Characterization and improvement of GaAs layers grown on Si using an ultrathin a-Si film as a buffer layer

GaAs epilayers grown on Si by metalorganic chemical vapor deposition (MOCVD) using an ultrathin a-Si buffer layer were characterized by deep-level transient spectroscopy (DLTS). Six electron traps with activation energies of 0.79, 0.67, 0.61, 0.55, 0.53 and 0.32 eV below the conduction band were determined by fitting the experimental spectra. Two of the levels, C (0.61 eV) and F (0.32 eV), were first detected in GaAs epilayers on Si and identified as the metastable defects M3 and M4, respectively. In order to improve the quality of GaAs/Si epilayers, another GaAs layer was grown on the GaAs/Si epilayers grown using MOCVD. The deep levels in this regrown GaAs epilayer were also studied using DLTS. Only the EL2 level was found in the regrown GaAs epilayers. These results show that the quality of the GaAs epilayer was greatly improved by applying this growth process.

Growth of GaAs on Si by using a thin Si film as buffer layer

We report a novel technique for growing high-quality GaAs on Si substrate. The process involves deposition of a thin amorphous Si film prior to the conventional two-step growth. The GaAs layers grown on Si by this technique using metalorganic chemical vapor deposition exhibit a better surface morphology and higher crystallinity as compared to the samples gown by conventional two-step method. The full width at half maximum (FWHM) of the x-ray (004) rocking curve for 2.2 mu m thick GaAs/Si epilayer grown by using this new method is 160arcsec. The FWHM of the photoluminescence spectrum main peak for this sample is 2.1 meV. These are among the best results reported so far. In addition, the mechanism of this new growth method was studied using high-resolution transmission electron microscopy.

PHOTOLUMINESCENCE SPECTRUM STUDY OF THE GAAS/SI EPILAYER GROWN BY USING A THIN AMORPHOUS SI FILM AS BUFFER LAYER

Recently, we reported successful growth of high-quality GaAs/Si epilayers by using a very thin amorphous Si film as buffer layer. In this paper, the impurity properties of this kind of GaAs/Si epilayers have been studied by using PL spectrum, SIMS and Hall measurement. Compared to a typical PL spectrum of the GaAs/Si epilayers grown by conventional two-step method, a new peak was observed in our PL spectrum at the energy of 1.462 eV, which is assigned to the band-to-silicon acceptor recombination. The SIMS analysis indicates that the silicon concentration in this kind of GaAs/Si epilayers is about 10(18) cm(-3). But its carrier concentration (about 4 x 10(17) cm(-3)) is lower than the silicon concentration. The lower carrier concentration in this kind of GaAs/Si epilayer can be interpreted both as the result of higher compensation and as the result of the formation of the donor-defect complex. We also found that the high-quality and low-Si-concentration GaAs/Si epilayers can be regrown by using this kind of GaAs/Si epilayer as substrate. The FWHM of the X-ray (004) rocking curve from this regrowth GaAs epilayer is 118 '', it is much less than that of the first growth GaAs epilayer (160 '') and other reports for the GaAs/Si epilayer grown by using conventional two-step method (similar to 200 '').

Low-frequency noise properties of GaN Schottky barriers deposited on intermediate temperature buffer layers

Metal-semiconductor-metal (MSM) structures were fabricated by RF-plasma-assisted MBE using different buffer layer structures. One type of buffer structure consists of an AlN high-temperature buffer layer (HTBL) and a GaN intermediate temperature buffer layer (ITBL), another buffer structure consists of just a single A IN HTBL. Systematic measurements in the flicker noise and deep level transient Fourier spectroscopy (DLTFS) measurements were used to characterize the defect properties in the films. Both the noise and DLTFS measurements indicate improved properties for devices fabricated with the use of ITBL and is attributed to the relaxation of residue strain in the epitaxial layer during growth process. (C) 2003 Elsevier Ltd. All rights reserved.

Influences of initial buffer layer deposition on electrical and optical properties in cubic GaN grown on GaAs(100) by metalorganic chemical vapor deposition

We present some results on the effect of initial buffer layer on the crystalline quality of Cubic GaN epitaxial layers grown on GaAs(100) substrates by metalorganic chemical vapor deposition. Photoluminescence and Hall measurements were performed to characterize the electrical and optical properties of cubic GaN. The crystalline quality subsequently grown high-temperature (HT) cubic GaN layers strongly depended on thermal effects during the temperature ramping process after low temperature (LT) growth of the buffer layers. Atomic force microscope (AFM) and reflection high-energy electron diffraction (RHEED) were employed to investigate this temperature ramping process. Furthermore, the role of thermal treatment during the temperature ramping process was identified. Using the optimum buffer layer, the full width at half maxim (FWHM) at room temperature photoluminescence 5.6 nm was achieved. To our knowledge, this is the best FWHM value for cubic GaN to date. The background carrier concentration was as low as 3 x 10(13) cm(-3). (C) 2000 Published by Elsevier Science S.A. All rights reserved.

The effects of carbonized buffer layer on the growth of SiC on Si

Carbonized buffer layers were formed with C2H4 on Si(100) and Si(111) substrates using different methods and SIC epilayers were grown on each buffer layer at 1050 degrees C with simultaneous supply of C2H4 and Si2H6. The structure of carbonized and epitaxy layers was analyzed with in situ RHEED. The buffer layers formed at 800 degrees C were polycrystalline on both Si(100) and Si(111) substrates whereas they were single crystals, with twins on Si(100) and without tu ins on Si(111)substrates. when formed with a gradual rise in substrate temperature from 300 degrees C to growth temperature. Raising the substrate temperature slowly results in the formation of more twins. Epilayers grown on carbonized polycrystalline lavers are polycrystalline. Single crystal epilayers without twins grow on single crystalline buffer layers without twins or with a few twins. (C) 1999 Elsevier Science B.V. All rights reserved.

