Ultraviolet light-driven epitaxial growth of gallium arsenide at reduced substrate temperatures

We report on the photodeposition of gallium arsenide on gallium arsenide and silicon at low substrate temperatures utilizing ultraviolet radiation. A 1000 W Hg-Xe arc lamp serves as the light source with triethylgallium and arsine serving as the reactants. In this study, single crystal gallium arsenide thin films are obtained at substrate temperatures of approximately 357°. The electrical, chemical and structural properties of the photodeposited films are presented and the mechanisms involved in the deposition process are discussed. It is found that both photolytic and pyrolytic mechanisms are involved in the deposition process for the experimental conditions considered and that the desorption of excess arsenic is important in the low temperature growth of GaAs using photochemical means.     

Self-Diffusion in gallium arsenide

The self-diffusion of arsenic in gallium arsenide has been studied over the temperature range 1000 to 1075δC using radiotracer techniques.⁷⁶As was diffused into GaAs samples at known arsenic pressures in sealed capsules. After diffusion, layers were removed from the surface using anodic oxidation followed by oxide dissolution. Diffusion profiles were obtained by measuring the⁷⁶As concentration in each sectioned layer by γ-radiation counting. Diffusion coefficients at P_{As 2} = 0.75 atm and over the temperature range 1000 to 1050δC were found to be 5.2 × 10^-16cm²s^-1 to 1.5 × 10^-15 cm²s^-1, leading to an activation energy of the order of 3.0^± 0.04 eV and a pre-exponential factor of 5.5 × l0^-4 ± 2.4 × 10^-4 cm²s^-1. Diffusion coefficients at P_{As 2} =3.0 atm were found to be 5.5 × 10^-15 and 9.8 × 10^-16 cm² s^-1 at 1050 and 1075δC, respectively. Results are discussed in terms of native point defect equilibria with the arsenic gaseous phase, and with respect to other work. It is deduced from our observed arsenic pressure dependence of the arsenic diffusivity that the most likely diffusion mechanism     

Selected-area GaAs epitaxial growth on Si free from detrimental sidewall interactions

The growth of GaAs on patterned Si trenches is essential for the realization of planarized monolithic co-integration of GaAs and Si devices. The patterned boundary regions also provide lateral sinks for stresses and defect propagation so long as the undesirable sidewall growth interactions are suppressed. In this study, we developed a cantilever patterning mask structure, with feature sizes ranging from 1.5 to 100 μm using overhung SiO₂ masks sitting on top of 3-μm-tall undercutting poly-Si patterns. The Si growth surface is protected and unetched. Patterned molecular beam epitaxial (MBE) grown GaAs layers are then prepared with complete elimination of sidewall interactions. Cross-sectional transmission electron microscopy (XTEM) results show there are reduced-defect areas in the regions 2 to 3 μm from the pattern edges compared to blanket grown areas. Combining the near-edge defect-reduction feature with other defect-reduction schemes incorporated during growth, patterned GaAs with sizes of 10 μm or under exhibits significant material quality improvements compared to blanket layer growth under the same conditions.     

Impurity redistribution during epitaxial growth

The distribution of impurities incorporated in epitaxial layers during their growth is determined by diffusion due to concentration gradients and by drift in the built-in electric field. This problem has been previously treated in the approximation that the impurities reach their equilibrium distribution during growth. We have extended this calculation to treat impurity drift and diffusion under non-equilibrium conditions, a situation much more characteristic of most realistic growth condi-tions. In the new calculation, the solution of the Shockley-Poisson problem is exact and the boundary con-dition at the growth interface is an approximation based on the electrostatics of surface states. The new calcu-lation also permits consideration of outdiffusion from the substrate, a phenomenon of technological significance. It is also capable of modeling variations of source im-purity concentration and growth rate during epitaxial growth. Calculations modeling n-type GaAs epitaxy of practical interest are presented. Supported by ONR Contract N00014-79-C-0840 and ONR Contract N00014-80-C-0762.     

