Hot Wall Epitaxy Method Research Articles

InSb ФОТОДІОДИ (ОГЛЯД. ЧАСТИНА VI)

In this review, a brief overview of epitaxial methods of growing single-crystal InSb films and their application for the manufacture of infrared photodiodes is provided. The results of growing InSb epitaxial films on Si and GaAs substrates are described. The main attention in the review is paid to InSb/CdTe heterostructures, which is explained by the almost perfect matching of their lattices and coefficients of thermal expansion. The properties of heterovalent InSb/CdTe interfaces as promising objects for spintronics and topological insulators are described. The results of experimental studies of InSb photodiodes for the mid-wavelength region of 3-5 μm, passivated with polycrystalline CdTe films by the hot wall epitaxy method are given. To investigate the electrical properties of polycrystalline fims, the direct conductivity was measured as a function of bias voltage and temperature. For this purpose, polycrystalline fims with a thickness of 200 to 1800 nm were grown on p-InSb substrates. The type of conductivity and resistivity of polycrystalline films were determined. Conclusions were made regarding the possibility of using this technique for effective and stable passivation. Photodiodes were characterized by measuring the dark current and the lifetime of minor carriers. Properties of heterovalent CdTe/InSb and isovalent CdTe/HgCdTe interfaces are compared. It is shown that they have different effects on the transport and photoelectric characteristics of photodiodes. It was established that when the passivation layer is deposited on the chemically etched surface of the mesa, an excess current of tunneling nature occurs in the photodiodes. The best results were obtained when surface treatment of the mesa includes the use of CP4A and HCl etchants, sulfidization in a non-aqueous Na 2 S solution, and deposition of a CdTe protective layer. Passivation of HgCdTe photodiodes using polycrystalline CdTe films does not affect the lifetime of charge carriers, but it needs improvement to achieve better stability of their characteristics.

Development of epitaxial PbS layers obtaining method for photoelectric transducers

Photoelectric transducers are a semiconductor device that converts photonic energy into electrical energy. This paper describes obtained by the hotwall epitaxy method epitaxial PbS layers technology. Materials, methods, technological parameters of synthesis were selected and substantiated. A theoretical model of the p-n transition has been developed. The calculation of the main parameters has been done. The hotwall epitaxy method was chosen for the synthesis, because it allows to obtain layers with required properties in a single technological cycle with an economical consumption of material. BaF2 was chosen as the substrate, because in this case a smaller difference in the identity periods and the layer and the substrate thermal expansion coefficients is achieved.

Forming of CdZnTe thin films grown by hot wall epitaxy and their properties

In this work morphological, X-ray structural and optical studies of CdZnTe films grown by hot wall epitaxy method at relatively low substrate temperatures were performed. Possible mechanisms and processes of self-organization that occur during the growth of such structures are considered. It is shown that at thickness of film more than 130 nm on the surface, large (lateral size 150 - 200 nm, height - up to 10 nm) and small crystals are observed. The thicknesses and energy of the band gap width of the CdZnTe films grown at different growth times were determined. It is shown that the film absorption edge in the transmission spectra depends on the film thickness and the reasons for the shift of the film absorption edge are discussed.

HgCdTe/CdZnTe LPE epitaxial layers: From material growth to applications in devices

Some properties of liquid phase epitaxy growth of Hg1-xCdxTe/Cd1-yZnyTe epiwafers (x ≈ 0.21; 0.3 and y ≈ 0.04 by mole fraction) applicable for mid- and long wavelength infrared (IR) photodiodes and focal plane arrays (FPA) are described. The design and technology of infrared photodetectors manufacturing, both single and multielements arrays with different sizes of sensitive elements, have been developed. Experimentally determined are the low-temperature regimes (T ≤ 100 °C) of CdTe passivation layers growth by hot wall epitaxy method and regimes of thin metallic contact layers deposition by vacuum thermal and magnetron sputtering techniques. From measured current-voltage characteristics of formed HgCdTe photodiodes with area ~(0.4–0.8) × 10−4 cm2 the value of detectivity was estimated as D* = 2.67·1010 cm·W−1·Hz1/2 for long wavelength photodiodes. NETD for 320x256 mid IR FPAs with junction area 10 × 10 µm2 and pitch 20 µm was 15–22 mK.

