for electromigration-resistant Ag metallization in integrated circuit devices. For the Ag/Ti bilayer structures, a low tensile stress of approximately 61 MPa arising from the nonequilibrium growth during the film deposition is present in the Ag films. This results in a lattice tension state in the film plane and a lattice compression state along the film normal. Thermal mismatch stress is produced by the encapsulation process at 600 °C. Most of this stress relaxes during the cooling stage and a residual tensile stress of ∼320 MPa in the film plane was determined. © 1997 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Gy Mechanical properties; surface strains
81.05.Bx Metals, semimetals, and alloys
68.35.Md Surface thermodynamics, surface energies
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

Heterostructures in GaInP grown using a change in V/III ratio

Y. S. Chun, H. Murata, S. H. Lee, I. H. Ho, T. C. Hsu, G. B. Stringfellow, C. E. Inglefield, M. C. DeLong, P. C. Taylor, J. H. Kim, and T.-Y. Seong

J. Appl. Phys. 81, 7778 (1997); http://dx.doi.org/10.1063/1.365387 (9 pages) | Cited 4 times

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A natural monolayer {111} superlattice (the CuPt ordered structure) is formed spontaneously during organometallic vapor phase epitaxial (OMVPE) growth of Ga0.52In0.48P. The extent of this ordering process is found to be a strong function of the input partial pressure of the phosphorus precursor during growth due to the effect of this parameter on the surface reconstruction and step structure. Thus, heterostructures can be produced by simply changing the flow rate of the P precursor during growth. It is found, by examination of transmission electron microscope (TEM) and atomic force microscope (AFM) images, and the photoluminescence (PL) and PL excitation (PLE) spectra, that order/disorder (O/D) (really less ordered on more ordered) heterostructures formed by decreasing the partial pressure of the P precursor during the OMVPE growth cycle at a temperature of 620 °C are graded over several thousands of Å when PH3 is the precursor. The ordered structure from the lower layer persists into the upper layer. Similarly, D/O structures produced by increasing the PH3 flow rate yield PL spectra also indicative of a graded composition at the heterostructure. The grading is not reduced by a 1 h interruption in the growth cycle at the interface. Similar heterostructures produced at 670 °C using tertiarybutylphosphine (TBP) as the P precursor show a totally different behavior. Abrupt D/O and O/D heterostructures can be produced by abruptly changing the TBP flow rate during the growth cycle. PL and PLE studies show distinct peaks closely corresponding to those observed for the corresponding single layers. TEM dark field images also indicate that the interfaces in both for D/O and O/D heterostructures are abrupt. The cause of the difference in behavior for TBP and PH3 is not clear. It may be related to the difference in temperature. © 1997 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Lateral structure of (TiSe2)n(NbSe2)m superlattices

Myungkeun Noh, Hyun-Joon Shin, Kwangho Jeong, Jennifer Spear, David C. Johnson, Stephen D. Kevan, and Tony Warwick

J. Appl. Phys. 81, 7787 (1997); http://dx.doi.org/10.1063/1.365388 (6 pages) | Cited 3 times

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The structures of a series of (TiSe2)n(NbSe2)m superlattices grown through controlled crystallization of designed multilayer reactants have been studied. X-ray diffraction of the data of the superlattices after crystallization show considerable preferred orientation, with the basal plane of the dichalcogenide structure parallel to the substrate to within 0.1°. Lattice refinement using the observed (00l) diffraction maxima yields lattice parameters along the c axis that are consistent with those expected based on the target superlattices and lattice parameters of the binary constituents. These (00l) diffraction data, however, contain no information about the crystalline structure in the ab plane of the superlattice associated with the preferred c-axis orientation. Off-specular x-ray diffraction (XRD), scanning electron microscopy, and scanning transmission x-ray microscopy (STXM) were used to explore the structure and homogeneity of the superlattices in the ab plane. XRD results rule out preferred long-range orientational order of the ab plane. Between grains, both the backscattered electron images and STXM images show grain domain structure in the ab plane with a characteristic grain domain size of approximately 50 μm. X-ray absorption microscopy in the STXM mode obtained at the Ti L2,3 edge shows that the titanium in the superlattices is present as both octahedral Ti consistent with the TiSe2 structure and metallic Ti. A comparison of the data obtained from these techniques highlights chemical information, which can be deduced on a submicrometer range from the space resolved spectra obtained using STXM. © 1997 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.30.Dz Phase diagrams of other materials

