One-sidewall-seeded epitaxial lateral overgrowth of a-plane GaN by metalorganic vapor-phase epitaxy

The selective regrowth of GaN during sidewall-seeded epitaxial lateral overgrowth was performed. In addition to adjusting the V/III ratio, control of offset angle of the sidewall was found to be effective for realizing one-sidewall-seeded a-plane (1 1 2¯ 0) GaN on r-plane (1 1¯ 0 2) sapphire. The number of coalescence regions on the grooves was reduced, and threading-dislocation and stacking-fault densities as low as 10⁶–10⁷ cm⁻² and 10³–10⁴ cm⁻¹, respectively, were successfully realized.     

Stability of GaAs oxide under metalorganic molecular beam epitaxy process

Well-defined oxide of GaAs can be used as a mask material for selective-area metalorganic molecular beam epitaxy (MOMBE) of GaAs. In this study, the reaction between triethylgallium (TEG) and the GaAs oxide layer was studied using a quadrupole mass spectrometer (QMS) and an atomic force microscope (AFM). Results of the QMS observation showed that TEG was reflected on the GaAs oxide surface until the start of desorption of the GaAs oxide, and the GaAs oxide layer was desorbed from the wafer after a large time delay from the start of TEG supply. AFM images showed that many holes appeared on the GaAs oxide surface during the desorption of the GaAs oxide. The effect of incident TEG upon the stability of the GaAs oxide mask is discussed.     

Kinetics of dopant incorporation in GaAs grown by organometallic vapor-phase epitaxy

A diffusive capture reaction of dopant atoms by relevant host atoms, via the Rideal–Eley mechanism, in GaAs grown by organometallic vapor-phase epitaxy is shown to result in the dopant concentration in the crystal acquiring a dependence on p_Ga (which is proportional to the growth rate) in agreement with data on S_As, Zn_Ga, and Si_Ga where p_Ga is the partial pressure of trimethylgallium in the input gas stream.     

Difference of anisotropic structures of InAs/GaAs quantum dots between organometallic vapor-phase epitaxy and molecular beam epitaxy

The anisotropies of the baseline in and [1 1 0] of InAs quantum dots (QDs) fabricated by molecular beam epitaxy (MBE) and organometallic vapor-phase epitaxy (OMVPE) are investigated. The structural and optical difference between QDs by MBE and OMVPE are investigated through an atomic force microscopy, a transmission electron microscopy, and a photoluminescence polarization measurement. It is found that the InAs QD structural anisotropy in MBE agrees with the individual growth rate anisotropy. Moreover, it is found that the mixture of the different structural anisotropies is unique in OMVPE at low growth temperature (440°C) and the growth mode is complex. From the photoluminescence polarization measurement, the InAs QD structures which mainly contribute to the optical property are decided by the plus and minus of the polarization degree of the ground state, and it is shown that the baseline anisotropy of the QDs mainly agrees with the growth rate anisotropy.     

Fabrication of GaAs quantum wires by metalorganic molecular beam epitaxy and their optical properties

We have grown GaAs quantum wires having nominal cross-sectional dimensions of 20×20 nm² buried in AlGaAs layers, by lateral metalorganic molecular beam epitaxy on the terraced sidewalls of mesa-grooved ( ) substrates. In the photoluminescence spectrum of this sample at 77 K, a dominant emission has been observed at a peak wavelength of 780 nm which corresponds to a blue shift of 80 meV from the GaAs bulk transition. Emission spectroscopy from different positions and imaging by cathodoluminescence have demonstrated that this emission was generated from the sidewalls, indicating that it originates from the quantum wire.     

Dependence of impurity incorporation upon substrate misorientation during GaAs growth by metalorganic vapour phase epitaxy

Doping studies of the incorporation behaviour of three different dopants (Zn, In and Si) versus the misorientation of the (100) surface during MOVPE growth of GaAs have been carried out with diethylzinc, trimethylindium and disilane as precursors. The incorporation of the dopants has been studied as function of the input mole fraction dopant, growth temperature, degree and direction of misorientation. In order to explain the results we discuss the BCF theory and the nature of the steps as function of above mentioned parameters. It appears that the BCF theory alone cannot explain the results, a counteracting mechanism has been introduced based on preferential arsenic desorption from the step edges.     

