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.     

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.     

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 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.     

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.     

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)     

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.     

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.     

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.

     

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.     

Dielectric properties of betaine phosphite and deuterated betaine phosphite films

Polycrystalline films of betaine phosphite (BPI) and deuterated BPI have been grown by evaporation on LiNbO₃, α-SiO₂, α-Al₂O₃, and NdGaO₃ substrates. These films consist of large single-crystal blocks in which the polar axis (b) lies in the substrate plane. The results of studying the dielectric properties of the films using interdigital electrodes, X-ray diffraction, and block images in a polarized-light microscope in reflection are reported. The film transition into the ferroelectric state at T = T _c is accompanied by strong anomalies of the capacitance of the film/interdigital structure/substrate structure. The deuteration of BPI films leads to an increase in their temperature T _c: from T _c = 200 K for BPI-based structures to T _c = 280 K for structures with a high degree of deuteration (d ∼ 90%).     

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.     

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.     

Influence of the substrate temperature on the structural,optical, and electrical properties of tin selenide thin films deposited by thermal evaporation method

Thin films of tin selenide (SnSe) were deposited on sodalime glass substrates, which were held at different temperatures in the range of 350‐550 K, from the pulverized compound material using thermal evaporation method. The effect of substrate temperature (T_s) on the structural, morphological, optical, and electrical properties of the films were investigated using x‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission measurements, and Hall‐effect characterization techniques. The temperature dependence of the resistance of the films was also studied in the temperature range of 80‐330 K. The XRD spectra and the SEM image analyses suggest that the polycrystalline thin films having uniform distribution of grains along the (111) diffraction plane was obtained at all T_s. With the increase of T_s the intensity of the diffraction peaks increased and well‐resolved peaks at 550 K, substrate temperature, were obtained. The analysis of the data of the optical transmission spectra suggests that the films had energy band gap in the range of 1.38‐1.18 eV. Hall‐effect measurements revealed the resistivity of films in the range 112‐20 Ω cm for films deposited at different T_s. The activation energy for films deposited at different T_s was in the range of 0.14 eV‐0.28 eV as derived from the analysis of the data of low‐temperature resistivity measurements. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of annealing temperature on the structural and optical properties of amorphous Sb2Te2Se thin films

Thin films of Sb₂Te₂Se were prepared by conventional thermal evaporation of the presynthesized material on Corning glass substrates. The chemical composition of the samples was determined by means of energy‐dispersive X‐ray spectrometry. X‐ray diffraction studies on the as‐deposited and annealed films revealed an amorphous‐to‐crystalline phase transition. The as‐deposited and annealed films at T _a = 323 and 373 K are amorphous, while those annealed at T _a= 423 and 473 K are crystalline with a single‐phase of a rhombohedral crystalline structure as that of the source material. The unit‐cell lattice parameters were determined and compared with the reported data. The optical constants (n , k ) of the investigated films were determined from the transmittance and reflectance data at normal incidence in the spectral range 400–2500 nm. The analysis of the absorption spectra revealed non‐direct energy gaps, characterizing the amorphous films, while the crystalline films exhibited direct energy gaps. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Infrared optical properties of Cu1−xLixSe2 thin films

Infrared absorption spectra of Cu_1−xLi_xInSe₂ thin films are measured at room temperature in the wavenumber range from 100 to 600 cm⁻¹. The spectra exhibit two absorption bands in the wavenumber ranges 200–210 cm⁻¹ and 330–355 cm⁻¹ which are ascribed to vibrational modes due to In Se and Li Se vibrations, respectively. The influence of the phase transition from the chalcopyrite structure to the β-NaFeO₂ structure in the composition range x = 0.5–0.6 on the vibrational characteristics is established and discussed.     

Substrate temperature dependence of microcrystalline silicon growth by PECVD technique

Undoped hydrogenated silicon films have been prepared from a gas mixture of silane and hydrogen, varying substrate temperature from 180–380 °C in an ultrahigh vacuum system using RFPECVD technique. XRD and Raman measurements enable us to know that the films are microcrystalline throughout the substrate temperature range. Bond formation of the SiH films at different substrate temperature is studied through different characterisation techniques like Fourier transform infrared spectroscopy and hydrogen evolution study. The infrared absorption spectroscopy and hydrogen evolution study reveal two types of growth: the formation of a void rich material at low T_s (∼180 °C) and a compact material at comparatively higher T_s.     

Invar effect in PbFe<Subscript>1/2</Subscript>Nb<Subscript>1/2</Subscript>O<Subscript>3</Subscript> ceramics

High-density lead ferroniobate PbFe_1/2Nb_1/2O₃ (PFN) is prepared by conventional ceramic technology. Its structural properties are studied in a wide temperature range (293 ≤ T ≤ 973 K). The following chain of phase transitions is established in the vicinity of the transition to the polar phase: Rh (rhombohedral phase) (T < 363 K) → Psc (pseudo-cubic phase) (363 < T < 387 K) → C (cubic phase) (T > 387 K). The paraelectric range contains five ranges of constant unit-cell volume (invar effect): I (387 ≤ T ≤ 413 K), II (433 ≤ T ≤ 463 K), III (553 ≤ T ≤ 613 K), IV (743 ≤ T ≤ 773 K), and V (798 ≤ T ≤ 823 K). It is shown that the anomalous behavior of the PFN dielectric characteristics above the Curie temperature, which was revealed previously, is associated with the specific features of its real (defect) structure, which is caused by the crystal-chemical specificity of the main structure-forming agents: α-Fe₂O₃ and α_ht-Nb₂O₅.     

Cd‐Doping Effects on The Properties of Polycrystalline α‐In2Se3 Thin Films

The X‐ray diffraction has revealed that the polycrystalline hexagonal structured α‐In₂Se₃ thin films grown at substrate temperature of 200 °C with the unit cell parameters a = 4.03 Å and c = 19.23 Å becomes polycrystalline hexagonal structured InSe with a unit cell parameters of a = 4.00 Å and c = 16.63 Å by Cd‐doping. The analysis of the conductivity temperature dependence in the range 300‐40 K revealed that the thermionic emission of charged carriers and the variable range hopping are the predominant conduction mechanism above and below 100 K, respectively. Hall measurements revealed that the mobility is limited by the scattering of charged carriers through the grain boundaries above 200 K and 120 K for the undoped and Cd‐doped samples, respectively. The photocurrent (I_ph) increases with increasing illumination intensity (F) and decreasing temperature up to a maximum temperature of ∼100 K, below which I_ph is temperature invariant. It is found to have the monomolecular and bimolecular recombination characters at low and high illumination intensities, respectively. The Cd‐doping increases the density of trapping states that changes the position of the dark Fermi level leading to the deviation from linearity in the dependence of I_ph on F at low illumination intensities.