Interfacial interaction between Al-1%Si and phosphorus-doped hydrogenated amorphous Si alloy at low temperature

Wen-Shiang Liao and Si-Chen Lee

J. Appl. Phys. 81, 7793 (1997); http://dx.doi.org/10.1063/1.365389 (5 pages) | Cited 2 times

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The interfacial interaction between phosphorus-doped amorphous silicon hydrogen alloy ((n+)a-Si:H) and thermal evaporated Al-1%Si layer after furnace annealing in the temperature range from 150 to 250 °C has been investigated in detail. The scanning electron microscope photographs show that many dendrites were formed on the original (n+)a-Si:H surface at annealing temperature higher than 170 °C. Raman spectroscopy and transmission electron diffraction show that the original (n+)a-Si:H film has been converted to polycrystalline Si with the crystalline Si dendrites on top. The drastic increase ( ∼ 4 orders of magnitude) of electrical conductivity of the 200 °C annealed (n+)a-Si:H films with the Al-1%Si removed is caused by the formation of polycrystalline silicon percolation channel in the background area between dendrites. Auger spectroscopy also provides evidence that no aluminum is incorporated into the converted film during silicon recrystallization and thus no SiAl alloy is formed. © 1997 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
72.80.Cw Elemental semiconductors
72.80.Ng Disordered solids
73.61.Jc Amorphous semiconductors; glasses
73.61.Cw Elemental semiconductors
81.40.Gh Other heat and thermomechanical treatments
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
78.66.Jg Amorphous semiconductors; glasses

Structural stability of hydrogenated (100) surface of cubic boron nitride in comparison with diamond

Shojiro Komatsu, Walter Yarbrough, and Yusuke Moriyoshi

J. Appl. Phys. 81, 7798 (1997); http://dx.doi.org/10.1063/1.365376 (8 pages) | Cited 9 times

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In view of (1×1):2H dihydride/(2×1):H monohydride reconstruction, structural stability of (100) surfaces of both cBN and diamond was comparatively investigated by semiempirical molecular orbital methods using isoelectronic clusters of B52N42H80−2n(10−), N52B42H80−2n(10+), and C94H80−2n, to model (100)B and (100)N of cBN, and diamond surface, respectively, where n = 0, 1, 2, or 3. The n denotes the number of monohydride dimers formed. These clusters were nanometer-sized pyramidal crystallites bound by four of {111} faces and one (100). The (100)N of cBN was found unique because of the great stability as (1×1):2H dihydride phase, which retains the bulk structure truncated at the surface without reconstruction and is expected to be chemically inert. This passivation seems to be related to the difficulty in chemical vapor deposition of high quality cBN. The (100)B of cBN was predicted to stabilize as (2×1):H monohydride phase as much as hydrogenated (100) of diamond does. © 1997 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena

Partial density of states in the CuInSe2  valence bands

T. Löher, A. Klein, C. Pettenkofer, and W. Jaegermann

J. Appl. Phys. 81, 7806 (1997); http://dx.doi.org/10.1063/1.365390 (4 pages) | Cited 9 times

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The valence band spectra of a vacuum cleaved CuInSe2 (011) surface were measured with synchrotron radiation at photon energies between 16 and 95 eV. The strong dependence of the photoionization cross section of atomic levels between 28 and 60 eV is used to divide the valence band emissions into contributions from Se 4p and Cu 3d states in order to map the respective partial density of states. The derived partial density of Cu 3d states to the total valence band density of states is around 50% in the upper part of the valence band and about 75% at its maximum corresponding to non-bonding Cu d states. © 1997 American Institute of Physics.
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71.20.Nr Semiconductor compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Hole mobilities and the effective Hall factor in p-type GaAs

