Epitaxial layers of CuInTe2 on GaAs

CuInTe₂ thin films were deposited onto semi-insulating (111)A-oriented GaAs substrates by flash evaporation. Epitaxial growth was found in the substrate temperature range T_sub = 620 … 790 K. Above 750 K a second phase was found besides the chalcopyrite phase. All epitaxial films were p-type conducting and showed an increase of the hole concentration with rising substrate temperature above T_sub = 720 K. Three acceptor states with ionization energies of 350 … 500 meV, 135 … 150 meV, and of some 10⁻³ eV were found.     

Influence of source composition on the properties of flash-evaporated thin films in the Cu–In–Se system

Using CuIn₂Se_3.5 as source material epitaxial layers are obtained on (111)A- und (100)-oriented GaAs substrates by flash evaporation in the substrate temperature range T_sub = 720—870 K. The composition of the films is between CuInSe₂ and CuIn₂Se_3.5. The structural properties of the films are similar to those for CuInSe₂ epitaxial layers and refer to a chalcopyrite-like structure. The films are always p-type conducting but different acceptor states are found in dependence on the substrate temperature.     

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 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 Surface Polarity on Epitaxial Layer Growth of CuInSe2 on GaAs

CuInSe₂ thin films with thicknesses of about 0.1 μm were deposited onto (III) B-oriented GaAs substrates by flash evaporation. At substrate temperatures T_sub = 695–820 K the films have the chalcopprite structure with some admixture of the cubic sphalerite phase. At T_sub > 820 K only the sphalerite phase was found All the films are partly polycrystalline. From the electrical properties it follows that the films are characterized by nearly complete compensation at T_sub = 695–820 K. At T_sub = 870 K the films are p-type conducting and show two acceptor states with ionization energies of about 8 meV and 105 meV.     

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.     

Epitaxial layers of CuGaTe2 on GaAs

CuGaTe₂ thin films with thicknesses in the range from 0.1 to 0.2 μm were deposited onto semi-insulating (111) A-oriented GaAs substrates by flash evaporation under controlled growth conditions. Epitaxial growth begins at a substrate temperature of T_sub = 695 K. In the range T_sub = 695 … 820 K the films have the chalcopyrite structure, at T_sub = 820 to 840 K a second phase was observed besides the chalcopyrite phase. At T_sub > 840 K the films become polycrystalline. All epitaxial films were p-type conducting and showed an increase of the hole concentration with rising substrate temperature. The measured mobilities indicate to the presence of a high concentration of neutral impurities or defects.     

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.     

Deposition of InP on GaAs Substrates in the InP/PCl3/H2 System

Vapour phase epitaxial layers of InP were deposited onto (111)A-, (111)B-, (001)-, and (110)-oriented GaAs substrates in the InP/PCl₃/H₂ system using a close-space technique. It is shown that the dependence of the layer quality on the substrate orientation is due to differences in the initial growth stages. Results on the growth rates and the electrical properties of the layers are reported.     

Growth behavior of CuPc films by physical vapor deposition

Various Cu‐phthalocyanine (CuPc) films were grown from physical vapor deposition on top of indium‐tin‐oxide glass substrates by controlling substrate temperature (T_sub), source temperature (T_sou), and growth time. From side‐view SEM pictures, the growth rates for these CuPc films are estimated and can be categorized into three regions. From the Arrhenius plot of growth rate versus 1/T_sub, the activation energy E_A can be obtained. As T_sou = 390 °C, for region (A) with T_sub < 140 °C, the growth of CuPc films is dominated by the adhesion process with E_A = 810 meV. For region (B) with 140 °C < T_sub < 320 °C, the growth is then limited by the steric character associated with the organic molecular solids with E_A = 740 meV. For region (C) with T_sub > 320 °C, the re‐evaporation of the CuPc adhered molecules from the interface becomes dominant. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth,structure, and stoichiometry of epitaxial Cu-III-VI2 films on CaF2 substrates

Thin films of CuInTe₂, CuInSe₂, CuInS₂, CuGaSe₂ and CuGaS₂ were deposited onto (111)-and (100)-oriented CaF₂ substrates by flash evaporation technique. Epitaxial growth occurs at substrate temperatures in the range from 750 to 900 K, dependent on the kind of film material. Contrary to the case of GaAs, GaP and Ge substrates there are always polycrystalline parts. The layers were found to be single phase and crystallizing in the chalcopyrite structure only. The composition of the films varied in dependence on the substrate temperature. In the range of about 700 K a nearly stoichiometric composition was found.     

