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1 Aug 1999

Volume 86, Issue 3, pp. 1177-1776

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Evolution process of cross-hatch patterns and reduction of surface roughness in (InAs)m(GaAs)n strained short-period superlattices and InGaAs alloy layers grown on GaAs

K. Samonji, H. Yonezu, Y. Takagi, and N. Ohshima

J. Appl. Phys. 86, 1331 (1999); http://dx.doi.org/10.1063/1.370891 (9 pages) | Cited 10 times

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We investigated the formation process of cross-hatch patterns (CHPs) and the lattice relaxation process in the growth of an (InAs)1(GaAs)4 strained short-period superlattice (SSPS) and an In0.2Ga0.8As alloy layer on GaAs(100) substrates. By using x-ray diffraction and cross-sectional transmission electron microscopy, it was found that the lattice relaxation in the (InAs)1(GaAs)4SSPS proceeded as fast as that in the In0.2Ga0.8As alloy layer. The surfaces of the grown layers showed CHPs, and the surface roughness increased by means of the evolution of the CHPs. The surface roughness of the SSPSs was larger than that of the alloy layers, whereas no apparent difference was observed in the lattice relaxation process between the SSPSs and the alloy layers. Additionally, the height of surface ridges parallel to the [0math1] direction was higher than that parallel to the [011] direction. We observed the distribution of highly strained InAs and GaAs islands on the surfaces of strained InGaAs layers by using an atomic force microscope. As a result, it was clarified that the InAs islands were accumulated on top of the surface ridges, whereas the GaAs islands were distributed uniformly on the surface of strained InGaAs layer. It was considered that the nonuniform incorporation of In atoms during growth of layers contributes mainly to the evolution of CHPs in the InGaAs-on-GaAs heteroepitaxy. We propose a developmental model of CHPs based on the surface diffusion of the In atoms. In this model, the asymmetry of CHPs was well understood by anisotropy in surface diffusion length of In atoms. Additionally, it was clarified that the evolution of CHPs in the growth of InGaAs at a high temperature can be suppressed by growing a fully relaxed InGaAs layer at a low temperature before the high-temperature growth. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation

Effects of composition on the formation temperatures and electrical resistivities of C54 titanium germanosilicide in Ti–Si1−xGex systems

J. B. Lai and L. J. Chen

J. Appl. Phys. 86, 1340 (1999); http://dx.doi.org/10.1063/1.370892 (6 pages) | Cited 5 times

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The effects of alloy composition on the formation temperature and electrical resistivities of C54 titanium germanosilicide formed during the Ti/Si1−xGex (x = 0, 0.3, 0.4, 0.7, 1) solid state reaction have been investigated. Ti5(Si1−yGey)3, C49– and C54–Ti(Si1−zGez)2 were observed to form in the Ti/Si1−xGex (x ≥ 0.4) systems. On the other hand, Ti6(Si1−yGey)5 and C54–Ti(Si1−zGez)2 were found in the Ti/Si1−xGex (x≧0.7) systems. For both cases, the relationship of x>y>z was found. The appearance and agglomeration temperature of low-resistivity C54–Ti(Si1−zGez)2 were both found to decrease with the Ge concentration. The resistivities of C54–Ti(Si1−zGez)2 were measured to be 15–20 μΩ/cm. The segregation of Si1−wGew (w>x) was found in all samples annealed above 800 °C. The effects of thermodynamic driving force, kinetic factor, and composition of the micro-area are discussed. © 1999 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
61.72.Cc Kinetics of defect formation and annealing
73.40.Ns Metal-nonmetal contacts
64.75.-g Phase equilibria
73.61.At Metal and metallic alloys
85.40.Ls Metallization, contacts, interconnects; device isolation

Microstructure and interfacial states of silicon dioxide film grown by low temperature remote plasma enhanced chemical vapor deposition