Constituent substitution in hot wall deposition of Bi2S3 films by reaction with substrates

Replacement of a constituent in the overgrown layers with the materials provided by the substrates is investigated when Bi2S3 films are deposited on III-V compound semiconductors and transition metals using a hot wall epitaxy method. The substitution caused by the S atoms is stronger than that by the Se and Te atoms in deposition of Bi2Se3 and Bi2Te3 films. Mere exposure to Bi2S3 vapor of In-containing compounds (InP and InAs) and Ga-containing compounds (GaAs and GaSb) at epitaxial growth temperatures results in a capping of their surfaces by In2S3 and GaS, respectively. A temperature window is revealed to exist for the GaAs case where growth of Bi2S3 microcrystals occurs within the temperature range for the sulfide formation. The sulfurization by the material substitution is thus demonstrated to be not always identical with that using elemental sulphur. We examine furthermore the sulfides synthesized on the surfaces of Cu, Ag, Ni, Mo, and W. The sulfides produced on Cu and Ag undergo material alterations when they are irradiated by a laser light.

Quasi-Chemistry of Intrinsic Point Defects in Cadmium Telluride Thin Films

The defect formation in cadmium telluride thin films when growing from the vapor phase by a hot-wall epitaxy method has been described with the help of quasi-chemical reactions. The analytical expressions of the dependences of concentration of free charge carriers and dominant intrinsic atomic defects on the technological factors (substrate temperature тS, evaporation temperature тE and partial vapor pressure of cadmium ) have been obtained. It has been shown that the concentration of free charge carriers in CdTe films is determined by vacancies of cadmium and tellurium.

Growth of CaAl2Se4: Co Single Crystal Thin Film for Solar Cell Development and Its Solar Cell Application

After the CuInSe₂films grown by hot-wall epitaxy method were annealed in Cu-, Se- and In-atmospheres, the point defects were investigated by using the photoluminescence (PL) experiment. In the as-grown CuInSe₂films, the free excitons corresponding to the light hole and the heavy hole have been observed, and their splitting gap was 8.2 meV. The gap is associated with the strain caused by the lattice mismatch between the substrate and the film in the heterojunction growth. By means of thermal annealing in various atmospheres, the (D˚, X) emission was observed to originate from the Vse or CUint. From this emission, the ED value of the donor impurity level is extracted to 0.1950 eV. Also, the emission between the free electrons and the acceptor holes (FA) became a dominant peak after Se atmosphere treatment, and the EA value of the acceptor level is turned out to be 0.2371 eV. Thus, the origin of the FA emission is related to Vcu or Seint. These PL results led us to confirm that CuInSe₂:Se is converted into the optical n-type. In addition, the origin of the donor-acceptor pair emissions is caused by the recombination between donors such as Vse or CUint and acceptors such as Vcu or Seint. Based on these PL results, we have schemed a new energy-level diagram of the recombination process in CuInSe₂.

Invariance of multifractal spectrums of spatial forms on the surface of ZnxCd1-xTe – Si heterocompositions synthesized by electron beam epitaxy and hot wall epitaxy

Multifractal (MF) analysis is applied for the description of spatial nanoforms which form a relief on a surface of heterostructures of ZnxCd1-xTe solid solution – substrate Si (111) synthesized by the method of the electron beam with the evaporating anode. The input data for the MF analysis were the AFM (atomic force microscopy) images of the surface of layers. Comparison of parameters of MF spectrums for different geometries of the surface relief of the layers obtained at identical temperatures and approximately identical growth rates by the above mentioned method of growth and the method of hot wall epitaxy has been performed.It was shown that within the error limits, MF spectrums of spatial nanoforms for heterostructures ZnxCd1-xTe – Si remained very similar under identical conditions for synthesis of layers for compared techniques.

