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1 Feb 2001

Volume 89, Issue 3, pp. 1527-1994

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Crystallization of amorphous Cu47Ti34Zr11Ni8

S. C. Glade, J. F. Löffler, S. Bossuyt, W. L. Johnson, and M. K. Miller

J. Appl. Phys. 89, 1573 (2001); http://dx.doi.org/10.1063/1.1332089 (7 pages) | Cited 34 times

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The results of a study on the crystallization of amorphous Cu47Ti34Zr11Ni8 with the use of differential scanning calorimetry, transmission electron microscopy (TEM), x-ray diffraction, field ion microscopy, atom probe tomography (APT), and small-angle neutron scattering (SANS) are presented. These experimental techniques were used to characterize as-prepared samples and specimens heat treated at different temperatures around the glass transition temperature. APT and SANS show that the alloy decomposes into copper-enriched and titanium-enriched regions prior to nucleation and growth of a crystalline phase. TEM shows that the primary nucleating phase has a face centered cubic structure. © 2001 American Institute of Physics.
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61.43.Fs Glasses
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
81.40.Gh Other heat and thermomechanical treatments

Irradiation effect of low energy nitrogen-ion beam during pulsed laser deposition process on the structural and bonding properties of carbon–nitride thin films

J. P. Zhao, Z. Y. Chen, T. Yano, T. Ooie, and M. Yoneda

J. Appl. Phys. 89, 1580 (2001); http://dx.doi.org/10.1063/1.1335643 (8 pages) | Cited 10 times

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Carbon–nitride thin films were deposited by pulsed laser ablation of graphite with assistance of low energy nitrogen-ion-beam irradiation. The nitrogen to carbon (N/C) atomic ratio, bonding state, microstructure, surface morphology, and electrical property of the deposited carbon–nitride films were characterized by x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, micro-Raman spectroscopy, x-ray diffraction (XRD), atomic force microscopy, and four-probe resistance. The irradiation effect of low energy nitrogen-ion beam on the synthesis of carbon–nitride films was investigated. The N/C atomic ratio of the carbon–nitride films reached the maximum at the ion energy of ∼200 eV. The energy of ∼200 eV was proposed to promote the desired sp3-hybridized carbon and the C3N4 phase. Electrical resistivity of the deposited films was also influenced by the low energy nitrogen-ion-beam irradiation. However, the low energy irradiation had little effect on the surface morphology of the films. XRD results revealed the coexistence of the α- and β-C3N4 phases in the deposited thin films. © 2001 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.35.Gy Mechanical properties; surface strains
61.80.Jh Ion radiation effects
62.20.Qp Friction, tribology, and hardness
61.82.Ms Insulators

Manipulation and immobilization of alkane-coated gold nanocrystals using scanning tunneling microscopy

M. Rolandi, K. Scott, E. G. Wilson, and F. C. Meldrum

J. Appl. Phys. 89, 1588 (2001); http://dx.doi.org/10.1063/1.1334919 (8 pages) | Cited 6 times

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Colloidal nanoparticles, comprised of gold nanocrystals, of mean diameter 2.8 nm, coated with an insulating chemically stable self-assembled monolayer of dodecanethiol, have been prepared. Monolayers of nanoparticles have been physisorbed on highly oriented pyrolitic graphite, first by self-assembly, and second by assembly as Langmuir films and subsequent deposition. Nanoparticles have been self-assembled on gold, and immobilized by chemisorption, using decanedithiol during assembly as a linking molecule. Scanning tunneling microscope images of the monolayers are obtained. At high substrate–tip voltages, >0.6 V, the tip is able to climb above the nanoparticles. The tunneling is then a two-step event, tunneling from the substrate to the gold nanocrystal, and subsequently from the gold nanocrystal to the tip. At low voltage, 0.25 V, the Coulomb blockade prevents one extra electron occupying the gold nanocrystal. The tip cannot then climb above the nanoparticles. The theoretical threshold of the blockade is estimated from the nanoparticle size, and shown to be consistent with the observations. At low substrate–tip voltages, rastering of the tip sweeps the nanoparticles from the raster area (but not at high tip voltage). This result has not been described previously, and it is envisaged that it could be used to separate nanoparticles of differing size. However, immobilized isolated nanoparticles are not removed, but only pushed temporarily aside by the scanning tip. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.16.Ta Atom manipulation
68.18.Fg Liquid thin film structure: measurements and simulations
73.23.Hk Coulomb blockade; single-electron tunneling
68.43.Mn Adsorption kinetics