Young-Bae Park and Shi-Woo Rhee

J. Appl. Phys. 86, 1346 (1999); http://dx.doi.org/10.1063/1.370893 (9 pages) | Cited 7 times

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The properties of SiO2 film and the Si/SiO2 interface formed by remote plasma enhanced chemical vapor deposition with the addition of chlorine into SiH4–N2O have been investigated. With the chlorine addition, the deposition rate increased at low deposition temperatures but at temperatures above 150 °C, it decreased because of the desorption of surface halide species. Chlorine at the Si/SiO2 interface prevented further subcutaneous oxidation and formed strong, terminal site Si–Cl bonds which reduced the interface state density. The substitution reaction of O and H with Cl in the bulk oxide film leads to a disordered film structure and decreased hydrogen concentration. The surface roughness increased and the refractive index decreased with increased Cl2 addition. With chlorine addition of less than 6 vol %, the interface trap density (located at ∼ Ev+0.3–0.4 eV) significantly decreased down to the 1–3×1011 eV cm2 level at the Si midgap. At high chlorine partial pressure and temperature, the local interface trap density (located at ∼ Ev+0.7–0.8 eV) increased due to increased structural disorder resulting from breakage of the Si–O bond. © 1999 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
73.20.At Surface states, band structure, electron density of states
78.66.Nk Insulators
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.Db Elemental semiconductors and insulators

Growth of epitaxial CoSi2 on SiGe(001)

B. I. Boyanov, P. T. Goeller, D. E. Sayers, and R. J. Nemanich

J. Appl. Phys. 86, 1355 (1999); http://dx.doi.org/10.1063/1.370894 (8 pages) | Cited 11 times

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A technique for achieving epitaxial growth of (001)-oriented CoSi2 on strained epitaxial layers of Si1−xGex(001) is described. The technique is based on a variation of the template method, and is designed to control the local environment of Co atoms at the CoSi2/SiGe interface. The effects of the Co–Ge interactions on the interfacial reaction and the epitaxial orientation and the morphology of the silicide film were investigated. This reaction was found to cause pitting in (001)-oriented CoSi2 films, and to stabilize the (22math) orientation for films codeposited under conditions where CoSi2(001) growth is achieved on Si(001) substrates. The (22math)-oriented CoSi2 films were islanded after annealing at 700 °C. The islands were terminated by (math11) and (110) facets inclined at 15.8° and 19.5°, respectively, from CoSi2 [22math] towards CoSi2 [114]. These results were interpreted in terms of reduction of interfacial and surface energies, and geometric effects. Silicide films up to 730-Å-thick were deposited and annealed up to 900 °C. The films were stable against agglomeration, and retained tensile stress in the CoSi2 layer after annealing at 700 °C. The rms roughness of the CoSi2 films was comparable to that of the Si(001) substrate—less than 15 Å over areas as large as 20×20 μm2. Films annealed at 900°C were severely agglomerated. © 1999 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Md Surface thermodynamics, surface energies
68.60.Dv Thermal stability; thermal effects

Effect of I− impurity on the efficiency of silver cluster formation on AgBr microcrystal surfaces

R. K. Hailstone

J. Appl. Phys. 86, 1363 (1999); http://dx.doi.org/10.1063/1.370895 (7 pages) | Cited 2 times

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Computer simulation is used to study the effect of iodide impurity on silver cluster formation on AgBr microcrystals. The simulation is based on a nucleation-and-growth model of silver cluster formation in competition with recombination of electrons and holes. The efficiency of silver cluster formation is calculated as a function of microcrystal size and shown to increase with size for the impurity-free control, contrary to experimental data. This behavior is due to a partitioning of the hole between free and trapped states which favors the free side as size increases. As a result, recombination decreases and efficiency increases at large microcrystal size. Iodide impurity decreases efficiency relatively more at larger sizes because it introduces an internal recombination pathway not present in the control simulation. Because of their larger volume-to-surface-area ratios, the larger microcrystals are affected more by this additional recombination pathway than smaller microcrystals. © 1999 American Institute of Physics.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
07.68.+m Photography, photographic instruments; xerography
42.70.Gi Light-sensitive materials
73.25.+i Surface conductivity and carrier phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
68.35.Dv Composition, segregation; defects and impurities

Evolution of phase composition and associated properties in the process of growth of thin films