Growth of ZnTe layers on (111) GaAs substrates by metalorganic vapor phase epitaxy

ZnTe layers were grown on (111) GaAs substrates by metalorganic vapor phase epitaxy using dimethylzinc and diethyltelluride as the source materials. X-ray diffraction analysis revealed that epitaxial ZnTe layers can be obtained on (111) GaAs substrates. X-ray rocking curves, Raman spectroscopy, and photoluminescence measurements showed that the crystal quality of ZnTe layers depends on the substrate temperature during the growth. A high-crystalline quality (111) ZnTe heteroepitaxial layer with strong near-band-edge emission at 550 nm was obtained at a substrate temperature of 440 °C.     

Platinum-catalyst-assisted metalorganic vapor phase epitaxy of InN

This paper reports the first attempt of the Pt-catalyst-assisted MOVPE growth of InN. In order to enhance NH₃ decomposition at a relatively low growth temperature (～550 °C), Pt is used as a catalyst. The catalyst is installed in the NH₃ introduction tube in the MOVPE reactor and the tube is located just above the susceptor to be heated. Compared with InN films grown without the catalyst, the samples grown with Pt catalyst show improved electrical properties; a carrier concentration in the order of 10¹⁸ cm^?3 and a Hall mobility as high as 1350 cm²/Vs are obtained. The crystalline quality is also improved by employing the catalyst and a tilt fluctuation as low as 8.6 arcmin is obtained for a sample grown on a GaN/sapphire template. It is confirmed that for InN films grown at 550 °C with Pt catalyst, the electrical and crystallographic properties are also improved with increase in thickness. These results indicate that the growth at around 550 °C with the Pt catalyst is performed under the circumstances where NH₃ is effectively decomposed, whereas the deterioration of InN during growth is significantly suppressed.     

Effects of ultraviolet irradiation during growth of ZnSe epilayers by atmospheric pressure metalorganic vapor-phase epitaxy using dimethyl zinc and H2Se

This work has investigated the effects of ultraviolet irradiation on the epitaxial growth process of undoped ZnSe by atmospheric-pressure metalorganic vapor phase epitaxy. Dimethyl zinc and H₂Se at a [VI]/[II] mole ratio of 20 were the source gases used for growth onto (100)-just oriented semi-insulating GaAs substrates. Hydrogen was used as the carrier gas. A 500 W Hg-Xe lamp irradiated the substrate at 300 nm wavelength during growth. Growth temperature was varied from 210 to 450°C. Epilayers grown in the presence of irradiation experienced a prominent decrease in growth rate, which occurred even at high temperatures. Through a combination of surface and vapor-phase reactions, UV irradiation also affected the photoluminescence properties, crystalline quality, and surface morphology of the epilayers.     

Surface diffusion length of Ga adatoms in molecular-beam epitaxy on GaAs(100)-(110) facet structures

By the molecular-beam epitaxial (MBE) growth of GaAs on [001]-mesa stripes patterned on GaAs(100) substrates, (110) facets were formed on the mesa edges defining (100)-(110) facet structures. The surface diffusion length of Ga adatoms along the [010] direction on the mesa stripes was obtained for a variety of growth conditions by in-situ scanning microprobe reflection high-energy electron diffraction (μ-RHEED). Using these values and the corresponding growth rate on the GaAs(110) facets, the diffusion length on the (110) plane was estimated. We found that the Ga diffusion length on the (110) plane is longer than that on the (100) and (111)B planes. The long diffusion length on the (110) plane is discussed in terms of the particular surface reconstruction on this plane.     