M. Wenzel, G. Irmer, J. Monecke, and W. Siegel

J. Appl. Phys. 81, 7810 (1997); http://dx.doi.org/10.1063/1.365391 (7 pages) | Cited 6 times

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We prove the effective Hall factor in p-GaAs to be larger than values discussed in the literature up to now. The scattering rates for the relevant scattering mechanisms in p-GaAs have been recalculated after critical testing the existing models. These calculations allow to deduce theoretical drift and theoretical Hall mobilities as functions of temperature which can be compared with measured data. Theoretical Hall factors in the heavy and light hole bands and an effective Hall factor result. The calculated room temperature values of the drift mobility and of the effective Hall factor are 118 cm2/V s and 3.6, respectively. The fitted acoustic deformation potential E1 = 7.9 eV and the fitted optical coupling constant DK = 1.24×1011 eV/m are close to values published before. It is shown that the measured strong dependence of the Hall mobility on the Hall concentration is not mainly caused by scattering by ionized impurities but by the dependence of the effective Hall factor on the hole concentration. © 1997 American Institute of Physics.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Ey III-V and II-VI semiconductors
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Transient thermoelectric effect with tunable pulsed laser: Experiment and computer simulations for p-GaAs

Minoru Sasaki, Tomoh Ueda, Makoto Tanioka, Hirokazu Mukai, and Masasi Inoue

J. Appl. Phys. 81, 7817 (1997); http://dx.doi.org/10.1063/1.365192 (10 pages) | Cited 4 times

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A photoinduced “transient thermoelectric effect” (TTE) has been measured for a p-GaAs crystal using a tunable pulsed laser, over the laser energy range 0.93–1.80 eV, laser intensity 0.2–130 mJ/cm2, time range 1 ns–1 ms, and temperature range 4.2–50 K, with special attention to native defects of EL2 centers, whose ground state (EL20) and excited state (EL2ex) are located, respectively, at 0.76 and 1.80 eV above the top of the valence band (their energy difference σex = 1.04 eV). After laser irradiation at one end of the sample, a TTE voltage is induced within a rising time τr (1.0–1.5 μs) due to hole diffusion, followed by exponential decay with multiple decay times τ1–τ5 that depend on the laser energy, its intensity, and the temperature. The decay time τ1 is assigned to relate to photoexcited electron diffusion in the conduction band and others τ2–τ5 with electron recombinations with photogenerated holes in the valence band via EL2 centers in p-GaAs, for which a rough evaluation of the capture cross section is made. Based on the experimental data, we have discussed the photoinduced carrier generation/recombination processes in three laser energy ranges with the two boundaries σex and the band-gap energy Eg (=1.50 eV); regions I (E<σex), II (σex ⩽ E<Eg), and III (E ≥ Eg). For these three energy regions, we have carried out computer simulations for the photoinduced TTE voltage profiles by solving one-dimensional transport equations for photogenerated electrons and holes, in qualitative agreement with the observations. © 1997 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
72.20.Pa Thermoelectric and thermomagnetic effects
72.40.+w Photoconduction and photovoltaic effects
71.55.Eq III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Theory of hole initiated impact ionization in bulk zincblende and wurtzite GaN

Ismail H. Oğuzman, Enrico Bellotti, Kevin F. Brennan, Ján Kolník, Rongping Wang, and P. Paul Ruden

J. Appl. Phys. 81, 7827 (1997); http://dx.doi.org/10.1063/1.365392 (8 pages) | Cited 50 times

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In this article, the first calculations of hole initiated interband impact ionization in bulk zincblende and wurtzite phase GaN are presented. The calculations are made using an ensemble Monte Carlo simulation including the full details of all of the relevant valence bands, derived from an empirical pseudopotential approach, for each crystal type. The model also includes numerically generated hole initiated impact ionization transition rates, calculated based on the pseudopotential band structure. The calculations predict that both the average hole energies and ionization coefficients are substantially higher in the zincblende phase than in the wurtzite phase. This difference is attributed to the higher valence band effective masses and equivalently higher effective density of states found in the wurtzite polytype. Furthermore, the hole ionization coefficient is found to be comparable to the previously calculated electron ionization coefficient in zincblende GaN at an applied electric field strength of 3 MV/cm. In the wurtzite phase, the electron and hole impact ionization coefficients are predicted to be similar at high electric fields, but at lower fields, the hole ionization rate appears to be greater. © 1997 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
72.80.Ey III-V and II-VI semiconductors
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.20.Nr Semiconductor compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
02.70.Rr General statistical methods

Origin of the increase in resistivity of manganese–zinc ferrite polycrystals with oxygen partial pressure