Hot-wall-epitaxy growth and electrical/optical characterization of epitaxial BaAl2S4/GaAs layers

The BaAl2S4 layers, which were identified to be a cubic structure in space group Pa3, were grown using the hot wall epitaxy method attached with the reservoir tail. Also, the coincidence lattice mismatch of the grown layers was shown to be −2.52% due to the influence of the compressive strain. The Hall effect measurement showed the different temperature-dependent decrease of mobility at a temperature above 100K. One was T−1/2 at the temperature range of 100<T<180K and the other was T−3/2 at the temperature of T>180K. The mobility decreased in proportion to T1 at a low temperature range of T<100 K. Three PC peaks obtained from the photocurrent (PC) spectra were corresponding to band-to-band transitions, which were observed over the temperature range. These PC peaks were caused by the transition of electrons from the three valence band states in order of increasing energy to the conduction band states, respectively. By analyzing absorption and PC results, the band gap variation has been compared and matched well with Eg(T)=Eg(0)−7.556×10−4T2/(T+523), where Eg(0) is estimated to be 4.0596, 4.1053, and 4.1094eV.

The composition and the structure of thin films based on metal porphyrin complexes

Thin films based on CuTPP, ZnTPP and FeClTPP (ТРР – TetraPhenylPorphyrin) complexes and manufactured by vacuum deposition under quasi-equilibrium conditions have been investigated. The hot-wall epitaxy method was chosen for the preparation of samples. The structure of objects and their composition were examined by scanning electron microscopy (SEM) and energy dispersive microanalysis (EDX). The CuTPP film was established to form whiskers about 20nm in diameter and 5µm in length. The structural features and morphology of ZnTPP and FeClTPP films’ surface were revealed. The theoretical interpretation of obtained results was proposed that made it possible to relate the film structure with its composition.

Growth and Hall-effect/photocurrent analysis on BaAl2Se4 layers grown by hot wall epitaxy method

The epitaxial growth of photoconductive BaAl2Se4 layers, which have a tetragonal structure, was first achieved through the hot wall epitaxy method. From the Hall effect result, in the high temperature range of T>230K, the mobility decreased as a function of T−3/2 and its scattering was mainly due to the acoustic phonon mode of lattice vibrations through a deformation potential. Thus, at the intermediate temperature range (100<T<230K), the mobility gradually decreased as a function of T−1/2. This behavior was attributed to the piezoelectric potential scattering. In contrast, the mobility decreased in proportion to T1 in a low temperature range of T<100K and its decrease was caused by dislocation scattering. Through the relationship between the reciprocal temperature and the carrier concentration, three donor levels were found to be 0.3, 14.7, and 95.3meV below the conduction band. From the photocurrent (PC) spectra, three PC peaks A, B, and C corresponding to band-to-band transitions were observed at all temperatures. According to the selection rule, the crystal field and spin orbit splitting were found to be 0.2029 and 0.2154eV, respectively, through the direct use of PC spectroscopy. Based on the analysis of optical absorption and PC spectra, the optical band gap was well expressed by Eg(T)=Eg(0)−4.39×10−4T2/(T+250), where Eg(0) is estimated to be 3.4205, 3.6234, and 3.8388eV for the transitions corresponding to the valence band states Γ3(A), Γ4(B), and Γ5(C), respectively.

GROWTH AND MICROSTRUCTURES OF ULTRATHIN Bi2Te3 NANOPLATES BY MODIFIED HOT WALL EPITAXY

Ultrathin Bi 2 Te 3 nanoplates have been grown on an oxidized silicon substrate by a modified hot wall epitaxy (HWE) method, in which a quartz plate with holes was employed. The microstructures and optical properties of Bi 2 Te 3 nanoplates were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscope (AFM) and micro-Raman spectroscopy. The results show that ultrathin Bi 2 Te 3 nanoplates with the thickness of about six quintuple layers (QLs) are obtained, which is difficult for the traditional HWE technique. The Raman vibration mode [Formula: see text] from the nanoplates exhibits an obviously red shift with decreasing thickness. The thickness variation of one nanoplate was obtained by the Raman map derived from the vibration frequency of [Formula: see text] mode and is in good agreement with the AFM result, which indicates that Raman map is an effective method to characterize the thickness difference of ultrathin Bi 2 Te 3 nanoplates.