RHEED Measurements of AgGaSe2 thin films flash evaporated onto {111} a-GaAs

AgGaSe₂ thin films were prepared by flash evaporation on {111} A-oriented GaAs substrates and investigated by reflection high energy electron diffraction (RHEED). Epitaxial growth takes place in the substrate temperature interval of T_s = 845–920 K. The azimuthal orientation of the deposit on the substrate is discussed, supposing a AgGaSe₂ c/a ratio of 1.82. It is shown that detection of twin formation in the films is possible from RHEED measurements in the <211>-azimuths with respect to the substrate.     

Investigations of LiInSe2 Epitaxial Layers on {100}- and {110}-oriented Substrates with Sphalerite Structure by Means of RHEED

Epitaxial LiInSe₂ films were deposited by flash evaporation technique on {100}, {110} GaAs and {100} GaP. By means of geometrical considerations based on the concept of corresponding substrate and deposit planes epitaxial relationships can be predicted and compared with results from reflection high energy electron diffraction (RHEED). The epitaxial relationships are given for both rhombic (β-NaFeO₂-type) and tetragonal (chalcopyrite-type) LiInSe₂ deposits on {100}- and {110}-oriented sphalerite-type substrates.     

MOVPE growth of spontaneously ordered (GaIn) and (AlIn)P layers lattice matched to GaAs substrates

A systematic study of the metal-organic vapour-phase epitaxial growth of (GaIn)P and (AlIn)P layers deposited on GaAs substrates with (001) and (110) orientation is presented. Special attention has been paid to the growth on (001)-oriented wafers with different misorientations to the growth direction. The influence of the growth conditions on the properties of the epitaxial layers such as lattice mismatch, alloy composition, photoluminescence (PL) wavelength, FWHMs of PL peaks and atomic ordering is discussed. Layers with mirrorlike surfaces and various degrees of order could be deposited at growth temperatures T_g ranging from 595 °C to 750 °C for (GaIn)P and 720 °C to 800 °C for (AlIn)P. In addition to the influence of T_g on the Ga incorporation during the (GaIn)P growth we found the Ga distribution coefficient k_Ga to be affected by the misorientation of the substrates. k_Ga correlates presumably with the number of kinks and steps on the substrate surface. Transmission electron diffraction (TED) and PL investigations show that the degree of order — often described by the ordering paramter η — depends strongly on T_g the ordering is more pronounced when the layers are deposited on substrates misoriented towards the (1 11) lattice plane. Strong ordering has been observed for (GaIn)P samples grown at 680 °C on substrates 2° misoriented towards the [1 10] direction and at 650 °C on substrates 6° misoriented towards the same direction. For the (AlIn)P samples striking ordering has been found when they were grown at 720 °C.     

Effektive Masse und Beweglichkeit der Löcher in p-ZnSiAs2

The density of states effective mass of the valence band and impurity parameters in p-ZnSiAs₂ were determined from the temperature dependence of the Hall coefficient. The density of states effective mass of holes in ZnSiAs₂ is (0.21 ± 0.03) m₀. Three acceptor levels located at 15 meV, 40 meV and 200 meV upper the valence band edge were found. A mobility analysis was carried out taking into account the interaction of the current carriers with the large number of longitudinal optical branches existing in chalcopyrite structure. The experimental values are in good accordance with the theoretical mobility curves in the temperature range from 77 K up to 600 K.     

The influence of the lattice misfit on the growth of CuGaSe2 Epitaxial Films on {100}-oriented GaAs and GaP Substrates

CuGaSe₂ epitaxial layers were prepared on GaAs and GaP {100}-oriented substrates by flash evaporation technique and characterized by RHEED. Different epitaxial relationships have been found for growth on the different types of substrate material. The orientation is determined by the minimum misfit.     