Molecular beam epitaxial growth of carbon doped GaAs with elemental gallium and arsenic sources and a CCI4 gas source

CC1₄ has been used as a carbon acceptor dopant source for GaAs grown by elemental source molecular beam epitaxy. Deposition of CC1₄ during normal arsenic stabilized growth of GaAs resulted in low mobility, p-type material. Attempts to thermally crack the CC1₄ using a heated gas cracking source resulted in an even lower hole concentration and mobility. One possible explanation for this ineffective acceptor doping behavior, relative to growth environments containing hydrogen (metalorganic chemical vapor deposition) where CC1₄ is an effective dopant, is that hydrogen plays a role in the incorporation of the carbon. Another possible explanation for the poor doping behavior is that the CC1₄ was being modified by the gas cracker, even at relatively low gas cracker temperatures. Further experimentation with different injection schemes will be necessary to better understand the doping behavior. Depositing the CC1₄ onto static, gallium-rich surfaces produces GaAs:C with hole mobilities comparable to GaAs:Be. Average hole concentrations as high as 4 x 10¹⁹ have been demonstrated. Carbon doped AlGaAs/GaAs heterojunction bipolor transistors (HBT_s) have been fabricated with the same characteristics as Be doped HBTs grown in the same MBE system.     

Antisite arsenic incorporation in the low temperature MBE of gallium arsenide: Physics and modeling

A stochastic model for simulating the surface growth processes in the low temperature molecular beam epitaxy of gallium arsenide is developed to investigate the incorporation of antisite As and its dependence on the growth conditions including the dynamics of the physisorbed As on the surface. Three different kinetic models with a combination of surface kinetic processes such as incorporation of antisite As, evaporation of antisite As and incorporation of regular As. The kinetic model with all three surface processes was accepted as the best model due to its physical soundness and reasonableness of its model parameters. The arsenic flux, temperature, and growth rate dependences of antisite arsenic (As_Ga) obtained from our simulation are in excellent agreement with the experimental results. The activation energy of 1.16 eV and a frequency factor of 4×10¹²/s for the evaporation of antisite arsenic obtained from our model are in good agreement with experimental and theoretical estimates. At a constant substrate temperature and growth rate, the antisite arsenic concentration increases with arsenic flux for low fluxes and saturates beyond a critical flux. The critical arsenic flux increases with temperature and the saturation value of the As_Ga concentration decreases with temperature. As the arsenic flux increases, the coverage of the physisorbed layer increases and at a critical flux dictated by the fixed temperature and growth rate, the coverage saturates at its maximum value of unity (a complete monolayer) and hence the concentration of As_Ga saturates. Lower As_Ga concentration results at higher temperature due to more evaporation of As_Ga. Additionally, an analytical model is developed to predict the As_Ga concentration for various growth conditions.     

Atmospheric and low pressure metalorganic vapor phase epitaxial growth of vertical quantum wells and quantum well wires on submicron gratings

Nonplanar metalorganic vapor phase epitaxial growth on submicron gratings has been studied. Growth conditions have been determined to preserve the grating structure and also to enhance the formation of crescent shaped quantum well wire-like GaAs layers. These growth parameters have been used to grow the layer structure of a quantum well wire (QWW) laser, only needing one growth run. Although there is not yet clear evidence for two-dimensional quantum confinement, this technique offers some interesting perspectives for the realization of QWW lasers.     

Dose-rate effects in silicon-implanted gallium arsenide from low to high doses

For implantation of silicon dopant into gallium arsenide, sheet resistance and damage increase as the ion dose rate increases in the high-dose regime (>5.0 × 10¹³ cm⁻²). But, in the low-dose regime (<5.0 × 10¹² cm⁻²), although damage still increases with dose rate, the sheet resistance decreases. This qualitative difference implies that there must be a crossover point between the low- and high-dose regimes in the effect of damage and defect formation on dopant activation. This paper describes experiments in which damage and silicon dose were independently varied through the crossover point. Thermal wave, ion channeling, Hall effect measurements, and transmission electron microscopy were used to characterize structural and electrical changes that occur near the crossover. In GaAs implanted with silicon (²⁹Si⁺) at doses between 3 × 10¹² and 6 × 10¹³cm⁻², it is shown that electrical activation for low dose rates first begins to exceed that for high dose rates at a dose of 2 × 10¹³ cm⁻². Rapid growth of Type I dislocations also begins near this same dose, suggesting that there may be a link between defect formation and the crossover to negative dose-rate effects in the high-dose regime.     