Growth and photocurrent characteristics of the photoconductive MnAl2S4 layers grown by hot-wall epitaxy method

The epitaxial growth of the photoconductive MnAl2S4 with a layered-type rhombohedral structure was first achieved by means of the hot-wall epitaxy method. From the Hall effect measurement, two dominant scattering mechanisms on the mobility were extracted. One was an acoustic phonon scattering caused by lattice vibrations at the high-temperature range of T>100K and the other one was an impurity ion scattering at the low-temperature range of T<100K. Also, from the relation between the reciprocal temperature and the carrier concentration, two activation energies were evaluated to be the deep level of 83.1 and a shallow level of 14.1meV at high-temperature and middle-temperature ranges, respectively. From the photocurrent (PC) measurement, the A, B, and C peaks were observed at whole temperature range. The electronic origin of these three peaks were caused by the band-to-band transitions from the valence band states of Γ4(z), Γ5(x), and Γ5(y) to the conduction band state of Γ1(s), respectively. Thus, the parameters of the crystal-field and the spin–orbit splitting were directly extracted by means of PC spectroscopy, and those values were 3.5 and 39.9meV, respectively. The band gap energies estimated from PC and absorption measurements were well expressed by Eg(T)=Eg(0)−2.80×10−4T2/(T+287), where Eg(0) were found to be 3.7920, 3.7955, and 3.8354eV at the valence band states of Γ4(z), Γ5(x), and Γ5(y), respectively.

Surface states of charge carriers in epitaxial films of the topological insulator Bi2Te3

The galvanomagnetic properties of p-type bismuth telluride heteroepitaxial films grown by the hot wall epitaxy method on oriented muscovite mica substrates have been investigated. Quantum oscillations of the magnetoresistance associated with surface electronic states in three-dimensional topological insulators have been studied in strong magnetic fields ranging from 6 to 14 T at low temperatures. The cyclotron effective mass, charge carrier mobility, and parameters of the Fermi surface have been determined based on the results of analyzing the magnetoresistance oscillations. The dependences of the cross-sectional area of the Fermi surface S(kF), the wave vector kF, and the surface concentration of charge carriers ns on the frequency of magnetoresistance oscillations in p-type Bi2Te3 heteroepitaxial films have been obtained. The experimentally observed shift of the Landau level index is consistent with the value of the Berry phase, which is characteristic of topological surface states of Dirac fermions in the films. The properties of topological surface states of charge carriers in p-type Bi2Te3 films obtained by analyzing the magnetoresistance oscillations significantly expand fields of practical application and stimulate the investigation of transport properties of chalcogenide films.

Growth and electrical/optical properties of the photoconductive ZnAl2Se4 layers grown by hot wall epitaxy method

Growth and electrical/optical properties of the photoconductive ZnAl2Se4 layers grown by hot wall epitaxy method

뜨거운 곁쌓기 법에 의해 성장된 MgGa2Se4단결정 박막의 열처리 효과

The evaporating materials for single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, compounded polycrystal powder was deposited on thoroughly etched semi-insulated GaAs(100) substrate by the hot wall epitaxy (HWE) method system. The source and substrate temperatures of optimized growth conditions, were and , respectively.The source and substrate temperatures were and , respectively. The crystalline structure of the single crystal thin films was investigated by double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the obtained from the absorption spectra was well described by the Varshni`s relation, $E_g(T)

Surface Oxidation Properties in a Topological Insulator Bi2Te3 Film

Bi2Te3 films are grown on (111)-oriented GaAs substrates by using the hot wall epitaxy method and the surface oxidation properties in the films are investigated by x-ray photoelectron spectroscopy, Raman spectroscopy, and x-ray diffraction. The results show that the films are c-axis oriented. Two pairs of new peaks in the XPS spectra involved with the binding energies from Bi 4f and Te 3d electrons correspond to Bi—O—Te bonds. Besides the A11g, E2g and A21g vibration modes from Bi2Te3 films, two new peaks at 93.5cm−1 and 123cm−1 are observed in Raman spectra, which are assigned to α-Bi2O3 and TeO2, respectively. Our results are helpful for analyzing the degradation mechanism of topological surface states in Bi2Te3.

