Hot Wall Epitaxy Method Research Articles

The growth of PbTe on H-terminated Si( [formula omitted]) substrate by hot wall epitaxy

The PbTe films were grown on hydrogen-terminated Si(1 1 1) [H-Si(1 1 1)] substrate by the hot wall epitaxy method. These films were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and I– U measurement. The XRD spectrum revealed that PbTe films grown on H-Si(1 1 1) substrate have a preferred 〈1 0 0〉 orientation. XRD and SEM analyses showed that their crystalline quality is better than that grown on Si(1 1 1) substrates. Nucleation SEM picture shows that the growth of PbTe on Si(1 1 1) is of the Volver–Weber mode. I– U measurement indicated that n-PbTe/H–P–Si(1 1 1) heterojunction has a good junction character.

Temperature dependence of band gap and photocurrent properties for the AgInS 2 epilayers grown by hot wall epitaxy

A silver indium sulfide (AgInS 2) epilayer was grown by hot wall epitaxy method, which has not been reported in the literature. The grown AgInS 2 epilayer was found to be a chalcopyrite structure and evaluated to be high quality crystal. From the photocurrent measurement in the temperature range from 30 to 300 K, two peaks of A and B were only observed, whereas three peaks of A, B, and C were seen in the PC spectrum of 10 K. These peaks are ascribed to the band-to-band transition. The valence band splitting of AgInS 2 was investigated by means of the photocurrent measurement. The crystal field splitting, Δ cr, and the spin orbit splitting, Δ so, have been obtained to be 0.150 and 0.009 eV at 10 K, respectively. And the energy band gap at room temperature has been determined to be 1.868 eV. Also, the temperature dependence of the energy band gap, E g( T), was determined.

Growth and Photocurrent Properties for the AgInS2 Epilayers by Hot Wall Epitaxy

A silver indium sulfide (<TEX>$AgInS_2$</TEX>) epilayer was grown by the hot wall epitaxy method, which has not been reported in the literature. The grown <TEX>$AgInS_2$</TEX> epilayer has found to be a chalcopyrite structure and evaluated to be high quality crystal. From the photocurrent measurement in the temperature range from 30 K to 300 K, the two peaks of A and B were only observed, whereas the three peaks of A, B, and C were seen in the PC spectrum of 10 K. These peaks are ascribed to the band-to-band transition. The valence band splitting of <TEX>$AgInS_2$</TEX> was investigated by means of the photocurrent measurement. The crystal field splitting, <TEX>$\Delta_{cr}$</TEX> , and the spin orbit splitting, <TEX>$\Delta_{so}$</TEX> , have been obtained to be 0.150 eV and 0.009 eV at 10 K, respectively. And, the energy band gap at room temperature has been determined to be 1.868 eV. Also, the temperature dependence of the energy band gap, <TEX>$E_{g}$</TEX>(T), was determined.d.

Growth and photoconductor properties of HgCdTe epilayers grown by hot wall epitaxy method

Hg 1− x Cd x Te (MCT) was grown by hot wall epitaxy. Prior to the MCT growth, the CdTe (1 1 1) buffer layer was grown on the GaAs substrate at the temperature of 590°C for 15 min. When the thickness of the CdTe buffer layer was 5 μm or even thicker, the full-width at half-maximum values obtained from the X-ray rocking curves were found to significantly decrease. After a good quality CdTe buffer layer was grown, the MCT epilayers were grown on the CdTe(1 1 1) /GaAs substrate at various temperatures in situ. The crystal quality for those epilayers was investigated by means of the X-ray rocking curves and the photocurrent experiment. The photoconductor characterization for the epilayers was also measured. The energy band gap of MCT was determined from the photocurrent measurement and the x composition rates from the temperature dependence of the energy band gap were also obtained.

Origin of point defects in AgInS2/GaAs epilayer obtained from photoluminescence measurement

The AgInS2 epilayers with a chalcopyrite structure grown using a hot-wall epitaxy method have been confirmed to be a high quality crystal. From the optical absorption measurement, the temperature dependence of the energy band gap on AgInS2/GaAs was found to be Eg(T)=2.1365 eV−(9.89×10−3 eV)T2/(2930+T). After the as-grown AgInS2/GaAs was annealed in AgInS2/GaAs has been investigated by using the photoluminescence (PL) at 10 K. The native defects of VAg, VS, Agint, and Sint obtained from PL measurements were classified as a donors or acceptors type AgInS2/GaAs to an optical p type. Also, we confirmed that In in AgInS2/GaAs did not form the native defects because In in AgInS2 did exist in the form of stable bonds.