S. A. Kukushkin and A. V . Osipov

J. Appl. Phys. 86, 1370 (1999); http://dx.doi.org/10.1063/1.370896 (7 pages)

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A complete set of equations describing the evolution of phase composition of an island ensemble at the stage of the Ostwald ripening in the process of thin-film growth is derived and its solution is found. The size distribution function of islands in solid solutions is obtained for different types of growth mechanisms. The general approach to control phase composition and associated properties (electric, optical, mechanical, and others) in formed multicomponent systems is elaborated. It is shown that the most favorable conditions to control these properties occur at the Ostwald ripening stage and also during nonlinear phenomena, such as self-excited oscillations or self-organization. The relationship between size and composition of the new phase nuclei formed in the course of condensation of solid solution films is revealed. A set of equations describing the evolution of the size distribution function of the properties in island films of solid solutions during changes in external parameters of the system is derived and solved. We show that substantial dependence of composition on external parameters is revealed for the sizes of islands with radius R ⩽ 10−8 m, irrespective of the type of substance. For island-type films of stoichiometric composition, the diagram for coexistence of appropriate properties is plotted in the concentration-temperature coordinates that allows to us determine the conditions required to obtain the properties. Probable periodic changes in time and space of various properties on multicomponent systems undergoing the first order phase transition are predicted. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification

Green photoluminescence band in γ-irradiated oxygen-surplus silica glass

Yuryo Sakurai and Kaya Nagasawa

J. Appl. Phys. 86, 1377 (1999); http://dx.doi.org/10.1063/1.370897 (5 pages) | Cited 14 times

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Previous studies have reported the existence of a green photoluminescence (PL) band in oxygen-deficient silica glass when exposed to ultraviolet (UV) light. Oxygen deficient defects (Eδ′) were thought to be the origin of this PL band. In this article, we describe the characteristics of a green PL band in oxygen-surplus silica glass (excited by visible and UV light). At room temperature, we observed the full width at half maximum and lifetime of this PL band to be about 0.2 eV and 300 ns, which differed from the previously reported values of 0.4 eV and 20–30 ns, respectively. We propose that the peroxy radical (O3 ≡ Si–O–O↑,↑: unpaired electron) or other oxygen surplus defects are the cause of this green PL band rather than oxygen deficient defects. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
61.43.Fs Glasses
61.80.Ed γ-ray effects
61.82.Ms Insulators

Optical constants of amorphous Se

Takeshi Innami, Takayuki Miyazaki, and Sadao Adachi

J. Appl. Phys. 86, 1382 (1999); http://dx.doi.org/10.1063/1.370898 (6 pages) | Cited 9 times

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The pseudodielectric-function spectra, ϵ(E) = ϵ1(E)+iϵ2(E), of amorphous (a-) selenium (Se) in the 1.2–5.2 eV photon-energy range at room temperature were measured by spectroscopic ellipsometry. The a-Se films investigated were deposited by vacuum evaporation in a base pressure of 2×10−6 Torr on Si(100) substrates at room temperature. The ϵ2(E) spectrum showed only a broad peak at ∼4 eV. Such a structureless feature is known to be typically observed in amorphous semiconductors. An ex situ atomic-force-microscopy image confirmed a microscopically flat surface (root-mean-square roughness of ∼0.4 nm) with relatively sharp cones in spots. The Bruggeman effective-medium-approximation analysis suggested that the correction for this microroughness is very small (Δϵ1,2<0.2). The present ϵ(E) data and previously published data were used for the modeling of the optical constants of a-Se over the 0–15 eV photon-energy range. Dielectric-related optical constants, such as the complex refractive index, absorption coefficient, and normal-incidence reflectivity, of a-Se were also presented. © 1999 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.66.Jg Amorphous semiconductors; glasses
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.35.B- Structure of clean surfaces (and surface reconstruction)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Optical limiting and thermal lensing studies in C60

S. S. Harilal, C. V. Bindhu, V. P. N. Nampoori, and C. P. G. Vallabhan

J. Appl. Phys. 86, 1388 (1999); http://dx.doi.org/10.1063/1.370899 (5 pages) | Cited 25 times

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Optical limiting and thermo-optic properties of C60 in toluene are studied using 532 nm, 9 ns pulses from a frequency-doubled Nd:YAG laser. Optical limiting studies in these fullerene molecules lead to the conclusion that reverse saturable absorption is the major mechanism for limiting properties in these molecules. Thermal lensing measurements are also performed in fullerene solutions. The quadratic dependence of thermal lens signal on incident energy confirms that enhanced optical absorption by the sample via excited triplet state absorption may play a leading role in the limiting property. © 1999 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Interactions of intentionally diffused hydrogen with nitrogen acceptors and nitrogen related donor centers in molecular beam epitaxy grown ZnSe