Growth and electrical/optical characteristics of unintentional p-type BaIn2Se4 epilayers grown using hot wall epitaxy method

The epitaxial growth of photoconductive BaIn2Se4, which has orthorhombic structures, was first achieved through the hot wall epitaxy method. The electrical and optical characteristics of these epilayers were discussed. From the Hall effect measurement, in a high-temperature range of T>150K, the mobility decreased as a function of T−1 and its scattering was mainly due to the acoustic phonon mode of lattice vibrations through a deformation potential. In contrast, the mobility decreased in proportional to T0.6 in a low-temperature range of T<150K and its decrease was caused by the impurity ion scattering. Also, from the relation between the reciprocal temperature and the carrier concentration, two dominant levels 136.9 and 27.9meV were extracted out and they were estimated to be the activation energies of the shallow acceptor levels caused by the native defects of the upper edge of the valence band. In addition, from the optical absorption measurement, the bandgap variation of BaIn2Se4 epilayers extracted was well expressed by Eg(T)=2.626eV–4.99×10−3T2/(T+559).

Behavior of temperature-dependent photoresponse in unintentional p-type BaIn2Se4 layers through photocurrent spectroscopy

Temperature-dependent photocurrent (PC) behavior of unintentional p-type BaIn2Se4 layers grown through the hot wall epitaxy method has been investigated. From the PC measurement, three peaks A, B, and C corresponded with the intrinsic transitions from the valence band states of Γ3(A), Γ4(B), and Γ5(C) to the conduction band state of Γ1, respectively. The interval on the valence band splitting of the crystal field and the spin orbit splitting was observed to be 0.0903 and 0.1507 eV, respectively. The temperature dependence of the optical bandgap energy could be well expressed by using Varshni's formula: Eg(T) = Eg(0) − αT2/(β + T), where α and β are taken to be 4.96 × 10−3 eV/K and 554 K, respectively. Also, the Eg(0) was estimated to be 2.6262, 2.7165, and 2.8672 eV at the valence band states of Γ3(A), Γ4(B), and Γ5(C), respectively. However, the PC intensities decreased with lowering temperature. In the log Jph vs 1/T plot, the dominant level at the high-temperature region was observed and its value was 29.1 meV. This level corresponds to the activation energy for the electronic transition from the edge of the valence band to the shallow acceptor levels caused by these native defects. Consequently, we suggest that the trapping centers due to native defects in BaIn2Se4 layers are responsible for this PC-intensity decrease with decreasing temperature.

Structural, electric, and optical properties of MgGa2Se4 epilayers grown by hot wall epitaxy method

The epilayer growth of the MgGa2Se4 compounds was successfully achieved through the hot wall epitaxy method. The grown layer was accumulated along the <116> direction onto the GaAs(100) substrate. From the Hall effect measurement, the mobility was determined to be 264cm2/Vs at 293K. At a high temperature range (T>150K), it tended to decrease as a function of T−3/2 by increasing the temperature, and increase as a function of T3/2 at the low-temperature range (T<100K). In the photocurrent (PC) measurement, we observed the A, B, and C peaks corresponding to 529.9 (2.3398eV), 495.2 (2.5037eV), and 477.6nm (2.5960eV) at 10K, respectively. Three peaks of A, B, and C were caused by the band-to-band transitions from the valence band state of Γ4(z), Γ5(x), and Γ5(y) to the conduction band state of Γ1(s), respectively. By comparing the results of PC and absorption, the temperature dependence of the optical bandgap energy was well interpreted using Varshni's relation Eg(T)=2.3412−8.87×10−4T2/(T+251).