Optical properties of Ga1–xInxAs LPE-layers and p-n structures

The multiple layer structure nGaAs(n Ga_1–xIn_xAs) p Ga_1–xIn_xAs (0 ≦ × ≦ 0.18) was realized by liquid phase epitaxy from In–Ga–As-melts on (111)-oriented GaAs substrates. The InAs-content of the mixed crystal layers was found to be dominating for crystal perfection and growth rate. The cathodoluminescence spectra of p-and n-type Ga_1–xIn_xAs and spectral distribution of the electroluminescence from pn-junctions were measured at T = 77 K and 300 K. The external quantum efficiency wa found to have a maximum for diodes with x ≈ ≈ 0.006. This is caused by the decrease of the optical absorption with increasing x and increasing dislocation density on the other hand.     

Characterization of nanocrystals in laser condensates deposited through vanadium evaporation in an oxygen atmosphere

The influence of the substrate temperature T _sub (20–360°C) and the oxygen pressure P(O₂) (5 × 10⁻³−0.13 Pa) in an evaporation chamber on the structure and phase composition of films prepared through laser sputtering of a vanadium target is investigated by electron diffraction and in situ transmission electron microscopy (with the use of the bend extinction contour technique for determining the bending of the crystal lattice). It is demonstrated that the oxygen content in the films increases with an increase in the oxygen pressure P(O₂) at a fixed substrate temperature T _sub and decreases with an increase in the substrate temperature T _sub at a fixed oxygen pressure P(O₂). The conditions responsible for the formation and composition of the crystalline (VO_0.9) and amorphous (V₂O₃) phases in the films are determined. It is established that the phase composition of the film depends on the angle of condensation of the vapor-plasma flow. The crystallization of the V₂O₃ amorphous phase is accompanied by an increase in the density by 9.2%. It is revealed that the V₂O₃ spherulites growing in the amorphous film have a bent crystal lattice. The bending of the crystal lattice can be as large as ∼42 deg/μm.

     

Crystallographic defects in epitaxial layers of cadmium sulphide

Thin epitaxial films of CdS deposited in high vacuum on ionic single crystal substrates have been studied by transmission electron microscopy. The (100), (110) and (111) faces of NaCl and the (111) face of BaF₂ were used as substrate surfaces. Both cubic sphalerite and hexagonal wurtzite structure films have been produced. The orientations of the sphalerite structure films were (100) and (110) and were produced on substrate faces having the same two orientations. The wurtzite structure films were in (0001) orientation and grew on (111) oriented substrate faces. For a fixed rate of deposition both the number and type of defects found in the films appear to be dependent upon the growth temperature and the crystal structure. Annealing the films at a high temperature has been tested as a means for reducing their defect content and the effect is very different for the two crystal structures. A reduction in the defect content of the wurtzite structure films is induced but no change in the crystal structure occurs. In contrast to this, the sphalerite structure films undergo a progressive phase transformation to the wurtzite stucture while at the same time losing a high proportion of their defects.     

Growth condition related orientation transition for YBa2Cu3O7−δ films on NdGaO3 substrate

For comprehensive understanding, the crystallographic out-of-plane axis transition for YBa₂Cu₃O_7?δ (YBCO or Y123) films grown on (110) NdGaO₃ (NGO) substrate, using liquid phase epitaxy (LPE), was systematically investigated via changing flux composition, processing temperature and oxygen partial pressure. It is found that LPE films could grow, remarkably, in a wide temperature range between 24 K above and 25 K below the peritectic temperature (T_p). The unpredicted c-oriented films formed at the temperatures above T_p, is deduced to be attributed to the etch-back behavior, i.e., Nd partially dissolved from the NGO substrate into solution, which leads to a locally high supersaturation for facilitating film growth. Even more distinctively, decreasing from the high temperature in this wide range, the YBCO films characteristically experienced the orientation transitions, the double transition of the c-axis oriented→a/c-axis mixed→c-axis oriented in air, and a single evolution of the c-axis→a-axis in the pure oxygen atmosphere. By combining supersaturation with the NGO etch-back, and solute diffusion, the transition origin of the film orientation in various temperature regions was clarified.