Effect of lattice mismatch strains on the structure and magnetic, magneto-optical properties of MnSb films on GaAs substrate

MnSb(1 0 1) thin films with different thicknesses have been successfully epitaxied on GaAs(1 0 0) substrates by the hot-wall epitaxy method. The effects of substrate-induced lattice strains on the structural, magnetic and magneto-optical properties of these films have been studied. It was found that the coercivity of the film increases (and the saturation magnetization decreases) with decreasing film thickness. Measurements of the Kerr rotation angle were made using a home-made magnetic optical Kerr effect system. The Kerr rotation angle increases with film thickness but no measurable angle is observed when the film thickness is about 27 nm. The shape of the Kerr rotation curve is found to be similar to the magnetic hysteresis loop measured by a vibrating sample magnetometer.

Observation of Discrete Energy Levels by Tunneling Spectroscopy

Tunneling spectrum observation was carried out on a Pb(Tl)Te film grown by hot-wall epitaxy method. The observed spectrum characteristics on Ag–SiO x –Pb(Tl)Te junctions reflect a series of discrete energy levels E n below the conduction band edge E c , besides the quasi localized Tl impurity states in the valence band. These discrete energy levels E n are well expressed by E n - E c =-1.6/ n 2 ( n : integer) in eV, and show quite a good consistency with the result by Esaki et al. [Esaki] From the investigation using the hydrogen-like ionization model, these donor-like deep centers seem to be realized only in such a highly degenerated p-type semiconductor with the minor n-type centers in the vicinity of surface region.

GaN epilayer on separately deposited buffer layer by hot wall epitaxy

High quality GaN epilayers were grown on a sapphire substrate using a hot wall epitaxy method. We have investigated the crystal, optical, and electrical properties of GaN epilayers grown as functions of the nitridation condition of the substrate and the growth condition of GaN buffer layer. In order to study an effective method to grow a buffer layer for the growth of high quality GaN epilayer, the buffer layers were formed on the nitridated substrate using two different methods. One is separately deposited buffer layer (SDBL), and the other is co-deposited buffer layer (CDBL). It was observed that the growth condition of the buffer layer had a strong influence on the crystal and optical properties of GaN epilayer. A strong band edge emission peak at 3.474 eV was observed from the photoluminescence spectrum measured at 5 K for GaN epilayer grown at the optimum condition of the buffer layer. The carrier concentration and mobility of undoped GaN epilayer grown with a growth rate of 0.5 μm h −1 were 2 × 10 18 cm −3 and >50 cm 3 V −1 s −1 at room temperature, respectively.

Mobility of charge carriers in double-layer PbTe/PbS structures

The method of hot-wall epitaxy is used to grow epitaxial heterostructures of p-PbTe/n-PbS on BaF2 substrates. Hall-effect measurements are analyzed in order to obtain the dependence of the effective carrier mobility on thickness and temperature in the ranges 0.1–2 µm and 100–300 K, respectively. It is found that this mobility depends on the thickness of the sample and on the individual thicknesses of its constituent layers. The effective mobility is calculated under the assumption that charge carriers are scattered by the surface of the structure and by dislocations that form at the heterojunction boundary.

Study of the band offset for [formula omitted] heterojunctions grown by hot wall epitaxy

A study of the band offset for ZnSe(100) GaAs(100) heterojunctions measured with X-ray photoelectron spectroscopy (XPS) is reported. The sample was prepared by growing ZnSe films on a GaAs(100) substrate using the hot wall epitaxy (HWE) method. X-ray diffraction (XRD) and photoluminescence (PL) spectra proved that the ZnSe epilayer is a single crystal grown along the 〈100〉 direction.

