Hot Wall Beam Epitaxy Research Articles

An in situ spectrochemical study of the reduction of thin fullerene films

The reduction of thin fullerene films has been investigated in the presence of different cations in acetonitrile using cyclic voltammetry and in situ attenuated total reflection FTIR spectroscopy. Solution cast and hot wall beam epitaxy films of C 60 were studied in a three-electrode spectroelectrochemical cell, using a reflection element of germanium covered with platinum as the working electrode. The cyclic voltammetric response is highly dependent on the preparation method of the film and on the electrolyte solution. The infrared spectral changes observed during the reduction processes of C 60 films show the formation of different reduction states depending on the electrolyte. In the case of Li +, K + and TBA + containing electrolytes C 60 2− is obtained either in one or in two steps. With Na + only C 60 − is found. In the case of Rb +, mixed reduction states 1–4 are found. The IR bands during electrochemical reduction in Rb + containing electrolyte solution do not indicate the electrochemical formation of the stable RbC 60 polymeric phase as obtained by vapour doping with Rb.

GaN and InGaN prepared by hot wall beam epitaxy

GaN and InGaN epilayers were successfully obtained on nitrided Ga buffer layers predeposited on the sapphire (0001) substrate by Hot Wall Beam Epitaxy (HWBE) using Ga and/or In metals, NH 3 gas or RF plasma nitrogen source. For both films, the surface morphology was smooth and the PL spectra showed strong near-band-edge emission without deep level emission. For the InGaN films, the highest In mole fraction of 24% was obtained with the substrate temperature ( T sub) of 575 and the RF power of 500 W, which was estimated from the shift of X-ray diffraction peak.

Growth of GaN and InGaN prepared by a hot wall beam epitaxy system with NH3

GaN and InGaN epilayers were successfully grown on the sapphire (0001) by hot wall beam epitaxy (HWBE) using Ga and In metals and NH3 gas. For the PL spectra of GaN epilayers, strong band edge (BE) emissions without deep level emissions were obtained. The In mole fraction of InGaN epilayers which were grown for the first time by HWBE was able to be controlled in the range less than 12% by changing only the substrate temperature (Tsub). Moreover, the growth interruption method was found to be effective for improving the crystalline quality of InGaN epilayers.

Wurtzite ZnxCd1 − xS layers grown by combining MBE and hot-wall beam epitaxy

ZnxCd1 − xS alloy layers revealing the wurtzite modification have been successfully grown by molecular beam epitaxy for the first time. The hexagonal crystal structure is achieved by using a wurtzite CdS buffer layer deposited by hot-wall beam epitaxy on a GaAs(1̄1̄1̄)B substrate. Characterization of the alloy films includes in situ RHEED investigations, X-ray diffraction and optical measurements. TEM diffraction patterns and reflection spectra are used to confirm the ZnxCd1 − xS alloys to be of the wurtzite type. Photoluminescence is dominated by localized exciton emission. For layers with high Zn content (x > 0.4), film quality decreases due to the increased mismatch to the CdS buffer and the fact, that the stable bulk phase for Zn-rich alloys is cubic.

Many-body effects and carrier dynamics in CdSe/CdS Stark superlattices.

Strained CdSe/CdS superlattices show very strong intrinsic piezoelectric fields due to the high piezoelectric constants in combination with a large lattice mismatch of 3.9%. The linear as well as the nonlinear optical properties are formed by these fields, which dominate the band structure. We report on the excitation-density-dependent luminescence and absorption of these superlattices grown by hot-wall beam epitaxy and compare the experimental results with a theory including both the electrostatic screening and the band-gap renormalization.

Growth of CdS Layers by Hot-Wall Beam Epitaxy and their Application as Quasi-Substrates for Molecular Beam Epitaxy of Wurtzite CdS<sub>1-x</sub>Se<sub>x</sub>

Growth of CdS Layers by Hot-Wall Beam Epitaxy and their Application as Quasi-Substrates for Molecular Beam Epitaxy of Wurtzite CdS<sub>1-x</sub>Se<sub>x</sub>

Epitaxial growth and photoluminescence of hexagonal CdS1−xSex alloy films

CdSSe ternary alloy films were grown on GaAs(111) by hot-wall beam epitaxy. The hexagonal crystal phase is obtained. The composition varies from 0 to 40% selenium. Luminescence spectroscopy at low temperatures shows a dominant effect by alloy disorder. Localization of carriers, for example, is still observed at a pulsed optical excitation density of 6 mJ/cm2. The overall quality of the CdSSe films is sufficient to use them as buffer layers for the growth of hexagonal superlattices.

Quality of ZnSe/GaAs epilayers studied by spatial correlation model of Raman scattering

In this letter, the spatial correlation model has been used for interpreting the line shapes of the first-order longitudinal-optical phonon Raman spectra of ZnSe/GaAs epitaxial layers. The good agreement between theoretical line shapes and the experiment measurements was illustrated for the samples grown by the molecular beam epitaxy (MBE), hot wall epitaxy (HWE), and hot wall beam epitaxy (HWBE).

HETEROEPITAXIAL GROWTH OF ZnSe ON GaAs(lOO) SUBSTRATE BY HOT WALL BEAM EPITAXY

ZnSe (100) single crystal films are grown by hot wall beam epitaxy on GaAs (100) substrate. The quality of films are examined by LEED and AES in situ. The films show sharp C(2×2) LEED pattern. When sample are prepared with high growth rate, the Raman spectra show that there are TO modes which are usually forbidden in ZnSe (100) films. ZnSe(100) films with twin can be explained by the TO modes in the Raman spectra. This interpretation is supported by the result of XRD.

Large Area (100)CdTe and CdZnTe Layers on (100)GaAs Grown by Hot Wall Beam Epitaxy for Hgcdte Photovoltaic MWIR-Detectorarray Application

ABSTRACTThe newly developed Hot Wall Beam Epitaxy was used for the growth of (100)CdTe and (100)Cd1-yZnyTe layers (y ∼ 0.04) on 1 inch (100)GaAs wafers. The structural properties of the epilayers were investigated by means of high resblution x-ray rocking curve measurements. The results demonstrate the high crystalline perfection of the layers. The CdTe and Cd1-yZnyTe/GaAs wafers were used as substrates for the growth of Hg1-xCdx Te by close space vapor phase epitaxy. The layers show excellent homogeneity. Across a 1 inch wafer the composition x varies by ±0.0026, and the width of the rocking curve (FWHM) by ±10arcsec. Values of the FWHM as low as 50arcsec for Hg1-xCdxTe (x = 0.32) on Cd1-yZnyTe/GaAs were obtained. Linear arrays of planar photovoltaic detectors were fabricated. Arrays of 32 elements show high uniformity of the cutoff wavelength and the responsivity. The variation of the cutoff wavelength is ±1.5% (±0.04μm) and the variation of the responsivity is ±3%.