The influence of thickness on properties of GaN buffer layer and heavily Si-doped GaN grown by metalorganic vapor-phase epitaxy

The physical properties of low-temperature-deposited GaN buffer layers with different thicknesses grown by metal-organic vapor-phase epitaxy have been studied. A tentative model for the optimum thickness of buffer layer has been proposed. Heavily Si-doped GaN layers have been grown using silane as the dopant. The electron concentration of Si-doped GaN reached 1.7 x 10(20) cm(-3) with mobility 30 cm(2)/V s at room temperature. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

The growth of ZnO on bcc-In2O3 buffer layers and the valence band offset determined by X-ray photoemission spectroscopy

This work was supported by the 863 High Technology R&D Program of China (Grant Nos. 2007AA03Z402 and 2007AA03Z451), the Special Funds for Major State Basic Research Project (973 program) of China (Grant No. 2006CB604907), and the National Science Foundation of China (Grant Nos. 60506002 and 60776015). The authors express their appreciation to Dr. Tieying Yang and Prof. Huanhua Wang (Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences) for XRD measurements and helpful discussions.

A 2-kW COIL with a square pipe-array JSOG and nitrogen buffer gas

A 2-kW-class chemical oxygen-iodine laser (COIL) using nitrogen buffer gas has been developed and tested since industrial applications of COIL devices will require the use of nitrogen as the buffer gas. The laser, with a gain length of 11.7 cm, is energized by a square pipe-array jet-type singlet oxygen generator (SPJSOG) and employs a nozzle bank with a designed Mach number of 2.5. The SPJSOG has advantages over the traditional plate-type JSOG in that it has less requirements on basic hydrogen peroxide (BHP) pump, and more important, it has much better operational stability. The SPJSOG without a cold trap and a gas-liquid separator could provide reliable operations for a total gas flow rate up to 450 mmol/s and with a low liquid driving pressure of around 0.7 atm or even lower. The nozzle bank was specially designed for a COIL using nitrogen as the buffer gas. The cavity was designed for a Mach number of 2.5, in order to provide a gas speed and static temperature in the cavity similar to that for a traditional COIL with helium buffer gas and a Mach 2 nozzle. An output power of 2.6 kW was obtained for a chlorine flow rate of 140 mmol/s, corresponding to a chemical efficiency of 20.4%. When the chlorine flow rate was reduced to 115 mmol/s, a higher chemical efficiency of 22.7% was attained. Measurements showed that the SPJSOG during normal operation could provide a singlet oxygen yield Y greater than or equal to 55%, a chlorine utilization U greater than or equal to 85%, and a relative water vapor concentration w = [H2O]/([O-2] + [Cl-2]) less than or equal to 0.1.

Investigation of some critical parameters of buffer conditions for the development of quantum dots-based optical sensors

The unique surface-sensitive properties make quantum dots (QDs) great potential in the development of sensors for various analytes. However, quantum dots are not only sensitive to a certain analyte, but also to the surrounding conditions. The controlled response to analyte may be the first step in the designing of functional quantum dots sensors. In this study, taking the quenching effect of benzoquinone (BQ) on CdTe QDs as model, several critical parameters of buffer solution conditions with potential effect on the sensors were investigated. The pH value and the concentration of sodium citrate in the buffer solution critically influenced the quenching effects of BQ.

Organic photovoltaic cell employing organic heterojunction as buffer layer

Hexadecafluorophthalocyaninatocopper (F16CuPc)/zine phthalocyanine (ZnPc) heterojunction layer has been used as buffer layer in organic photovoltaic (OPV) cells based on ZnPc and C-60. The F16CuPc/ZnPc heterojunction with highly conductive property decreased the contact resistance between the indium-tin-oxide anode and the organic layer. As a result, the short-circuit current density and fill factor were increased, and the power-conversion efficiency was improved by over 60%. Therefore, the method provides an effective path to improve the performance of OPV cells.

Effects of thermal annealing on polymer photovoltaic cells with buffer layers and in situ formation of interfacial layer for enhancing power conversion efficiency

We have investigated the effects of thermal annealing before and after cathode deposition on poly(3-hexylthiophene)(P3HT)/[6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend photovoltaic cells with different cathode buffer layers. The introduction of cathode buffer layer such as lithium fluoride (LiF) and calcium oxide (CaO) in pre-annealing cells can increase the open-circuit voltage (V-oc) and the power conversion efficiency (PCE). Post thermal annealing after cathode deposition further enhanced the PCE of the cells with LiF/Al cathode.

Enhanced charge collection in polymer photovoltaic cells by using an ethanol-soluble conjugated polyfluorene as cathode buffer layer

We report enhanced polymer photovoltaic (PV) cells by utilizing ethanol-soluble conjugated poly (9, 9-bis (6'-diethoxylphosphorylhexyl) fluorene) (PF-EP) as a buffer layer between the active layer consisting of poly(3-hexylthiophene)/[6, 6]-phenyl C61-butyric acid methyl ester blend and the Al cathode. Compared to the control PV cell with Al cathode, the introduction of PF-EP effectively increases the shunt resistance and improves the photo-generated charge collection since the slightly thicker semi-conducting PF-EP layer may restrain the penetration of Al atoms into the active layer that may result in increased leakage current and quench photo-generated excitons. The power conversion efficiency is increased ca. 8% compared to the post-annealed cell with Al cathode.