Nonstoichiometric Defects in Semiconductor SnTe Thin Films

AbstractThe mono- and polycrystalline films of the SnTe1+x semiconducting phase with controlled content of nonstoichiometric defects (NSD) were grown by thermal evaporation and hot wall epitaxy methods from the charges of different composition. The concentration of NSD was determined using X-Ray diffraction method and the measurements of carrier density. The temperature dependences of electrical conductivity and Hall coefficient were obtained in the temperature range of 77 - 300 K. The best results were obtained for hot wall epitaxy method: the perfect monocrystalline films with NSD content corresponding to x =0-0,025 and high mobility of charge carriers were grown.

Growth of CdTe/CdZnTe strained-layer single quantum wells by modified hot-wall epitaxy method and their properties

Several CdTe/CdZnTe strained-layer single quantum well (SLSQW) structures, with CdTe well width ranging from 15 to 240 Å, were grown on GaAs(100) substrates, by modified hot-wall epitaxy (HWE) method for the first time. Our HWE system is equiped with a gold tube radiation shield which is more effective in heat confinement and temperature stability than conventional metal tubes. Photoluminescence (PL) measurements of SLSQW showed that the sharp e 1h 1 excitonic transition peaks in the range of 1.597 to 1.624 eV shifted to the higher energy with decreasing well width. From the PL excitation (PLE) measurements of SLSQW, we obtained the n = 1, 2, 3 and n = 1, 2 excitonic transition peaks for the 240 and 120 Å CdTe well width SLSQW structures, respectively. The excitonic transition energies were calculated considering strain effects and this results were agreed well with experimental ones considering the exciton binding energy. Moreover, the FWHMs of excitonic transition peaks obtained from PL and PLE measurements were about 2 meV and Stokes shifts between PL and PLE spectra were about 1 meV. It indicates that the SLSQWs grown by HWE in this study have a high quality comparable to MBE-grown ones.

ホットウォールエピタキシー法によるPb&lt;SUB&gt;1&amp;minus;&lt;I&gt;x&lt;/I&gt;&lt;/SUB&gt;Ca&lt;I&gt;&lt;SUB&gt;x&lt;/SUB&gt;&lt;/I&gt;S系固溶半導体薄膜の作製と評価

Lead chalcogenide solid solution semiconductors are expected to be applied to tunable laser diodes, which operate in the mid-infrared wavelength region between 3 and 4×10−6 m ranges. The laser diode is considered to be mainly utilized to an advanced measurement system for detecting hydrocarbon pollutants in air and also to a new optical fiber communication system over super long distances, which has not been developed yet. In order to put this laser diode to practical use, it is required to operate at room temperature. In this study, we proposed a new quaternary solid solution semiconductor Pb1−xCaxS1−ySey for the cladding layer in a double-hetero or quantumn well structure laser. In our preceding study, it was revealed that the Pb1−xCaxS1−ySey semiconductor was one of the excellent materials for mid-infrared laser diodes compared with the conventional ones. Based on the result, we tryed to fabricate Pb1−xCaxS1−ySey (y=0) thin films by the hot wall epitaxy method and examined their semiconducting properties.It is expected that this laser diode with double-hetero structure has a higher operating temperature than that of the ones reported previously.

Intersubband transitions of CdTe/Cd 0.94Zn 0.06Te strained single quantum wells grown by hot-wall epitaxy

Several CdTe/Cd 0.94Zn 0.06Te strained single quantum well structures with CdTe well widths ranging from 15 to 240 Å were grown on GaAs (1 0 0) substrates by the hot-wall epitaxy method. Photoluminescence measurements on the strained single quantum well structures showed that the sharp e 1h 1 excitonic transition peaks in the range 1.597–1.624 eV were shifted to higher energy with decreasing well width. The dependence of the e 1h 1 excitonic transition energies on the CdTe well widths were calculated by taking into account the strain effects, and these theoretical values are in good qualitative agreement with the results from the photoluminescence measurements. These results indicate that the CdTe/Cd 0.94Zn 0.06Te strained single quantum wells have a good enough heterointerface with the necessary abruptness for the investigation of basic physics including optical properties.