GaN/GaAs(1 0 0) superlattices grown by metalorganic vapor phase epitaxy using dimethylhydrazine precursor

Superlattices of cubic gallium nitride (GaN) and gallium arsenide (GaAs) were grown on GaAs(1 0 0) substrates using metalorganic vapor phase epitaxy (MOVPE) with dimethylhydrazine (DMHy) as nitrogen source. Structures grown at low temperatures with varying layer thicknesses were characterized using high resolution X-ray diffraction and atomic force microscopy. Several growth modes of GaAs on GaN were observed: step-edge, layer-by-layer 2D, and 3D island growth. A two-temperature growth process was found to yield good crystal quality and atomically flat surfaces. The results suggest that MOVPE-grown thin GaN layers may be applicable to novel GaAs heterostructure devices.     

p-Type GaAs doped by diiodomethane (CI2H2) in molecular beam epitaxy, metalorganic molecular beam epitaxy, and chemical beam epitaxy

Highly p-type carbon-doped GaAs epitaxial layers were obtained using diiodomethane (CI₂H₂) as a carbon source. In the low 10¹⁹ cm⁻³ range, almost all carbon atoms are electrically activated and at 9×10¹⁹ cm⁻³, 91% are activated. The carbon incorporation efficiency in GaAs layers grown by metalorganic molecular beam epitaxy (MBE) and chemical beam epitaxy (CBE) is lower than that by MBE due to the site-blocking effect of the triethylgallium molecules. In addition, in CBE of GaAs using tris-dimethylaminoarsenic (TDMAAs), the carbon incorporation is further reduced, but it can be increased by cracking TDMAAs. Annealing studies indicate no hydrogenation effect.     

Effect of arsenic species on the kinetics of GaAs nanowires growth by molecular beam epitaxy

GaAs nanowires (NWs) are grown on GaAs (1 1 1) B substrates in a molecular beam epitaxy system, by Au-assisted vapor–liquid–solid growth. We compare the characteristics of NWs elaborated with As₂ or As₄ molecules. In a wide range of growth temperatures, As₄ leads to growth rates twice faster than As₂. The shape of the NWs also depends on the arsenic species: with As₄, regular rods can be obtained, while pencil-like shape results from growth with As₂. From the analysis of the incoming fluxes, which contributes to the NWs formation, we conclude that the diffusion length of Ga adatoms along the NW sidewalls is smaller under As₂ flux as compared to that under As₄ flux. It follows that As₂ flux is favourable to the formation of radial heterostructures, whereas As₄ flux is preferable to maintain pure axial growth.     

Metalorganic vapor-phase epitaxy of III/V phosphides with tertiarybutylphosphine and tertiarybutylarsine

Indium phosphide, gallium arsenide phosphide, and aluminum indium phosphide have been deposited by metalorganic vapor-phase epitaxy using tertiarybutylphosphine and tertiarybutylarsine. The effects of growth temperature and V/III ratio on the amount of silicon, sulfur, carbon, and oxygen in InP have been determined. Minimum incorporation was observed at 565 °C and a V/III ratio of 32. In this case, the material contained a background carrier concentration of 2.7×10¹⁴ cm⁻³, and the Hall mobilities were 4970 and 135,000 cm²/V s at 300 and 77 K. The oxygen contamination in AlInP was found to be only 9.0×10¹⁵ cm⁻³ for deposition at 650 °C and a V/III ratio of 35. The relative distribution of arsenic to phosphorus in GaAs_yP_1−y was determined at temperatures between 525 and 575 °C. The distribution coefficient [(N_As/N_P)_film/(P_TBAs/P_TBP)_gas] ranged from 25.4 to 8.4, and exhibited an Arrhenius relationship with an apparent activation energy of 1.2 eV.     

AlInP benchmarks for growth of AlGaInP compounds by organometallic vapor-phase epitaxy

We have demonstrated that source material and growth system purity can be successfully evaluated by characterizing AlInP samples grown by organometallic vapor-phase epitaxy with photocurrent versus voltage measurements in an electrochemical cell. The samples can be grown and characterized in about 1 h, making them well-suited for system benchmarks. Zn-doped AlInP has the greatest sensitivity for O contamination, a recurring problem in the growth of AlGaInP alloys. High O concentrations in the Zn-doped benchmarks cause the photoresponse to fall dramatically. Secondary ion mass spectrometry data are consistent with compensation of Zn acceptor states by O donor-like trap states. Photocurrents of Si-doped and Se-doped AlInP are less sensitive to the O contamination, and the behavior of these n-type samples suggests that multiple energy states can be associated with the O impurities and dopant atoms. The benchmarks have been used to identify O contamination in trimethyl indium and phosphine and to evaluate new growth systems. Application of the benchmark to growth of GaInP solar cells with AlInP window layers is also discussed.     

