Growth and electrical properties of epitaxial CuInS2 thin films on GaAs substrates

CuInS₂ thin films with thicknesses in the range of 500 Å were deposited onto semi-insulating (111) A-oriented GaAs substrates by flash evaporation in the substrate temperature range T_sub = 570 … 870 K. Epitaxial growth begins at T_sub = 645 K. The films had always the chalcopyrite structure. Indications to a transition from the chalcopyrite phase to the sphalerite phase were observed at T_sub = 870 K. Films grown at T_sub ≦ 800 K showed n-type conductivity whereas at growth temperatures T_sub ≧ 850 K the films were always p-type conducting. A donor level and an acceptor level with ionization energies of 0.24 eV and 0.22 eV, respectively, were found from an analysis of the electrical measurements.     

Structural and electrical properties of CuIn0.7Ga0.3Se2 epitaxial layers on GaAs substrates

Epitaxial layers of CuIn_0.7Ga_0.3Se₂ could be prepared by flash evaporation onto (111)A-oriented GaAs substrates in the substrate temperature range T_sub = 745 … 870 K. At T_sub = 745 … 820 K the films had the chalcopyrite structure, at T_sub = 820 … 845 K an additional pseudohexagonal phase was found. Indications to the presence of a sphalerite phase were found at high substrate temperatures. Films grown at T_sub ≦ 750 K were always n-type conducting and showed a largely pronounced impurity band conduction effect. At T_sub ≧ 860 K the films were always p-type conducting and two acceptor states with ionization energies of some 10⁻³ eV and of 125 … 140 meV were found.     

Influence of substrate orientation on the electrical properties of CuInSe2 epitaxial layers on GaAs substrates

The electrical properties of CuInSe₂ epitaxial layers on (111)A-, (110)-, and (100)-oriented GaAs substrates are investigated. At substrate temperatures T_sub ≧ 820 K the p-type conductivity observed is governed by an acceptor state with an ionization energy of about 110 meV independent of the substrate orientation. At T_sub ≦ 770 K three different acceptor states are found in dependence on the substrate orientation: 390 meV for (111)A-, 110 meV for (110)-, and a very shallow acceptor for (100)-oriented substrates. A possible correlation between these acceptor states and intrinsic defects is proposed.     

Suppression of phase separation in InGaN layers grown on lattice-matched ZnO substrates

Sapphire and SiC are typical substrates used for GaN growth. However, they are non-native substrates and result in highly defective materials. The use of ZnO substrates can result in perfect lattice-matched conditions for 22% indium InGaN layers, which have been found to suppress phase separation compared to the same growths on sapphire. InGaN layers were grown on standard (0 0 0 2) GaN template/sapphire and (0 0 0 1) ZnO substrates by metalorganic chemical vapor deposition. These two substrates exhibited two distinct states of strain relaxation, which have direct effects on phase separation. InGaN with 32% indium exhibited phase separation when grown on sapphire. Sapphire samples were compared with corresponding growths on ZnO, which showed no evidence of phase separation with indium content as high as 43%. Additional studies in Si-doping of InGaN films also strongly induced phase separation in the films on sapphire compared with those on ZnO. High-resolution transmission electron microscopy results showed perfectly matched crystals at the GaN buffer/ZnO interface. This implied that InGaN with high indium content may stay completely strained on a thin GaN buffer. This method of lattice matching InGaN on ZnO offers a new approach to grow efficient emitters.     

Liquid phase epitaxial growth and characterization of thin In1−xGaxAsyP1–y layers lattice-matched to InP

Growth studies enabled the deposition of In_0.71Ga_0.29As_0.68P_0.32 single quantum well structures with InP or In_0.88Ga_0.12As_0.26P_0.74 confinement layers lattice-matched to (001) InP by liquid phase epitaxy (LPE). Well widths in the order of 50–100 Å have been achieved using a conventional step cooling technique. The physical characterization has demonstrated the capability of the employed method to produce multilayered heterostructures which display confined particle states; quantum mechanically induced blue-shifts of the low temperature PL-emission up to 125 meV were measured. A remarkable reduction of the FWHM values of the shifted PL peaks was attained by optimization of the growth conditions.     