Identification of stable boron clusters in c-Si using tight-binding statics

Weiwei Luo and Paulette Clancy

J. Appl. Phys. 89, 1596 (2001); http://dx.doi.org/10.1063/1.1335644 (9 pages) | Cited 21 times

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As a particularly important p-type dopant, boron exhibits some problematical phenomena during the fabrication of microelectronic devices, especially transient enhanced diffusion (TED) following ion implantation and annealing. TED is due, in large part, to the formation of boron-defect clusters. This article describes a search for particularly stable boron-defect clusters (up to B4I4). A tight-binding method, in conjunction with atomic-scale statics calculations, is used to study boron and boron-defect clusters containing up to four boron atoms and four self-interstitials within a matrix of crystalline silicon. Formation and binding energies are reported for these species. There is a tendency to form a four-atom ring containing two Si self-interstitials and two boron atoms. One guiding principle for the stability of the geometry of the clusters is to maximize the number of unstrained bonds (i.e. with Si-like bond lengths); the higher the extent of unstrained bonds, the lower the formation energy. Symmetry is found to play a smaller role in determining preferred structures. © 2001 American Institute of Physics.
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71.55.Cn Elemental semiconductors
61.72.uf Ge and Si
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Lattice misfit versus performance of thin film electroluminescent structures

E. A. Mastio, W. M. Cranton, and C. B. Thomas

J. Appl. Phys. 89, 1605 (2001); http://dx.doi.org/10.1063/1.1335646 (7 pages) | Cited 1 time

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Thin polycrystalline electroluminescent thin films (TFEL) of ZnS:Mn (phosphor) and Y2O3 (insulator) were deposited individually or as multilayers onto Si (100) substrates. Their crystallinity and the luminescent efficiency of the phosphor films were investigated at varying thermal annealing temperatures. It is shown that the luminescent quality of the phosphor layer increases up to 700 °C, whereas the electroluminescence operating intensity of TFEL devices saturates at 500 °C. The structural analysis of the insulating and phosphor layers shows that they recrystallize at annealing temperatures of, respectively, 500 and 600 °C, and that their lattice misfit doubles at processing temperatures>=500 °C. Since TFEL devices should benefit from enhanced luminescence efficiency and crystallinity at high annealing temperatures, we suggest that the lack of improvement in device performance beyond 500 °C is due to interface alterations. According to previous works, we propose that the lattice misfit increase between the phosphor and dielectric thin films modifies the morphology of the phosphor–insulator boundary inducing a modification of the interface states density, and hence, modifying high field electron transport properties of TFEL devices. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.20.At Surface states, band structure, electron density of states
78.60.Fi Electroluminescence

Role of specimen thickness on the electrical conductivity of single crystalline alumina under electron irradiation

M. M. R. Howlader, C. Kinoshita, K. Shiiyama, and T. Higuchi

J. Appl. Phys. 89, 1612 (2001); http://dx.doi.org/10.1063/1.1336516 (7 pages) | Cited 2 times

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The electrical conductivity of 125-, 332-, and 545-μm-thick single crystalline Kyocera alpha alumina has been measured before, during, and after irradiation with 1 MeV electrons in an applied electric field of 300 kV/m at temperatures up to 723 K. Simultaneous measurements of the bulk and surface conductivity to a total fluence of 8.0×1022 e/m2 (9.4×10−5 dpa and 5.0×109 Gy) at 723 K show no bulk and no surface degradation in the specimen, rather than only a sort of decrease of the conductivity with total dpa. Strong thickness dependence of radiation induced conductivity (RIC) is found and is believed to be due to the effect of electron charge deposition and the production of charged point defects during irradiation. Finally it is suggested that the thickness dependent RIC of the insulating materials must be considered carefully before designing the coating and window materials of fusion reactors. © 2001 American Institute of Physics.
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61.80.Fe Electron and positron radiation effects
61.82.Ms Insulators
72.80.Sk Insulators

Nitrogen doping of tetrahedral amorphous carbon films: Scanning tunneling spectroscopy