H. Pelletier, B. Theys, A. Lusson, E. Tournié, J. Chevallier, Y. Marfaing, and J. P. Faurie

J. Appl. Phys. 86, 1393 (1999); http://dx.doi.org/10.1063/1.370900 (5 pages) | Cited 2 times

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Nitrogen doped ZnSe layers grown by molecular beam epitaxy have been exposed to a hydrogen or deuterium plasma. Deuterium diffusion profiles have been measured by secondary ion mass spectroscopy. The main feature of these profiles is the presence of a plateau on which the H concentration closely matches the total N content of the layers. Electrical and photoluminescence studies of the layers, before and after hydrogen plasma exposure, show that both acceptor and donor N-related centers are passivated by hydrogen. These results demonstrate that in ZnSe:N hydrogen passivates the nitrogen acceptors and the related nitrogen donors. © 1999 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Dz II-VI semiconductors
61.72.S- Impurities in crystals
66.30.J- Diffusion of impurities
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors

Raman characterization of germanium nanocrystals in amorphous silicon oxide films synthesized by rapid thermal annealing

W. K. Choi, V. Ng, S. P. Ng, H. H. Thio, Z. X. Shen, and W. S. Li

J. Appl. Phys. 86, 1398 (1999); http://dx.doi.org/10.1063/1.370901 (6 pages) | Cited 49 times

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Raman characterization of germanium (Ge) nanocrystals embedded in amorphous silicon oxide (a-SiO2) films synthesized by rapid thermal annealing (RTA) has been carried out. The samples were prepared by cosputtering Ge and SiO2 targets using a rf magnetron sputtering machine. Ge nanocrystals can only be obtained from samples sputtered with six pieces of Ge attached to the SiO2 target. For samples annealed at different RTA temperatures, the Raman spectra indicated a transition from amorphous to nanocrystalline Ge when annealed between 600 and 750 °C. The spectra were analyzed in terms of phonon confinement model and the estimated nanocrystal size was between 20 and 66 Å. A minimum annealing time of 160 s at 750 °C was necessary for Ge nanocrystal formation. Strong visible broadband photoluminescence was observed from the nanocrystals and the photoluminescence showed a blueshift with decrease in the nanocrystal size. The effect of compressive stress on nanocrystal growth was examined by varying the rampup and rampdown rates of the RTA process. The compressive stress was shown to affect the growth of the nanocrystals. © 1999 American Institute of Physics.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Jg Amorphous semiconductors; glasses
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Cy Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.40.Gh Other heat and thermomechanical treatments
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.50.-x Vibrational states in disordered systems

Infrared 45° reflectometry of very thin films

A. Silva-Castillo and F. Pérez-Rodríguez

J. Appl. Phys. 86, 1404 (1999); http://dx.doi.org/10.1063/1.370902 (6 pages) | Cited 4 times

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It is shown that the spectra given by the difference between the reflectivity for p-polarized light and the squared reflectivity for s-polarized light (Rp−Rs2) with an angle of incidence of 45° can be used for directly determining the frequencies of zone-center transverse optical (ωTO) and longitudinal optical (ωLO) phonons in very thin polar-semiconductor films on substrates. These spectra are also useful for measuring resonance frequencies of both transverse and longitudinal optical confined phonons in ultrathin layers of superlattices. © 1999 American Institute of Physics.
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78.66.Hf II-VI semiconductors
07.60.Hv Refractometers and reflectometers
78.30.Fs III-V and II-VI semiconductors
63.20.-e Phonons in crystal lattices
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.66.Fd III-V semiconductors

Defect clusters and thermoluminescence in LiF crystals

A. T. Davidson, A. G. Kozakiewicz, D. J. Wilkinson, and J. D. Comins

J. Appl. Phys. 86, 1410 (1999); http://dx.doi.org/10.1063/1.370903 (5 pages) | Cited 15 times

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The thermoluminescence of pure and doped LiF crystals has been measured following irradiation at ambient temperature with gamma and x rays. Factors investigated include the effects of dopants (Mg, Mg/Ti, and Fe) and of dose. Results are compared with optical absorption and photoluminescence measurements made previously on the same crystals. The role of F, F3+, Z2, and colloids in the emission process is discussed. Some new effects are reported including step-like features in the glow curves at large doses. These are explained in terms of the clustering of interstitial defects formed during radiolysis. © 1999 American Institute of Physics.
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78.60.Kn Thermoluminescence
61.80.Ed γ-ray effects
61.80.Cb X-ray effects
61.72.J- Point defects and defect clusters

Visible photoluminescence in hydrogenated amorphous silicon grown in microwave plasma from SiH4 strongly diluted with He

