Growth and characterization of strained superlattices delta-GaNxAs1-x/GaAs by molecular beam epitaxy

A series of superlattices delta-GaNxAs1-x/GaAs were grown by a DC plasma-N-2-assisted molecular beam epitaxy. The evolution of the surface reconstruction during the growth has been studied with the use of in situ reflection high-energy electron diffraction. The superlattices have been characterized by high-resolution X-ray diffraction measurements. Distinct satellite peaks indicate that the superlattices are of good quality. The N compositions in strained GaNxAs1-x monolayers are obtained from the dynamical simulations of the measured X-ray diffraction patterns. The periodicity fluctuations of N composition are obtained from a kinematical method dependent on the broadening of the satellite peaks of the X-ray diffraction. (C) 2000 Elsevier Science B.V. All rights reserved.

Investigation on quality of cubic GaN/GaAs(100) by double-crystal X-ray diffraction

Cubic GaN was grown on GaAs(100) by low pressure metal organic chemical vapor deposition (MOCVD). X-ray diffraction, scanning electron microscope (SEM) and photoluminescence (PL) spectra were performed to characterize the quality of the GaN film. The PL spectra of cubic GaN thin films being thicker than 1.5 mu m were reported. Triple-crystal diffraction to analyze orientation distributions and strain of the thin films was also demonstrated.

A study of the interface of CeO2/Si heterostructure grown by ion beam deposition

Epitaxial cerium dioxide films on single-crystal silicon substrates (CeO2/Si) have been grown by a dual mass-analyzed low-energy ion beam deposition (IBD) system. By double-crystal X-ray diffraction (XRD), Full Width at Half Maximum (FWHM) are 23' and 33' in the rocking curves for (222) and (111) faces of the CeO2 film, respectively, and the lattice-mismatch Delta a/a with the substrate is about - 0.123%. The results show that the CeO2/Si grown by IBD is of high crystalline quality. In this work, the CeO2/Si heterostructure were investigated by X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) measurements. Especially, XPS and AES depth profiling was used to analyze the compositions and structures in the interface regions of the as-grown and post-annealed CeO2/Si. It was found that there was no silicon oxide in the interface region of the as-grown sample but silicon oxide in the post-annealed sample. The reason for obtaining such high quality heterostructure mainly depends on the absence of silicon oxide in the surface at the beginning of the deposition. (C) 1998 Elsevier Science Ltd. All rights reserved.

Structural study of YSi1.7 layers formed by channeled ion beam synthesis

High quality YSi1.7 layers (chi(min) of Y is 3.5%) have been formed by 60 keV Y ion implantation in Si (111) substrates to a dose of 1.0 x 10(17)/cm(2) at 450 degrees C using channeled ion beam synthesis (CIBS). It shows that, compared to the conventional nonchanneled ion beam synthesis, CIBS is beneficial in forming YSi1.7 layers with better quality due to the lower defect density created in the implanted layer. Rutherford backscattering/channeling and x-ray diffraction have been used to study the structure and the strain of the YSi1.7 layers. The perpendicular and parallel elastic strains of the YSi1.7 epilayer are e(perpendicular to) = -0.67% +/- 0.02% and e(parallel to) = +1.04% +/- 0.08%. The phenomenon that a nearly zero mismatch of the YSi1.7/Si (111) system results in a nonpseudomorphic epilayer with a rather large parallel strain relative to the Si substrate (epsilon(parallel to) = +1.09%) is explained, and the model is further used to explain the elastic strain of epitaxial ErSi1.7 and GdSi1.7 rare-earth silicides. (C) 1998 American Vacuum Society.

GaN epilayers grown at high growth rate using gas source molecular beam epitaxy method

High-quality GaN epilayers have been grown by gas source molecular beam epitaxy using ammonia as the nitrogen source. During the growth, the growth rate is up to 1.2 mu m/h and can be varied from 0.3 to 1.2 mu m. The unintentional n-type doping as low as 7x10(17) cm(-3) was obtained at room temperature. Low-temperature photoluminescence spectrum was dominated by near-edge emission without deep-level related luminescence, indicative of high-quality epilayers. (C) 1998 Elsevier Science B.V. All rights reserved.