Somnath Bhattacharyya, K. Walzer, M. Hietschold, and F. Richter

J. Appl. Phys. 89, 1619 (2001); http://dx.doi.org/10.1063/1.1339854 (6 pages) | Cited 14 times

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Amorphous nitrogenated carbon films with nitrogen atomic concentration between 12% and 29% were deposited using a filtered cathodic vacuum arc and a Kaufman-type ion source. The surface topography of the samples has been investigated by scanning tunneling microscopy in ultrahigh vacuum, showing that the roughness of the film surface decreases with nitrogen concentration. Scanning tunneling spectroscopy is employed to understand the role of nitrogen in the change of the surface microstructure and electronic structure near the Fermi level. The tunneling current (I)–bias voltage (V) curve is flat at low bias regions indicating a finite gap for the sample with low (12%) nitrogen concentration. An increase of tunneling current and its nonlinearity along with the decrease of energy gap occurs in the samples with increase of N concentration. The observed surface density of states [(dI/dV)/(I/V)] has been fitted as a square-root function of bias voltage. An improvement of the quality of these fits in the films with the increase of nitrogen concentration suggests that a depletion of defect density of states near the Fermi level (EF) takes place. These analyses could be attributed to the modification of the structure of amorphous carbon by a large concentration of nitrogen. © 2001 American Institute of Physics.
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71.55.Cn Elemental semiconductors
81.05.U- Carbon/carbon-based materials
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.61.Jc Amorphous semiconductors; glasses
73.61.Cw Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.up Other materials
85.40.Ry Impurity doping, diffusion and ion implantation technology
73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Jv Disordered structures; amorphous and glassy solids

Magnetically driven isentropic compression experiments on the Z accelerator

D. B. Reisman, A. Toor, R. C. Cauble, C. A. Hall, J. R. Asay, M. D. Knudson, and M. D. Furnish

J. Appl. Phys. 89, 1625 (2001); http://dx.doi.org/10.1063/1.1337082 (9 pages) | Cited 55 times

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Isentropic compression experiments (ICE) have been performed on the Z accelerator facility at Sandia National Laboratory. We describe the experimental design that used large magnetic fields to slowly compress samples to pressures in excess of 400 kbar. Velocity wave profile measurements were analyzed to yield isentropic compression equations of state (EOS). The method can also yield material strength properties. We describe magnetohydronamic simulations and results of experiments that used the “square short” configuration to compress copper and discuss ICE EOS experiments that have been performed with this method on tantalum, molybdenum, and beryllium. © 2001 American Institute of Physics.
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64.30.-t Equations of state of specific substances
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
62.50.-p High-pressure effects in solids and liquids

Structural and bonding properties of carbon nitride films synthesized by low energy nitrogen-ion-beam-assisted pulsed laser deposition with different laser fluences

J. P. Zhao, Z. Y. Chen, T. Yano, T. Ooie, M. Yoneda, and J. Sakakibara

J. Appl. Phys. 89, 1634 (2001); http://dx.doi.org/10.1063/1.1334643 (7 pages) | Cited 10 times

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Carbon nitride films were deposited by pulsed Nd:yttrium–aluminum–garnet laser ablation of graphite with assistance of low energy nitrogen-ion-beam bombardment. The nitrogen to carbon (N/C) atomic ratio, surface morphology, bonding state, and microstructure of the deposited carbon nitride films were characterized by x-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, micro-Raman spectroscopy, atomic force microscopy (AFM), and x-ray diffraction. The influence of laser fluence on the synthesis of carbon nitride films was investigated. The N/C atomic ratio of the carbon nitride films can reach the maximum at the highest laser fluence. XPS and FTIR analyses indicated that the bonding state between the carbon and nitrogen in the deposited films was significantly influenced by the laser fluence during deposition. The carbon–nitrogen bonding of C–N and C=N were observed in the films. In addition, α and β C3N4 phases were found to coexist in the carbon nitride films with relative low degree of ordering in the crystal lattice. AFM results indicated that the laser fluence also had a critical effect on the surface structure of the carbon nitride films. © 2001 American Institute of Physics.
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78.66.Nk Insulators
81.15.Fg Pulsed laser ablation deposition
68.35.Np Adhesion
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
78.30.Hv Other nonmetallic inorganics