J. Dian, J. Valenta, J. Hála, A. Poruba, P. Horváth, K. Luterová, I. Gregora, and I. Pelant

J. Appl. Phys. 86, 1415 (1999); http://dx.doi.org/10.1063/1.370904 (5 pages) | Cited 2 times

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Room temperature visible photoluminescence (PL) of wide-band gap hydrogenated amorphous silicon (a-Si:H) thin films prepared in SiH4 microwave plasma strongly diluted with He is reported. Films were characterized by means of optical and infrared absorption, hydrogen thermal desorption, and Raman scattering. The band gap of a-Si:H films varies within the interval 2.0–2.2 eV, corresponding PL maxima are located at 1.4–1.6 eV. The highest PL intensity was observed in samples with a position of H–Si–H symmetric stretching vibration of the –(SiH2)n– units near the frequency of 2100 cm−1. The strong evidence for two distinct types of PL processes is presented: one being linked with oligosilanes and the second one attributed to electron-hole recombination in tail states. © 1999 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.55.Ap Elemental semiconductors
81.05.Gc Amorphous semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
78.35.+c Brillouin and Rayleigh scattering; other light scattering
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
63.50.-x Vibrational states in disordered systems
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
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Pseudopotential methods for superlattices: Applications to mid-infrared semiconductor lasers

Gregory C. Dente and Michael L. Tilton

J. Appl. Phys. 86, 1420 (1999); http://dx.doi.org/10.1063/1.370905 (10 pages) | Cited 48 times

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Many mid-infrared semiconductor laser sources are now being developed with superlattice active regions. Calculations of gain, index of refraction, and intervalence subband absorption for these laser materials require accurate subband energies, wave functions, and radiative matrix elements. We have recently begun using a solution method based on the empirical pseudopotential method (EPM). This method shows particular strength in analyzing structures with short periods or thin layers, for which the standard method, based on k⋅p perturbation theory and the envelope function approximation, may be problematical. We will describe the EPM applied to bulk solids and then demonstrate our direct generalization of the method for applications to superlattice structures. Calculations for recently developed mid-infrared semiconductor lasers using type-II superlattice active regions will be used to illustrate the method. © 1999 American Institute of Physics.
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71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Electronic structure of the layered compound Ti3GeC2

Yanchun Zhou and Zhimei Sun

J. Appl. Phys. 86, 1430 (1999); http://dx.doi.org/10.1063/1.370906 (3 pages) | Cited 7 times

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The electronic structure and properties of layered ceramic Ti3GeC2 have been examined by means of ab initio linear combination of atomic orbital calculations. The calculated band structure shows Ti3GeC2 to be strongly metallic with high densities of states at the Fermi level. The electrical conductivity is dominated by a Ti (2) 3d state with less contribution from Ti (1) 3d, Ge 4p, and C 2p states. The major factors governing the electronic properties are pd hybridization from Ti 3d, Ge 4p, and C 2p states, and p-d bonding stabilizes the structure. © 1999 American Institute of Physics.
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71.20.Gj Other metals and alloys

Deep hole traps in Be-doped Al0.5Ga0.5As layers grown by molecular beam epitaxy

J. Szatkowski, E. Płaczek-Popko, K. Sierański, and O. P. Hansen

J. Appl. Phys. 86, 1433 (1999); http://dx.doi.org/10.1063/1.370907 (6 pages) | Cited 2 times

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Deep hole traps in p-type Al0.5Ga0.5As grown by molecular beam epitaxy have been studied by the deep-level transient-spectroscopy method applied to samples with a Schottky diode configuration. Five hole traps, labeled as H0 to H4, were found. For traps H1, H3, and H4 the activation energies for emission were ET1 = 0.14 eV, ET3 = 0.40 eV, and ET4 = 0.46 eV, respectively. Hole emission from trap H2 was dependent on the external electric field. The emission rate obeyed the Poole–Frenkel relation. When extrapolated to zero electric field, the thermal activation energy for hole emission was ET2,0 = 0.37 eV. Capture cross sections for traps H1 and H4 were thermally activated with energy barriers EB1 = 0.04 eV and EB4 = 0.18 eV, respectively. © 1999 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Compensation introduced by defect complexes in p-type ZnSe