Stress-induced mixing of light and heavy exciton states in thin films of CdTe and CdMnTe epitaxially grown on GaAs substrates

Thin crystalline films of CdTe and Cd 1- x Mn x Te with a few μm thickness have been grown on GaAs substrates by means of a hot-wall epitaxy method. Optical reflection spectra of these films at 4.2 K show the exciton doublet structures with an energy separation of a few meV due to the compressive biaxial strain. In magnetoreflection under Faraday configuration for Cd 0.984Mn 0.016Te, which shows the giant Zeeman splitting, the lower and higher energy components are assigned to be the “heavy” and “light” exciton states, respectively. At around 0.7 T the energy repulsion between the two states are observed together with the breakdown of the selection rule for circularly polarized light. With the aid of the exciton Hamiltonian given by Cho, we conclude that the strain gradient normal to the interface is most likely to mix the two states.

Photoconductivity and electrical properties of epitaxial Pb 1 − xCd xSe films

Photosensitive monocrystalline films Pb 1 − x Cd x Se ( x⩽ 0.03) of low carrier concentration ( n = 0.3 ÷ 4 × 10 17 cm −3 have been grown by hot wall epitaxy method on cleaved (111)BaF 2 or (100)KCl substrates. Photoconductive thresholds determined by spectral response measurements (at temperatures 4.2, 77 and 300 K) were in good agreement with the fundamental absorption edges and showed a large increase in the energy gap E g with Cd content. Photoconductivity in the impurity range ( hv < E g) was observed. The temperature dependence of the Hall coefficient and the mobility between 4.2 and 300 K have been studied. Temperature freeze out of the free carriers was observed. Discussion of the carrier scattering mechanisms and impurity photoconductivity phenomena is presented.

Tunneling Spectroscopy of the Band Edge Structure of SnTe

The band edge structure of SnTe has been studied by the tunneling spectroscopy. Tunneling measurements are performed between room temperature and 140 K on the epitaxial SnTe films grown by the hot wall epitaxy method. The saddle point structure near the band edge is detected in the third derivative curve of the tunneling current vs bias voltage (d 3 I /d V 3 - V ). The energy difference between the band edge and the saddle point in the conduction band is about 80 meV, and is in good agreement with the theory.

Interband transitions of ZnTe-ZnSe superlattices prepared on GaAs (100) by hot wall epitaxy

Photoluminescence measurements of ZnTe-ZnSe superlattices prepared on GaAs (100) substrates by hot wall epitaxy method were carried out. Free- and bound-exciton lines due to the interband transitions of the superlattices were observed for the first time. Absorption spectra of the reflection and the transmission modes were measured to confirm the exciton lines. A theoretical calculation based on the envelope function scheme of superlattices is presented to explain the structure dependence of the photoluminescence data, taking strain effects into account.

Investigations of the initial stage of the epitaxial growth of CdTe layers

One of the basic problems in the epitaxial growth of II–VI compounds is the high probability of twin formation caused by stacking faults. Therefore we used the method of hot-wall epitaxy, which is a special vapour deposition technique, working as close as possible to thermal equilibrium. The CdTe layers were grown on cleaved (111)-oriented or mechanically polished (311)-oriented BaF 2 substrates. The use of a special temperature programme enabled the supersaturation to be decreased and the nucleation process to be controlled. As a consequence the twin density was drastically reduced, as was clearly demonstrated using transmission electron microscopy. Comparison of the growth rates on the (111)- and (311)-oriented substrates suggests that the growth process at low supersaturation is controlled by surface kinetics.

Characterization of epitaxial films of CdTe and CdS grown by hot-wall epitaxy

Using the method of hot-wall epitaxy, layers of n-type CdTe and CdS doped with indium were grown on monocrystalline BaF 2 and SrF 2 substrates, respectively. Typical electron concentrations of up to 2 × 10 17 cm −3 in CdTe and 3 × 10 18 cm −3 in CdS were obtained. At room temperature we measured mobilities of 600 cm 2/Vs for CdTe and 230 cm 2/Vs for CdS. The mobility of some samples increased exponentially with temperature in the temperature range of 300 to 100 K. This effect can be explained by means of a grain boundary model. However, in other samples bulk scattering mechanisms play a significant role for temperatures lower than 100 K. The mobility as a function of grain size was also investigated. For the characterization of carrier traps in the CdTe films we performed deep level transient spectroscopy measurements. We found six different defect levels in the upper half of the forbidden gap. It was determined that the concentration of the defects and their distribution with depth away from the interface in heterojunction diodes were a function of the growth conditions. Using temperatures of only 350 K we were able to reduce the concentration of two of the defects in the CdTe layers.