Structural and electrical properties ofn-type bulk gallium arsenide grown from non-stoichiometric melts

The pulling of Si-doped GaAs from melts either Ga- or As-rich resulted in crystals having substantially different properties. The crystals grown from As-rich melts exhibited higher electron mobility with respect to those grown under Ga-rich conditions. These higher mobilities have been ascribed to more pronounced incorporation of silicon in donor sites and to lower density of acceptor-like complexes involving Si. The Ga-rich crystals were characterized by a lower concentration of dislocations. Such dislocation reduction is explained in terms of reduction of point defects (As interstitials) which can generate microloops and subsequently dislocations. An extensive TEM investigation further supports the idea of As_i as the point defect which more largely influences the structural properties of LEC GaAs. It is shown that the concentration and size of microdefects is drastically reduced when pulling from Ga-rich melts.     

利用热丝化学气相沉积制备外延生长多晶硅薄膜

Polycrystalline silicon(poly-Si) films were prepared by hot-wire chemical vapor deposition(HWCVD)at a low substrate temperature of 525 ℃. The influence of hydrogen on the epitaxial growth of ploy-Si films was investigated. Raman spectra show that the poly-Si films are fully crystallized at 525 ℃ with a different hydrogen dilution ratio(50%–91.7%). X-ray diffraction, grazing incidence X-ray diffraction and SEM images show that the poly-Si thin films present(100) preferred orientation on(100) c-Si substrate in the high hydrogen dilution condition.The P-type poly-Si film prepared with a hydrogen dilution ratio of 91.7% shows a hall mobility of 8.78 cm2/(V·s)with a carrier concentration of 1.3×1020 cm-3, which indicates that the epitaxial poly-Si film prepared by HWCVD has the possibility to be used in photovoltaic and TFT devices.     

X-Ray diffraction observation of surface damage in chemical-mechanical polished gallium arsenide

Two novel x-ray diffraction techniques with enhanced surface sensitivity, grazing incidence x-ray diffraction (GIXD) and inclined Bragg plane x-ray diffraction (IBXD), have been used to study surface damage in gallium arsenide (GaAs) due to bromine/methanol (Br₂/MeOH) chemical mechanical (CM) polishing. A factorial design was implemented to determine the effects of four polishing variables on the surface structure of GaAs. Precise lattice parameter measurements were made in both the surface regions using GIXD and deeper into subsurface regions using IBXD after the various CM polishing treatments. Bromine concentration was found to primarily affect the surface lattice parameter, while the total polish time influenced both the surface and subsurface lattice parameters in GaAs samples that were heavily damaged prior to CM polishing. The combined effect of polishing pad rotation speed and the force exerted on the sample was found to have a much greater effect on the surface lattice parameter than either variable had alone.     

Design of epitaxial Metal/AiAs/GaAs structures for enhancement of the schottky barrier height

Enhancement of the Schottky barrier height was obtained in MBE grown (CoAl or NiAl)/ AlAs/GaAs heterostructures by incorporating ultra thin AlAs layers between the metal and GaAs. By varying the AlAs thickness from 0 to 10 nm the effective barrier height, determined by current-voltage and capacitance-voltage measurements, could be tailored from 0.76 eV to 1.1 eV. Internal photoemission measurements were performed to verify the 1.1 eV barrier height. The temperature dependence of the current-voltage characteristics showed that thermionic emission was the dominant transport mechanism for all thicknesses of AlAs. The results were consistant with transport through the X-band of AlAs.     

Gas composition dependence of silicon nitride used as gallium diffusion barrier during GaAs molecular beam epitaxy growth on Si complementary metal oxide semiconductor

We have measured the effect of deposition parameters upon the utility of plasma enhanced chemical vapor depositon silicon nitride as a gallium diffusions barrier during molecular beam epitaxy growth of gallium arsenide on silicon submicron complementary metal oxide semiconductor electronics. It was found that the conditions under which the silicon nitride is deposited severely impact the ability of these films to be used as a diffusion barrier, with the most critical dependence upon the silane to nitrogen gas ratio.     