Tian-Ling Ren, Jia-Lin Zhu, Ziqiang Zhu, and Takafumi Yao

J. Appl. Phys. 86, 1439 (1999); http://dx.doi.org/10.1063/1.370908 (4 pages)

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Defect complexes in N-doped and As-doped ZnSe are studied by using the discrete-variational local-density-functional method within a cluster model. Based on the difference of formation energy between two complexes, it is found that the NSe–Zn–VSe complex is a more efficient acceptor compensator than the NSe–Znint complex in N-doped ZnSe, while the AsSe–Znint complex is a more efficient acceptor compensator than the AsSe–Zn–VSe complex in the As-doped ZnSe. The NSe–Zn–NSe complex with a 170 meV acceptor level and the NSe–NZn complex with an 88 meV donor level are respectively identified. The existence of donor states of N molecules in ZnSe is confirmed. © 1999 American Institute of Physics.
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71.55.Gs II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Modeling and characterization of a strained Si/Si1−xGex transistor with δ-doped layers

Linda S. Geux and Ken Yamaguchi

J. Appl. Phys. 86, 1443 (1999); http://dx.doi.org/10.1063/1.370909 (6 pages) | Cited 2 times

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A two-dimensional model of a strained Si/Si1−xGex transistor with δ-doped layers was developed. A semiclassical drift diffusion model is used to study the effects of different conduction-band offsets and variation of the distance between the Si channel and an n-type δ-doped layer as well as the thickness of this δ-doped layer at room temperature. We found that a large conduction-band offset, or a large Ge concentration, confines electrons more strongly to the Si channel. These factors raise the drain current when the doping level per unit area is constant. The area between the Si channel and the δ-doped layer and the δ-doped layer itself forms a barrier to electrons donated by the donor atoms in the δ-doped layer. Hence, the smaller the distance between the Si channel and the δ-doped layer and the thinner the δ-doped layer, the larger the number of electrons in the Si channel. Through the present analysis, an optimum design concept is clarified for device applications of Si/Si1−xGex systems. © 1999 American Institute of Physics.
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85.30.De Semiconductor-device characterization, design, and modeling
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states

Scanning tunneling spectroscopy study of erbium doped GaSb crystals

P. Hidalgo, B. Méndez, J. Piqueras, J. Plaza, and E. Diéguez

J. Appl. Phys. 86, 1449 (1999); http://dx.doi.org/10.1063/1.370910 (3 pages) | Cited 3 times

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Er doped GaSb single crystals have been studied by scanning tunneling spectroscopy (STS) and cathodoluminescence (CL) in a combined scanning electron microscope–scanning tunnelling microscope system. The surface band gap in doped samples has been found to be about 0.5 eV while in undoped crystals the gap is close to the bulk value. Inhomogeneities in the local electronic properties of the doped crystals are studied by a correlation of the CL images and STS data. © 1999 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
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

Effects on the resonant tunneling characteristics of a double-barrier diode of intentional and unintentional dopings in the quantum well

J. W. Sakai, P. H. Beton, L. Eaves, P. C. Main, and M. Henini

J. Appl. Phys. 86, 1452 (1999); http://dx.doi.org/10.1063/1.370911 (4 pages) | Cited 4 times

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Donor-assisted resonant tunneling in nominally symmetric GaAs/(AlGa)As large area double-barrier diodes is investigated. The log(I)–V characteristics are used to evaluate doping density in the quantum well and are investigated in connection with donor cluster-assisted resonant tunneling. The single-donor-related feature in the resonant-tunneling characteristics is used to detect the presence of donors in the quantum well, even at concentrations of the order of the lowest achieved so far in molecular beam epitaxy GaAs. Expected effects of the presence of donors in the quantum well on the log(I) vs V characteristics are discussed. © 1999 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Kk Junction diodes
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.40.Ry Impurity doping, diffusion and ion implantation technology

A comparison of photoluminescence properties of InGaAs/GaAs quantum dots with a single quantum well