On the kinetics of GaAs chemical transport and epitaxy in the system GaAs–I2

Kinetic analysis of experimental data on transport and epitaxial growth of GaAs with iodine in closed and in open tube systems has been carried out. The uniformly shrinking core model has been applied to study GaAs transport kinetics in the closed system. The kinetics of GaAs epitaxy in the open one is interpreted according to a model which assumes that in the initial stage of chemical reactions new phase nuclei are formed instantly at a constant number of active centers and that the nuclei grow isotropically.     

MOVPE生长AlAs/GaAs Bragg反射膜

采用常压金属有机物气相沉积法生长AlAs/GaAs周期性反射膜,并利用双晶X射线衍射、扫描电子显微镜和记录式分光光度计等分析手段,对材料结构及光学性质进行了分析.实验结果表明,在780℃连续生长的薄膜结构和晶体质量都很好,但是反射率低;通过模拟计算,连续生长存在渐变层,而渐变层大大降低了反射率;在同样生长条件下间断生长得到较高反射率的薄膜材料.     

Improvements in silicon doping of InP and GaInAs in metalorganic molecular beam epitaxy

We have investigated the Si doping of InP and GaInAs in metalorganic molecular beam epitaxy (MOMBE) by using a conventional Si effusion cell. In order to reduce the formation of SiC promoted by the background gases in MOMBE, we introduced a liquid nitrogen cooled baffle between the cell and the mechanical shutter. The results show that the passivating reaction can be substantially suppressed by a proper treatment of the source cell. The doping efficiency remains constant over a long period of operation corresponding to a large total layer thickness (>100 μm). The comparison of SIMS analysis with Hall data reveals an electrical activation of Si in InP up to 100% and about 65% for Si in GaInAs. These results and the investigations on doping profiles show that Si is a suitable donor in InP and GaInAs in the MOMBE process.     

Thermal decomposition of di-tertiarybutyl selenide and dimethylzinc in a metalorganic vapour phase epitaxy reactor

The thermal decomposition of di-tertiarybutyl selenide (DtBSe), both alone and in the presence of dimethylzinc (DMZn), was investigated using “ex-situ” Fourier transform infrared (FTIR) absorption spectroscopy in a low-pressure metalorganic vapour phase epitaxy (LP-MOVPE) reactor. The decomposition of DtBSe alone, yields isobutene as the major product, with a much smaller proportion of isobutane detected. Pyrolysis of DMZn in dihydrogen in the presence of DtBSe is very similar to pyrolysis of DMZn alone in dihydrogen with methane the exclusive product. This indicates that co-pyrolysis of the DMZn/DtBSe mixture occurs via radical attack by H on DMZn and largely independent pyrolysis of DtBSe via a β-hydrogen elimination reaction. Traces of the intermediate tertiarybutyl selenol (^tBuSeH) were also detected. The small difference observed in the decomposition behaviour of the DtBSe-DMZn mixture in a dihydrogen compared to a helium ambient further indicate that the pyrolysis processes are independent. These conclusions are supported by PM3 semi-empirical molecular orbital calculations, which indicate that the most likely pathway for unimolecular dissociation of DtBSe is via β-hydrogen elimination with C---Se bond homolysis only likely to be an effective competing mechanism at higher growth temperatures and reactor pressures.     

Deep hole trap level of nitrogen-doped ZnSe grown by metalorganic vapor phase epitaxy

We investigated the hole trap level of nitrogen-doped ZnSe grown by a metalorganic vapor phase epitaxy method. The deep level transient spectroscopy (DLTS) signal and the C-V profile were measured to obtain the trap level, the capture cross section and the trap concentration. A deep hole trap level of about 1 eV from a valence band (labeled TLIS) was extracted from the tail of the DLTS peak. The distributions of the capture cross section and the trap level of the samples for different growth conditions were drawn in a figure to investigate the validity of the resolution of the DLTS signal. The origin of TLIS is thought to be in relation to the ionized acceptor or the charged acceptor-like localized defects.