Differences between interfacial and surface molybdenum in the formation of TiSi2

S.-L. Zhang, Z.-B. Zhang, D.-Z. Zhu, and H.-J. Xu

J. Appl. Phys. 89, 1641 (2001); http://dx.doi.org/10.1063/1.1333736 (6 pages) | Cited 1 time

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Backscattering and diffraction results are presented for the effects of an interfacial or a surface Mo layer on the formation of Ti-silicides during solid-state interaction between Ti films and Si substrates. It is shown that the interfacial and surface Mo are fundamentally different in their involvement in the Ti-silicide formation. The interfacial Mo induces the formation of C40 (Mo,Ti)Si2 at the interface adjacent to the Si substrate already after annealing at 550 °C, in agreement with our previous results. Hence, the desired C54 TiSi2 can grow directly on top of the C40 (Mo,Ti)Si2 at relatively low temperatures as a result of the template effect. The surface Mo is, however, found in a metal-rich silicide presumably (Mo,Ti)5Si3 at 550–600 °C, which eventually converts to (Mo,Ti)Si2 upon annealing at higher temperatures. Underneath this metal-rich silicide lies a fully developed C49 TiSi2 layer. Consequently, the formation of C54 TiSi2 in the presence of surface Mo follows the usual path of the C49–C54 phase transition. This important difference in the participation of Mo in the silicide formation spreads doubts about the validity of using interfacial Mo versus surface Mo to study the dominant mechanism(s) responsible for the enhanced formation of C54 TiSi2. © 2001 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
66.30.Ny Chemical interdiffusion; diffusion barriers
64.70.K- Solid-solid transitions

Structural characteristics of Y2O3 films grown on oxidized Si(111) surface

M.-H. Cho, D.-H. Ko, Y. K. Choi, I. W. Lyo, K. Jeong, T. G. Kim, J. H. Song, and C. N. Whang

J. Appl. Phys. 89, 1647 (2001); http://dx.doi.org/10.1063/1.1337920 (6 pages) | Cited 19 times

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We investigated the characteristics of Y2O3 films grown on an oxidized Si(111) surface, using x-ray diffraction, Rutherford backscattering spectroscopy, and high-resolution transmission electron microscopy. The films grown on the oxidized Si show drastically improved crystallinity, compared with the film grown on clean Si surfaces: channeling minimum yield (Xmin) of 2.5% and full width at half maximum of rocking curve lower than 0.03°. The improvement of the crystallinity was due to the difference of the crystalline structure at the interface between the films grown on the oxidized and clean Si surfaces. Crystalline orientation of Y2O3 islands at the interfacial region was misaligned from the normal substrate direction. The misalignment decreased with increasing the substrate temperature. In particular, the ordering of the oxygen atom in the film grown on oxidized Si was improved compared to that of the Y atom, indicating that the crystallinity of the film is dominantly determined by the arrangement of the oxygen atom in the unit cell. These characteristics of crystalline structure are influenced by the interfacial interactions among SiO2, Y, and Si. The interfacial SiO2 layer can be removed at high growth temperature above 800 °C using the reaction process; the high crystalline Y2O3 film without any interlayer oxide can be obtained. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
68.37.Lp Transmission electron microscopy (TEM)
61.66.Fn Inorganic compounds

Blue photoluminescence in ZnGa2O4 thin-film phosphors

Yong Eui Lee, David P. Norton, Chan Park, and Christopher M. Rouleau

J. Appl. Phys. 89, 1653 (2001); http://dx.doi.org/10.1063/1.1287228 (4 pages) | Cited 22 times

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The growth and properties of luminescent ZnGa2O4 thin films using pulsed laser ablation has been investigated. As-deposited films on glass and (100) MgO substrates exhibit blue-white photoluminescence with a broad emission band under ultraviolet excitation. In situ epitaxial films obtained on single crystal (100) MgO substrates possess enhanced luminescent intensity as compared to polycrystalline films on glass substrates. The enhanced luminescence in epitaxial films presumably reflects lower defect densities due to growth on low energy surfaces. © 2001 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
81.15.Fg Pulsed laser ablation deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Li Other semiconductors

Raman studies on GaAs1−xBix and InAs1−xBix

Prabhat Verma, K. Oe, M. Yamada, H. Harima, M. Herms, and G. Irmer

J. Appl. Phys. 89, 1657 (2001); http://dx.doi.org/10.1063/1.1336561 (7 pages) | Cited 12 times

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The lattice vibrational properties of new semiconductor alloys, GaAs1−xBix and InAs1−xBix, are reported. These alloys, which were grown by metalorganic vapor phase epitaxy technique, contain a small amount (1.2%–3.8%) of Bi. A detail Raman scattering study of these new alloys, which exhibit weak temperature dependence of the band gap with increasing amount of Bi, is reported here. Good crystalline quality and spatial homogeneity was confirmed using micro-Raman technique. The alloys show ternary compound behavior, confirming substitutional incorporation of Bi into the lattice site. New vibrational modes observed were assigned to GaBi-like and InBi-like modes. In addition, phonon-plasmon coupled modes and vibrational modes corresponding to Bi and As materials were also observed. Results are discussed to characterize these new alloys in detail. © 2001 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
63.20.kk Phonon interactions with other quasiparticles
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.20.Nr Semiconductor compounds