Mei-Ying Kong, Xiao-Liang Wang, Dong Pan, Yi-Ping Zeng, J. Wang, and Weikun Ge

J. Appl. Phys. 86, 1456 (1999); http://dx.doi.org/10.1063/1.370912 (4 pages) | Cited 11 times

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Variable temperature photoluminescence (PL) measurements for In0.3Ga0.7As(6 nm)/GaAs(34 nm) quantum dot superlattices with a period of 20 and an In0.3Ga0.7As(6 nm)/GaAs(34 nm) reference single quantum well have been conducted. It is found that the temperature dependence is different between the quantum dots and the reference single quantum well. The PL peak energy of the single quantum well decreases faster than that of the quantum dots with increasing temperature. The PL peak energy for the InGaAs/GaAs quantum dots closely follows the InAs band gap in the temperature range from 11 to 170 K, while the PL peak energy for the InGaAs/GaAs quantum well closely follows the GaAs band gap. In comparison with InAs/GaAs quantum dots, the InGaAs/GaAs quantum dots are more typical as a zero-dimensional system since the unusual PL results, which appear in the former, are not obvious for the latter. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Above-barrier states in GaAs–AlGaAs superlattices studied by photoconductivity and photoreflectance

J. C. Fan, Y. F. Chen, D. Y. Lin, Y. S. Huang, M. C. Chen, and H. H. Lin

J. Appl. Phys. 86, 1460 (1999); http://dx.doi.org/10.1063/1.370965 (3 pages) | Cited 6 times

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We report that the quasibound states at the above-barrier region in AlGaAs–GaAs superlattices can be clearly observed at room temperature by photoconductivity as well as photoreflectance measurements. We provide concrete evidence to confirm that free-carrier confinement at barrier layer does exist. It is also found that the barrier-width dependence of the above-barrier transition energies can be described quite well by the modified Messiah’s calculation. However, the simple calculation using the constructive interference condition can only explain the transitions at lower energies, and fails with increasing transition energy. © 1999 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
78.66.Fd III-V semiconductors
73.50.Pz Photoconduction and photovoltaic effects
78.20.-e Optical properties of bulk materials and thin films

n-Si/i-p-i SiGe/n-Si structure for SiGe microwave power heterojunction bipolar transistor grown by ultra-high-vacuum chemical molecular epitaxy

Jinshu Zhang, Xiaojun Jin, Hongyong Jia, Peiyi Chen, Pei-Hsin Tsien, M. X. Feng, Q. Y. Lin, and Tai-Chin Lo

J. Appl. Phys. 86, 1463 (1999); http://dx.doi.org/10.1063/1.370913 (4 pages)

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The n-Si/i-p-i SiGe/n-Si structure, grown by ultra-high-vacuum chemical molecular epitaxy, was analyzed by cross-sectional transmission electron microscopy and secondary ion mass spectroscopy. It is shown that no defects are observed in the n-Si/i-p-i SiGe/n-Si structure, the interfaces between the SiGe layer and the n-Si layers are clear and planar, both the Ge and boron atoms are uniformly distributed in the p-SiGe, and the profiles of boron and Ge are abrupt from the n-Si to the SiGe layer. A high-performance microwave power SiGe heterojunction bipolar transistor was fabricated using the n-Si/i-p-i SiGe/n-Si structure. Therefore, ultra-high-vacuum chemical molecular epitaxy is one of the most promising methods for the growth of the Si/SiGe strained epilayers. © 1999 American Institute of Physics.
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85.30.Pq Bipolar transistors
84.30.Jc Power electronics; power supply circuits
81.15.Kk Vapor phase epitaxy; growth from vapor phase
84.40.-x Radiowave and microwave (including millimeter wave) technology
81.05.Hd Other semiconductors
85.40.Sz Deposition technology
81.05.Cy Elemental semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Properties of the second-order nonlinear optical susceptibility χ(2) in asymmetric undoped AlGaAs/InGaAs double quantum wells

Tae-ik Park, Godfrey Gumbs, and Y. C. Chen

J. Appl. Phys. 86, 1467 (1999); http://dx.doi.org/10.1063/1.370914 (5 pages) | Cited 6 times

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The second-order nonlinear optical susceptibility χ(2) for second-harmonic generation is calculated for the 11H transition of a graded double quantum well (DQW) structure of undoped GaAs/AlxGa1−xAs. These results are compared with the single quantum well (QW). Our results show that the values of χ(2) have optimal magnitudes dependent on the width, depth and separation between the QWs in a DQW structure. When the electric field increases, the dipole moment increases due to the increasing separation between the electron and hole wave functions. On the other hand, the oscillator strength of the 11H transition is reduced as a result of the decrease in the overlap of the electron and hole envelope functions. These two competing factors give rise to optimal conditions for the enhancement of the second-order nonlinear susceptibility χ(2). It is demonstrated that χ(2) for the DQW structure is more enhanced than for the biased single QW. © 1999 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
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