Growth of gallium antimonide epitaxial layers on indium arsenide substrates

In the present work the possibility is demonstrated of growing gallium antimonide epitaxial layers on indium arsenide substrates using the liquid phase epitaxial (LPE) method. The influence is nivestigated of the growth conditions on the morphology of the surface and interface of the epitaxial structures InAs GaSb. The optimum technological regimes for growth of heterostructures in the system InAs GaSb are found.     

A complex method for structural investigation of GaAs1−xPx epitaxial layers grown on GaAs substrates

A universal X-ray diffractometer is used for the structural complex investigation of GaAs_1−xP_x epitaxial layers, grown on the (100) face of GaAs substrate. Information is obtained from the analyses of diffraction patterns for some qualities of the epitaxial layers: crystallographical orientation, composition, thickness, as well as structure of the transition region. The suggested complex method has important advantages against the standard Laue method. It is far easier express and convenient for serial investigations.     

Influence of the graduated composition region on the properties of GaInAs epitaxial layers grown on GaAs substrates

The electrical properties of Ga_1-xIn_xAs layers (0 < x < 0.3) are investigated. The layers are grown on <111> oriented GaAs substrates. A transition layer is grown with an increasing indium content to decrease the mismatch of the lattice parameters of the substrate and the final layer. A special many-section crucible is used. In dependence on composition the decrease both of mobility and carrier concentration with the increase of compensation is observed. These facts are connected with the introducing of additional acceptors without donor concentration changes.     

Growth of ZnTe layers on (111) GaAs substrates by metalorganic vapor phase epitaxy

ZnTe layers were grown on (111) GaAs substrates by metalorganic vapor phase epitaxy using dimethylzinc and diethyltelluride as the source materials. X-ray diffraction analysis revealed that epitaxial ZnTe layers can be obtained on (111) GaAs substrates. X-ray rocking curves, Raman spectroscopy, and photoluminescence measurements showed that the crystal quality of ZnTe layers depends on the substrate temperature during the growth. A high-crystalline quality (111) ZnTe heteroepitaxial layer with strong near-band-edge emission at 550 nm was obtained at a substrate temperature of 440 °C.     

Structural and electrical properties of CuGaSe2 thin films on GaAs substrates

CuGaSe₂ thin films with thicknesses in the range of 0.1 μm were deposited onto semiinsulating (111) A-oriented GaAs substrates by flash evaporation under controlled growth conditions. Epitaxial growth begins at a substrate temperature of T_sub = 835 K. Besides the chalcopyrite phase a hexagonal modification was observed in the range T_sub = 835 to 855 K. At T_sub ≧ 860 K the films have sphalerite structure. All epitaxial films were p-type conducting. Two acceptor levels with ionization energies of about 150 meV and 550 meV, respectively, were obtained from an analysis of electrical and photoluminescence measurements.     

Structural and electrical properties of CdS thin films evaporated onto GaAs substrates

CdS thin films on GaAs substrates are prepared by single source thermal evaporation under high vacuum conditions. Films on (111)A-oriented substrates have the wurtzite structure, whereas in the case of (1 1 1 )B-oriented substrates the sphalerite structure predominates. Depositing films on pre-annealed substrates a tetragonal phase with a composition near CdGa₂S₄ was found. The electron concentration in the CdS films is influenced by the substrate temperature, the growth rate of the films, and the substrate orientation.     

Structure defects investigation of GaAs and AlxGa1−xAs epitaxial layers

The paper is concerned with the results of investigation of structure defects in gallium arsenide and Al_0.3Ga_0.7As epitaxial layers. It was found that structure defects in layers under investigation are responsible for the excess component of the Schottky diode's reverse current.     