Soon Cheon Byeon, Kug Sun Hong, Jae Gwan Park, and Won Nam Kang

J. Appl. Phys. 81, 7835 (1997); http://dx.doi.org/10.1063/1.365393 (7 pages) | Cited 15 times

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In our present study, the origin of the increase in resistivity of polycrystalline Mn0.47Zn0.47Fe2.06O4 with increasing oxygen partial pressure was investigated by measuring thermoelectric power and electrical resistivity, and through analysis of grain size. The ferrous ion (Fe2+) concentration of the samples was estimated using the thermoelectric power data and it indicated that the increase of oxygen partial pressure accompanied only a 0.5 wt. % decrease in the concentration of Fe2+. The decrease in Fe2+ concentration failed to explain the order of magnitude increase in resistivity. Preferential oxidation of the grain boundaries did not contribute to the increase in resistivity since all the samples were cooled under the same conditions, i.e., constant oxidation potential. Impedance spectroscopy revealed that the increase in resistivity arose from the increase in resistivity of the grain boundary; this is discussed in terms of the microscopic shape factor, the brick-layer model, and the Maxwell–Wagner model. It is suggested that the increase in resistivity, with increasing oxygen partial pressure, originates from the increase in the microscopic shape factor of the grain boundary. © 1997 American Institute of Physics.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Pa Thermoelectric and thermomagnetic effects
61.72.Mm Grain and twin boundaries
75.50.Gg Ferrimagnetics

n-Type conduction in Pb doped Se–In chalcogenide glasses

R. M. Mehra, Sandeep Kohli, Amit Pundir, V. K. Sachdev, and P. C. Mathur

J. Appl. Phys. 81, 7842 (1997); http://dx.doi.org/10.1063/1.365397 (3 pages) | Cited 16 times

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This paper reports on the p to n transition in Pb doped Se–In chalcogenide glasses. Measurements of thermoelectric power in the temperature range 300 K ⩽ T ⩽ 315 K, dc conductivity in the temperature range 100 ⩽ T ⩽ 300 K, and optical band gap (Egopt) have been carried out for Se75In25−xPbx (x = 0,5,10,15) samples. The p-n transition occurs with very low addition of Pb impurity (5 at. %). The conductivity and pre-exponential factor also change by five to six orders of magnitude with Pb doping. Results are explained on the basis of the formation of ionic Pb–Se bonds, instead of covalent bonds. Formation of ionic bonds disturbs the equilibrium between the charged defect states of Se–In glass and unpins the Fermi level and thus leads to n-type conduction in these glasses. © 1997 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
72.80.Ng Disordered solids
72.20.Pa Thermoelectric and thermomagnetic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Single and multiband modeling of quantum electron transport through layered semiconductor devices

Roger Lake, Gerhard Klimeck, R. Chris Bowen, and Dejan Jovanovic

J. Appl. Phys. 81, 7845 (1997); http://dx.doi.org/10.1063/1.365394 (25 pages) | Cited 275 times

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Non-equilibrium Green function theory is formulated to meet the three main challenges of high bias quantum device modeling: self-consistent charging, incoherent and inelastic scattering, and band structure. The theory is written in a general localized orbital basis using the example of the zinc blende lattice. A Dyson equation treatment of the open system boundaries results in a tunneling formula with a generalized Fisher-Lee form for the transmission coefficient that treats injection from emitter continuum states and emitter quasi-bound states on an equal footing. Scattering is then included. Self-energies which include the effects of polar optical phonons, acoustic phonons, alloy fluctuations, interface roughness, and ionized dopants are derived. Interface roughness is modeled as a layer of alloy in which the cations of a given type cluster into islands. Two different treatments of scattering; self-consistent Born and multiple sequential scattering are formulated, described, and analyzed for numerical tractability. The relationship between the self-consistent Born and multiple sequential scattering algorithms is described, and the convergence properties of the multiple sequential scattering algorithm are numerically demonstrated by comparing with self-consistent Born calculations. © 1997 American Institute of Physics.
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85.30.De Semiconductor-device characterization, design, and modeling
02.30.-f Function theory, analysis
02.60.-x Numerical approximation and analysis
68.35.Ja Surface and interface dynamics and vibrations

Schottky barrier formation at metal/n-ZnSe interfaces and characterization of Au/n-ZnSe by ballistic electron emission microscopy

R. Coratger, C. Girardin, J. Beauvillain, I. M. Dharmadasa, A. P. Samanthilake, J. E. F. Frost, K. A. Prior, and B. C. Cavenett