Improved electroluminescence of ZnS:Mn thin films by codoping with potassium chloride

K. E. Waldrip, J. S. Lewis, Q. Zhai, M. Puga-Lambers, M. R. Davidson, P. H. Holloway, and S.-S. Sun

J. Appl. Phys. 89, 1664 (2001); http://dx.doi.org/10.1063/1.1338988 (7 pages) | Cited 6 times

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Alternating current thin film electroluminescent devices have been fabricated using sputter-deposited ZnS:Mn with and without codoped potassium chloride via both in situ and ex situ methods. In situ codoping proved to be difficult due to a memory effect in the deposition chamber. Samples codoped with potassium chloride via an ex situ diffusion method exhibited improvements in brightness of up to 70% (572 vs 337 cd/m2) and efficiency of up to 60% (1.95 vs 1.25 lm/W) over noncodoped samples. The threshold voltage increased by ≈5% (160 vs 168 V), and the brightness-versus-voltage curve stabilized more rapidly for the devices. Several possible mechanisms to explain these effects are discussed. While modest microstructural changes contribute to the improvements, changes in point defects which lead to modification of the space charge in the devices appears to be the dominant mechanism. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.60.Pg Display systems
42.79.Kr Display devices, liquid-crystal devices
61.72.J- Point defects and defect clusters

Light scattering from (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 with the tungsten bronze structure: An analogy with relaxor ferroelectrics

I. G. Siny, S. G. Lushnikov, S. I. Siny, V. H. Schmidt, A. A. Savvinov, and R. S. Katiyar

J. Appl. Phys. 89, 1671 (2001); http://dx.doi.org/10.1063/1.1337923 (8 pages) | Cited 7 times

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The Brillouin and Raman scattering from a complex single crystal from the tungsten–bronze family, (K0.5Na0.5)0.2(Sr0.75Ba0.25)0.9Nb2O6 doped with Cu2+ (KNSBN:Cu), have been comparatively studied in a wide temperature range around the ferroelectric transition. Step-like anomalies in hypersonic velocity and damping confirm the first-order structural transition. These anomalies look like some perturbations on the high-temperature slopes of both a broad dip in sound velocity and a broad maximum in damping that develop in a wide temperature range. The acoustic behavior of KNSBN:Cu does not simply follow the Landau theory prediction valid for many ferroelectrics. Instead it resembles that of relaxors, to which the KNSBN:Cu behavior is analogous intrinsically. The total intensity of the Raman spectra as well as the intensity of separate internal and external vibrations and their width correlate with acoustic anomalies, namely there are step-like drops at the same temperature as the first-order transition and a broad range where the intensity is drastically increased. All these broad anomalies imply the existence of a wide preceding phase in respect to the relaxor ferroelectric state. Unusual properties of this preceding phase are discussed as well as the phase diagram relation to the dynamical evolution of other relaxors from the perovskite family, such as PbMg1/3Nb2/3O3 and Na1/2Ba1/2TiO3. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.35.+c Brillouin and Rayleigh scattering; other light scattering
77.80.B- Phase transitions and Curie point
78.30.Hv Other nonmetallic inorganics

Luminescence properties of nanocrystalline Y2O3:Eu3+ in different host materials

R. Schmechel, M. Kennedy, H. von Seggern, H. Winkler, M. Kolbe, R. A. Fischer, Li Xaomao, A. Benker, M. Winterer, and H. Hahn

J. Appl. Phys. 89, 1679 (2001); http://dx.doi.org/10.1063/1.1333033 (8 pages) | Cited 99 times

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In this study, the optical properties of nanocrystalline europium doped yttria, Y2O3:Eu3+ were investigated in dependence on different caging hosts such as porous MCM-41, porous silica, and porous alumina with pore sizes ranging between 2.7 to 80 nm. These results were compared to nanopowders measured in air and aqueous solution whose particle sizes were 5 nm and 8 nm, respectively. All these results were compared to a commercial lamp phosphor powder with a grain size of about 5 μm. The structural properties of the samples were determined by x-ray diffraction and transmission electron microscopy. Investigated optical properties are the photoluminescence emission spectra, the excitation spectra, the lifetimes, and the quantum efficiencies. A heavy dependence of the charge transfer process on the surrounding will be reported and discussed. © 2001 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
73.22.-f Electronic structure of nanoscale materials and related systems