Growth and characterization of epitaxial layers on aluminum nitride substrates prepared from bulk, single crystals

A comparative study of epitaxy of AlN, GaN and their alloys, grown on c-axis and off-axis substrates of single-crystal aluminum nitride has been carried out. Growth on off-axis (>30°) substrates appears to result in rough surfaces and the absence of two-dimensional electron gas (2DEG). However, smooth morphologies were demonstrated for both homoepitaxial and heteroepitaxial growth on on-axis (<2°) substrates. On one of these oriented substrates a 2DEG, with a mobility of 1000 cm²/V s and a sheet density of 8.5×10¹² cm⁻² at room temperature, was also demonstrated for the first time.     

Defects in epitaxial layers of silicon-germanium grown on silicon substrates

Crystal defects of various kinds found in epitaxially grown Si/Ge alloy layers on Si substrate, may be either inherent to the material and originating from atomic radii misfit, or can be traced to the growth process and controlled or eliminated by varying its parameters. A network of slip lines, becoming more pronounced with increased Ge content, indicates plastic deformation resulting from partial relief of stresses during the high temperature growth process. Electron microprobe and X-ray diffraction analysis indicate some Ge segregation in the fault vicinity, and a slight anisotropy in the lattice constant expansion due to the Ge.     

Vapour phase growth of epitaxial silicon carbide layers

After a brief overview of different epitaxial layer growth techniques, the homoepitaxial chemical vapour deposition (CVD) of SiC with a focus on hot-wall CVD is reviewed. Step-controlled epitaxy and site competition epitaxy have been utilized to grow polytype stable layers more than 50 μm in thickness and of high purity and crystalline perfection for power devices. The influence of growth parameters including gas flow, C/Si ratio, growth temperature and pressure on growth rate and layer uniformity in thickness and doping are discussed. Background doping levels as low as 10¹⁴ cm⁻³ have been achieved as well as layers doped over a wide n-type (nitrogen) and p-type (aluminium) range.

Furthermore the status of numerical process simulation is mentioned and SiC substrate preparation is described. In order to get flat and damage free epi-ready surfaces, they are prepared by different methods and characterised by atomic force microscopy and by scanning electron microscope using channelling patterns. For the investigation of defects in SiC high purity CVD layers are grown. The improvement of the quality of bulk crystal substrates by micropipe healing and so-called dislocation stop layers can further decrease the defect density and thus increase the yield and performance of devices. Due to its high growth rate functionality and scope for the use of multi-wafer equipment hot-wall CVD has become a well-established method in SiC-technology and has therefore great industrial potential.     

Electrical properties of AgGaSe2 epitaxial layers

Epitaxial layers of AgGaSe₂ with thicknesses in the range from 50 to 70 nm were deposited onto (111)A-oriented semi-insulating GaAs substrates by flash-evaporation in the substrate temperature range T_S = 825 … 900 K. Films grown at T_S ≦ 850 K are n-type conducting whereas p-type conductivity was observed at T_S ≧ 875 K. In the p-type samples two acceptor states with ionization energies of 60 and 410 meV were found from an analysis of the electrical measurements.     

Peculiarities of liquid phase epitaxy in GaInPAs/InP lattice-matched heterostructures

The temperature phase stability of Ga_xIn_1−xP_yAs_1−y solid solution has been analyzed. A simple solution theory with the temperature-independent interaction parameters in solid and liquid phases has been used. The absence of miscibility gaps for all the compositions of the solid solution, lattice-matched to InP at a growth temperature of 640°C, has been demonstrated both theoretically and experimentally. The influence of the elastic deformations on the Ga_xIn_1−xP_yAs_1−y (λ_g = 1.4 μm) solid solution parameters has been observed assuming the model of the layer coherent conjugation in heterostructures.     

Formation and properties of transition layers in epitaxial films

The current state of the problem of film-substrate transition layers in semiconductor epitaxial films is discussed. Reasons for the formation of a transition layer are considered: the influence of the substrate, the influence of the peculiarities of growth processes, and the influence of changes in the properties of the vapour phase over the growth surface. Estimates of the lattice mismatch, dislocation mobility, and impurity diffusion during growth are presented. The superimposition of size effects and the difference of estimates of a transition layer location according to data of electrophysical investigations are pointed out. Methods to remove transition layers are shown for cases of the homo- and heteroepitaxy of semiconductors.