Properties of GaN epilayers with various growth conditions grown by gas source molecular beam epitaxy

GaN epilayers on sapphire (0001) substrates were grown by the gas source molecular beam epitaxy (GSMBE) method using ammonia (NH,) gas as the nitrogen source. Properties of gallium nitride (GaN) epilayers grown under various growth conditions were investigated. The growth rate is up to 0.6 mu m/h in our experiments. Cathodoluminescence, photoluminescence and Hall measurements were used to characterize the films. It was shown that the growth parameters have a significant influence on the GaN properties. The yellow luminescence was enhanced at higher growth temperature. And a blue emission which maybe related to defects or impurity was observed. Although the emission at 3.31 eV can be suppressed by a low-temperature buffer layer, a high-quality GaN epilayer can be obtained without the buffer layer. (C) 1998 Elsevier Science B.V. All rights reserved.

Influence of rapid thermal annealing on the optical properties of gallium nitride grown by gas-source molecular-beam epitaxy

Raman scattering, photoluminescence (PL), and nuclear reaction analysis (MA) have been employed to investigate the effects of rapid thermal annealing (RTA) on GaN films grown on sapphire (0001) substrates by gas-source molecular-beam epitaxy, The Raman spectra showed the presence of the E-2 (high) mode of GaN and shift of this mode from 572 to 568 cm(-1) caused by annealing. The results showed that RTA has a significant effect on the strain relaxation caused by the lattice and thermal expansion misfit between the GaN epilayer and the substrate. The PL peak exhibited a blueshift in its energy position and a decrease in the full width at half maximum after annealing, indicating an improvement in the optical quality of the film. Furthermore, a green luminescence appeared after annealing and increased in intensity with increasing annealing time. This effect was attributed to H concentration variation in the GaN film, which was measured by NRA. A high H concentration exists in as-grown GaN, which can neutralize the deep level, and the H-bonded complex dissociates during RTA, This leads to the appearance of a luminescent peak in the PL spectrum. (C) 1998 American Institute of Physics.

Molecular beam epitaxy growth of Iny2Al1-y2As/In0.73Ga0.27As/Iny1Al1-y1As/InP P-HEMTs with enhancement conductivity using an intentional nonlattice-matched buffer layer

Pseudomorphic Iny2Al1-y2As/In0.73Ga0.27As/Iny1Al1-y1As (y1 greater than or equal to 0.52) modulation-doped heterostructures with an intentional nonlattice-matched buffer layer were successfully grown by molecular beam epitaxy on (100)InP substrates. Fourier transform photoluminescence and double crystal x-ray diffraction measurements show a superior crystalline quality in the high In content channel, when In mole fraction increases from y1=0.52 to 0.55 in the Iny1Al1-y1As buffer layer. In this case, an increasing of 16.3% and 23.5% for conductivity (mu xn(s)) and mobility, related to the strain compensation in the In0.73Ga0.27As channel, was achieved, respectively, comparing to the structure containing a well-lattice matched buffer layer. With increasing the mismatch further (y1=0.58), a morphology with cross-hatched pattern was observed due to the onset of a large amount of misfit dislocations, and the electronic characterization is not able to be improved continuously. Because we can realize high quality strained P-HEMTs in a relative wide range of equivalent beam flux (EBF) ratios, the stringent control over the constant EBF is not indispensable on this In-based material system. (C) 1997 American Vacuum Society.

Molecular beam epitaxial growth of GaN on 3c-SiC/Si(111) substrates using a thick AIN buffer layer

Hexagonal GaN films (similar to 3 mu m) were grown on 3c-SiC/Si(111) and carbonized Si(111) substrates using a thick AlN buffer Cracks are observed on the surface of the GaN film grown on the carbonized Si(111), while no cracks are visible on the 3c-SiC/Si(111). XRD exhibits polycrystalline nature of the GaN film grown on the carbonized Si(111) due to poorer crystalline quality of this substrate. Raman spectra reveal that all GaN layers are under tensile stress, and the GaN layer grown on 3c-SiC/Si(111) shows a very low stress value of sigma(xx) = 0.65 Gpa. In low-temperature Photoluminescence spectra the remarkable donor-acceptor-pair recombination and yellow band can be attributed to the incorporation of Si impurities from the decomposition of SiC.