Optical absorption of Zn1−xMnxGa2Se4 diluted magnetic semiconductors: Variation of the energy gap with composition and temperature

A. Millán and M. C. Morón

J. Appl. Phys. 89, 1687 (2001); http://dx.doi.org/10.1063/1.1337601 (5 pages) | Cited 4 times

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Optical absorption and magnetic susceptibility data of the Zn1−xMnxGa2Se4 family of compounds have been collected in the temperature range 10–300 K. One of the most interesting aspects of this series is the availability of samples in the whole composition range, in contrast with most diluted magnetic semiconductors that are only miscible in a limited range of compositions. Temperature-independent absorption bands with maxima at 2.33, 2.49, and 2.66 eV have been found that are assigned to electron transitions from the 6A1 ground state to the 4T1, 4T2, and 4A1, or 4E excited states of the Mn++ ion in a tetrahedral crystalline field. The optical spectra exhibit a temperature dependent absorption edge in the 350–600 nm region that corresponds to a direct band gap. The band gap energy has been determined as a function of atomic concentration and temperature. At room temperature, the variation of the energy gap Eg with the Mn content shows a rather anomalous behavior that consists of an initial decrease for x<0.1, followed by a roughly flat variation for 0.1<x<0.5, and a nearly linear increase for x>0.5. An analogous evolution of Eg with x is found when decreasing temperature. Such behavior has been compared with that reported for analogous systems. The variation of Eg with temperature follows Varshni’s relation for all compositions. A monotonic increase of the magnetic susceptibility with x is found within the whole range of Mn content. © 2001 American Institute of Physics.  
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78.40.Fy Semiconductors
75.50.Pp Magnetic semiconductors
75.30.Cr Saturation moments and magnetic susceptibilities
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.70.Ch Crystal and ligand fields

Photoluminescence studies of GaN layers grown by hydride vapor phase epitaxy

P. W. Yu, C. S. Park, and S. T. Kim

J. Appl. Phys. 89, 1692 (2001); http://dx.doi.org/10.1063/1.1337589 (4 pages) | Cited 19 times

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Photoluminescence of gallium nitride (GaN) layers 7.5–870 μm thick was studied with changes in temperature and excitation intensity. These layers were grown by hydride vapor phase epitaxy on a buffer layer of aluminum nitride (AlN). The photoluminescence emission consists of the shallow-donor bound exciton at 3.471 eV and the free hole-to-electron bound to a donor (possibly a nitrogen vacancy VN or oxygen) transition at 3.40–3.433 eV. The peak position varies depending on the thickness of the GaN and AlN layers. The localized donor due to donor concentration fluctuation is attributed to the variable peak position. The observed 3.269 eV emission is attributed to a donor–acceptor pair transition. The relationship between the peak and the excitation intensity is described accurately by a theoretical description which yields Ed=32 meV and Ea=230 meV, which originate, respectively, from a silicon donor and carbon acceptor. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
61.72.J- Point defects and defect clusters

Photoluminescence properties of δ-doped barrier layers in modulation-doped InAlAs/InGaAs field-effect transistor structures

Kazuo Watanabe and Haruki Yokoyama

J. Appl. Phys. 89, 1696 (2001); http://dx.doi.org/10.1063/1.1338523 (8 pages) | Cited 2 times

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A photoluminescence peak from the Si δ-doped InAlAs barrier layers (δ peak) is found around the InAlAs exciton peak from the buffer layer in 15 modulation-doped InAlAs/InGaAs heterostructure field-effect transistor (HFET) structure wafers. The δ peak position ordinarily shifts to shorter wavelength with increasing δ doping concentration. The intensity reduction of the δ peak due to raising the temperature from 6 K is considerably slower than that of the InAlAs exciton peak. The excitation spectrum of the δ peak is clearly different from that of the InAlAs exciton peak and seems to reflect the optical absorption dominated by the potential slope in the upper side of the barrier layer and the quasi-Fermi level. The δ peak is not detected from HFET structures without the contact layers. The δ peak is attributed to the recombination of electrons from the δ-doped layer and photogenerated holes weakly confined in the upper side of the barrier layer. © 2001 American Institute of Physics.
Show PACS
85.30.Tv Field effect devices
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
85.30.De Semiconductor-device characterization, design, and modeling
71.35.-y Excitons and related phenomena
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