J. Appl. Phys. 81, 7870 (1997); http://dx.doi.org/10.1063/1.365395 (6 pages) | Cited 12 times

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Current transport and ballistic electron emission microscopy (BEEM) studies have been carried out on metal contacts fabricated on chemically etched n-ZnSe epitaxial layers grown by molecular beam epitaxy. The contact materials Ag, Sb, Au, Ge/Au, Sn, Ni, and Pd form one or more barrier heights out of the following seven discrete values: 0.90, 1.20, 1.32, 1.50, 1.67, 1.80, and 2.10±0.04 eV observed to date. BEEM work carried out on Au/n-ZnSe systems has identified four levels 1.32 [Morgan et al., J. Appl. Phys. 79, 1532 (1996)], 1.50, 1.67 [Coratger et al., Phys. Rev. B 15, 2357 (1995)] and 1.80 eV to date, confirming Fermi-level pinning at different positions. Schottky barrier formation at metal/n-ZnSe systems cannot be explained by the simple Schottky model. The strong Fermi-level pinning observed could be due to bulk and/or surface defects of the ZnSe material. © 1997 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
73.61.Ga II-VI semiconductors
73.20.At Surface states, band structure, electron density of states
81.05.Dz II-VI semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Photoemission study of the formation of intimate In–InGaAs(100) contacts at room and cryogenic temperatures

D. S. Cammack, S. M. McGregor, J. J. McChesney, I. M. Dharmadasa, S. A. Clark, P. R. Dunstan, S. R. Burgess, S. P. Wilks, and M. Elliott

J. Appl. Phys. 81, 7876 (1997); http://dx.doi.org/10.1063/1.365377 (4 pages) | Cited 1 time

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Previous current–voltage studies of In contacts deposited on atomically clean (intimate) In53Ga47As(100) have indicated the potential to “select” barrier heights in this materials system by cryogenic processing. Soft x-ray photoemission spectroscopy was used to determine the electronic and chemical nature of these interfaces, as a function of formation temperature. Metallization at room temperature results in a predominantly three-dimensional mode of growth, accompanied by the outdiffusion of As. Low temperature metallization appears to reduce clustering and inhibit As outdiffusion. It is proposed that the distribution of surface states and the fermi level pinning position are altered by the changes that occur in the geometry and bonding of the interface at low temperature. © 1997 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
85.40.Ls Metallization, contacts, interconnects; device isolation
79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation

Iteration scheme for the solution of the two-dimensional Schrödinger-Poisson equations in quantum structures

A. Trellakis, A. T. Galick, A. Pacelli, and U. Ravaioli

J. Appl. Phys. 81, 7880 (1997); http://dx.doi.org/10.1063/1.365396 (5 pages) | Cited 89 times

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A fast and robust iterative method for obtaining self-consistent solutions to the coupled system of Schrödinger’s and Poisson’s equations is presented. Using quantum mechanical perturbation theory, a simple expression describing the dependence of the quantum electron density on the electrostatic potential is derived. This expression is then used to implement an iteration scheme, based on a predictor-corrector type approach, for the solution of the coupled system of differential equations. We find that this iteration approach simplifies the software implementation of the nonlinear problem, and provides excellent convergence speed and stability. We demonstrate the approach by presenting an example for the calculation of the two-dimensional bound electron states within the cross section of a GaAs-AlGaAs based quantum wire. For this example, the convergence is six times faster by applying our predictor-corrector approach compared to a corresponding underrelaxation algorithm. © 1997 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
71.10.-w Theories and models of many-electron systems
03.65.Ge Solutions of wave equations: bound states
02.60.Cb Numerical simulation; solution of equations
02.30.Hq Ordinary differential equations

Energy levels in finite barrier triangular and arrowhead-shaped quantum wires

Samita Gangopadhyay and B. R. Nag

J. Appl. Phys. 81, 7885 (1997); http://dx.doi.org/10.1063/1.365361 (5 pages) | Cited 6 times

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Energy eigenvalues and energy shifts are calculated for triangular and arrowhead-shaped GaAs/Ga0.6Al0.4As quantum wires taking into account the finite value of the barrier potential. Calculations were made by using the eigenfunctions of an infinite-barrier right-angled isosceles triangular wire. Calculated values are compared with available experimental results. An equivalence relation is also examined for the estimation of eigenvalues of triangular and arrowhead-shaped quantum wires by knowing the values for rectangular wires. © 1997 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
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