Effect of total pressure on the uniformity of epitaxial GaAs films grown in the Ga-HCl-AsH3-H2 system

The effect of total system pressure on the uniformity of epitaxial GaAs layers grown at 1023 K in the LP-VPE system has been studied with respect to layer thickness and dopant uptake. It was found that the uniformity of both of these quantities is distinctly improved when the hydrogen pressure is lowered from 3.3×10⁴ to 6.5×l0³ Pa. This behaviour is explained by the increase in gas phase diffusivity and the reduction in depletion of the gas phase during GaAs growth at reduced total pressure.     

脉冲激光沉积GaN薄膜的研究进展

脉冲激光沉积(PLD)技术凭借其低温生长优势,逐步在GaN薄膜外延领域得到广泛应用。回顾了近年来PLD技术外延生长GaN薄膜的研究进展,包括新型衬底上的GaN薄膜外延研究进展,以及作为克服异质外延的重要手段——缓冲层技术的发展现状。从目前的研究进展可以看出,应用PLD技术制备GaN薄膜及其光电器件具有广阔的发展前景。     

Growth condition dependence for GaAs selective epitaxial growth by molecular beam epitaxy

GaAs selective epitaxial growth by conventional molecular beam epitaxy (MBE) was studied while varying its growth conditions, such as substrate temperature. As pressure, growth rate, and Si or Be doping. Selectivity is improved with the increase in substrate temperature, and with the decrease in As pressure or growth rate. Si and Be were doped up to 3 x 10¹⁸ and 3 × 10¹⁹ cm⁻³, respectively. While no Si doping influence was observed, Be doping degraded the surface morphology. Selective epitaxial growth by conventional MBE with appropriate growth conditions will be applicable to device fabrication.     

Effect of MOVPE growth interruptions on the gallium arsenide interior interface morphology

We have studied MOVPE-grown interior GaAs/AlAs interfaces using highly selective etching combined with atomic force microscopy. We observe substantial restructuring for samples grown on both (100) exact and vicinal substrates. Interface structures differ significantly from sample surfaces after cool-down. On (100) exact substrates, the macroscopic monolayer island and terrace structure smoothes during growth interruptions over the whole 2 min period of time studied. A new, mesoscopic scale of roughness is detected for the first time. This structure does not depend on growth interruption time but does change its typical size at different growth temperatures. On vicinal substrates, we observe and quantify step bunching during growth interruption. The growing surface itself is smooth, in sharp contrast to the corresponding macrostepped GaAs sample surface obtained after cooling down.     

XeCl紫外激光与Xe红外激光同时振荡

Ｈｏ／Ｘｅ／Ｈｅ混合气体在横向快放电激发下同时输出ＸｅＣｌ紫外激光和Ｘｅ红外激光．研究了各参量对激光输出的影响，讨论了有关的动力学过程．     

Embedded epitaxial growth of 4H-SiC on trenched substrates and pn junction characteristics

Embedded epitaxial growth has been carried out on 4H-SiC substrates with very narrow and deep trenches. The growth behavior near trenches is investigated under various growth conditions. Epitaxial growth on the sidewalls and at the bottom of trenches was enhanced under a low C/Si ratio which may bring a larger surface diffusion length of reactant species. Pn diodes were fabricated by embedded epitaxial growth on trenched substrates. The crystallographic orientation of the trenches has been found to be important for device fabrication.     

Above 700 V superjunction MOSFETs fabricated by deep trench etching and epitaxial growth

Silicon superjunction power MOSFETs were fabricated with deep trench etching and epitaxial growth,based on the process platform of the Shanghai Hua Hong NEC Electronics Company Limited.The breakdown voltages of the fabricated superjunction MOSFETs are above 700 V and agree with the simulation.The dynamic characteristics,especially reverse diode characteristics,are equivalent or even superior to foreign counterparts.