1.3 mu m high indium content (42.5%) GaInNAs/GaAs quantum wells grown by molecular beam epitaxy

High structural and optical quality 1.3 mu m GaInNAs/GaAs quantum well (QW) samples with 42.5% indium content were successfully grown by molecular beam epitaxy. The growth of well layers was monitored by reflection high-energy electron diffraction (RHEED). Room temperature photoluminescence (PL) peak intensity of the GaIn0.425NAs/GaAs (6 nm / 20 nm) 3QW is higher than, and the full width at half maximum (FWHM) is comparable to, that of In0.425GaAs/GaAs 3QW, indicating improved optical quality due to strain compensation effects by introducing N to the high indium content InGaAs epilayer. The measured (004) X-ray rocking curve shows clear satellite peaks and Pendellosung fringes, suggesting high film uniformity and smooth interfaces. The cross sectional TEM measurements further reveal that there are no structural defects in such high indium content QWs. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High Characteristic Temperature 1.3 mu m InAs/GaAs Quantum-Dot Lasers Grown by Molecular Beam Epitaxy

We report the molecular beam epitaxy growth of 1.3 mu m InAs/GaAs quantum-dot (QD) lasers with high characteristic temperature T-0. The active region of the lasers consists of five-layer InAs QDs with p-type modulation doping. Devices with a stripe width of 4 mu m and a cavity length of 1200 mu m are fabricated and tested in the pulsed regime under different temperatures. It is found that T-0 of the QD lasers is as high as 532K in the temperature range from 10 degrees C to 60 degrees C. In addition, the aging test for the lasers under continuous wave operation at 100 degrees C for 72 h shows almost no degradation, indicating the high crystal quality of the devices.

Optimization of VI/II pressure ratio in ZnTe growth on GaAs(001) by molecular beam epitaxy

ZnTe epilayers were grown on GaAs(0 0 1) substrates by molecular beam epitaxy (MBE) at different VI/II beam equivalent pressure (BEP) ratios (R-VI/II) in a wide range of 0.96-11 with constant Zn flux. Based on in situ reflection high-energy electron diffraction (RHEED) observation, two-dimensional (2D) growth mode can be formed by increasing the R-VI/II to 2.8. The Te/Zn pressure ratios lower than 4.0 correspond to Zn-rich growth state, while the ratios over 6.4 correspond to Te-rich one. The Zn sticking coefficient at various VI/II ratios are derived by the growth rate measurement. The ZnTe epilayer grown at a R-VI/II of 6.4 displays the narrowest full-width at half-maximum (FWHM) of double-crystal X-ray rocking curve (DCXRC) for (0 0 4) reflection. Atomic force microscopy (AFM) characterization shows that the grain size enlarges drastically with the R-VI/II. The surface root-mean-square (RMS) roughness decreases firstly, attains a minimum of 1.14 nm at a R-VI/II of 4.0 and then increases at higher ratios. It is suggested that the most suitable R-VI/II be controlled between 4.0 and 6.4 in order to grow high-quality ZnTe epitaxial thin films.

Molecular beam epitaxy of GaSb on GaAs substrates with AlSb/GaSb compound buffer layers

GaSb films with AlSb/GaSb compound buffer layers were grown by molecular beam epitaxy on GaAs (001) substrates. The crystal quality and optical properties were studied by high resolution transition electron microscopy and low temperature photoluminescence spectra (PL), respectively. It was found that the AlSb/GaSb compound buffer layers can restrict the dislocations into GaSb epilayers. The intensity of PL spectra of GaSb layer becomes large with the increasing the periods of AlSb/GaSb superlattices, indicating that the optical quality of GaSb films is improved.

REDUCTION OF CRYSTALLINE DISORDER IN MOLECULAR-BEAM EPITAXY GAAS ON SI BY MEV ION-IMPLANTATION AND SUBSEQUENT ANNEALING

Molecular beam epitaxy GaAs films on Si, with thicknesses ranging from 0.9-2.0-mu-m, were implanted with Si ions at 1.2-2.6 MeV to doses in the range 10(15)-10(16) cm-2. Subsequent rapid infrared thermal annealing was carried out at 850-degrees-C for 15 s in a flowing N2 atmosphere. Crystalline quality was analyzed by using Rutherfold backscattering/channeling technique and Raman scattering spectrometry. The experimental results show that the recrystallization process greatly depends on the dose and energy of implanted ions. Complete recrystallization with better crystalline quality can be obtained under proper implantation and subsequent annealing. In the improved layer the defect density was much lower than in the as-grown layer, especially near the interface.

IMPLANTATION ENERGY SELECTION IN MOLECULAR-BEAM EPITAXY GAAS FILMS ON SI SUBSTRATES

GaAs films made by molecular beam epitaxy with thicknesses ranging from 0.9 to 1.25-mu-m on Si have been implanted with Si ions at 1.2 MeV to dose of 1 x 10(15)/cm2. A rapid infrared thermal annealing and white light annealing were then used for recrystallization. Crystalline quality was analysed by using backscattering channeling technique with Li ion beam of 4.2 MeV. The experimental results show that energy selection is important for obtaining better and uniform recrystallized GaAs epilayers.