Influence of reactant gas vapor pressure on the electrical properties and the electroluminescent efficiency of GaAs0.62P0.38

A number of workers have shown that the vapor pressure of the reactant gases strongly influences the electrical properties of GaAs vapor grown in the ASCI₃ system. This paper presents the results of a study of the effects of the variation of vapor pressures on GaAs_0.62P_0.38 grown in the hydride synthesis system. The material was analyzed using Hall effect measurements taken as a function of temperature from room to liquid helium temperatures, and using test electroluminescent diodes. A least squares fit was made to the Hall effect data using a model which includes the effects of two valley conduction to obtain densities of donors and acceptors and donor ionization energies. Increasing reactant gas pressure causes a decrease in donor and acceptor densities as N_D, N_A∞ P -2.5 which is slower than the P⁻⁴ observed by DiLorenzo in the ASCI₃ system. The ionization energy of the donors was quite high (100 meV) for the high and low pressures, and were less than 10 meV for the intermediate pressures. Hall mobilities at room and liquid nitrogen temperatures were best for material grown at intermediate pressures and the electroluminescent efficiencies of unencapsulated test diodes increased from 0.05 per cent at the extremes to above 0.1-0.2 per cent at the intermediate pressures. These variations are consistent with varying Si incorporation rate and varying density of point defects with varying reactant gas vapor pressure.     

Optimization of High-Quality AlN Epitaxially Grown on (0001) Sapphire by Metal-Organic Vapor-Phase Epitaxy

A systematic study is performed to optimize aluminum nitride (AlN) epilayers grown on (0001) sapphire by metal-organic vapor-phase epitaxy. Specifically, the impact of the AlN nucleation conditions on the crystalline quality and surface morphology of AlN epilayers is studied. Atomic force microscopy (AFM) and x-ray diffraction (XRD) results reveal that the nucleation layer plays a critical role in the growth of subsequent layers. The magnitude of the TMAl flow of AlN nucleation layer is found to have a strong effect on the crystalline quality and surface morphology of the high-temperature (HT) AlN epilayer. A simple Al adatom-diffusion-enhancement model is presented to explain the strong dependence of the crystalline quality and surface morphology on TMAl flow. Furthermore, ammonia flow, nucleation temperature, and growth time of the AlN nucleation layer are found to affect the surface morphology and the crystalline quality as well. A trade-off is found between surface morphology and crystalline quality; that is, we do not obtain the best surface morphology and the highest crystalline quality for the same growth parameters. For optimized AlN nucleation layers and HT AlN epilayers, a clear and continuously linear step-flow pattern with saw-tooth shaped terrace edges is found by AFM on AlN epilayers. Triple-axis x-ray rocking curves show a full-width at half-maximum (FWHM) of 11.5 arcsec and 14.5 arcsec for the (002) and (004) reflection, respectively. KOH etching reveals an etch-pit density (EPD) of 2 × 10⁷ cm⁻², as deduced from AFM measurements.     

Annealing studies of Be-implanted GaAs0.6P0.4

Differential resistivity and Hall effect measurements and secondary ion mass spectrometry (SIMS) are used to study the annealing behavior of Be-implanted GaAs_0.6P_0.4. Results similar to that previously reported for Be-implanted GaAs are observed, including outdiffusion of Be into the Si₃N₄ encapsulant during 900‡C annealing of high dose implants. Nearly all (85–100%) of the Be remaining after a 900‡C, 1/2 hr anneal is electrically active. However, the electrical activation at low annealing temperatures (600–700‡C) is much lower in GaAs_0.6P_0.4 than in GaAs. A substantial amount of diffusion is observed even for the low fluence Be implants in GaAs_0.6P_0.4 annealed at 900‡C, indicating a greater dependence of the diffusion on defect-related effects in the ternary. This work was supported by the Joint Services Electronics Program (U.S. Army, U.S. Navy, U.S. Air Force) under Contract DAAB-07-72-C-0259, by Monsanto Company, and by the Naval Electronic Systems Command. On leave at Cornell University, Department of Electrical Engineering, Ithaca, NY 14853.     

Use of tertiarybutylphosphine for the growth of InP and GaAs1-xPx

A newly-developed phosphorus source, tertiarybutylphosphine (TBP), which is much less toxic than PH₃, has been used to grow InP and GaAs_1-xP_x by atmospheric pressure organometallic vapor phase epitaxy (OMVPE). Excellent morphologies are obtained for the growth of InP between 560 and 630° C for TBP partial pressures larger than 0.5 x 10^-3. For the first time, V/III ratios as low as 3 have been used to grow InP epilayers with featureless morphologies at 600° C. To obtain good morphologies at both lower and higher temperatures, higher TBP partial pressures are necessary. The electron mobility increases and the electron density decreases as the temperature is increased. The highest room temperature mobilities and lowest electron densities, obtained at 630° C, are 3800 cm²/V-sec and 3 x 10¹⁵ cm^-3, respectively. The 10 K photoluminescence spectra of the InP epilayers at higher growth temperatures show no carbon contamination. Bound excition half widths as low as 3.0 meV have been measured. The use of TBP to replace PH₃ in the growth of GaAs_1-xP_x results in a nearly linear relationship between vapor and solid composition at 610° C,i.e., the P distribution coefficient is nearly unity. This contrasts sharply with the very low P distribution coefficient obtained using PH₃ at such low growth temperatures.     

凝胶固相反应法合成亚微米级钛酸锶钡陶瓷粉体

以TiO2和BaCO2,SrCO3粉体为原料,采用凝胶固相反应法合成了亚微米级Ba—Sr0.4TiO3陶瓷粉体。对凝胶固相反应过程进行了DSC热分析,并观察和测定了合成粉体的微观形貌、相结构和粒度分布。结果表明：Ba0.6Sr0.4TiO3粉体合成温度对应于857℃,在900～1000℃温度范围煅烧均可获得颗粒尺寸约0．5μm、粒径分布均匀的Ba0.6Sr0.6TiO3粉体。试验结果表明,凝胶固相合成Ba0.6Sr0.4TiO3的粉体粒径取决于原料粉体尺寸,经高温煅烧后因各组元元素的互扩散导致粉体粒径有所长大,要获得更细的合成粉体应采用更细的粉体原料。     

Growth of GaAs1−xPx/GaAs and InAsxP1−x/InP strained quantum wells for optoelectronic devices by gas-source molecular beam epitaxy

In this paper we show that pseudomorphically strained heterostructures of InAs _x P_1−x /InP may be an alternative to lattice-matched heterostructures of In_1−x Ga _x As _y P_1−y /InP for optoelectronic applications. We first studied the group-V composition control in the gas-source molecular beam epitaxy (GSMBE) of the GaAs_1-x P _x /GaAs system. Then we studied GSMBE of strained InAs _x P_1−x /InP multiple quantum wells with the ternary well layer in the composition range 0.15 <x < 0.75. Structural and optical properties were characterized by high-resolution x-ray rocking curves, transmission electron microscopy, absorption and low-temperature photoluminescence measurements. High-quality multiple-quantum-well structures were obtained even for highly strained (up to 2.5%) samples. The achievement of sharp excitonic absorptions at 1.06, 1.3 and 1.55μm at room temperature from InAs _x P_1−x /InP quantum wells suggests the possibility of long-wavelength optoelectronic applications.     

The preparation of modulation-doped GaAs/GaAs1-xPx strained-layer superlattices by metal organic chemical vapor deposition

Modulation-doped and uniformly doped GaAs/GaAs_1-xP_x strained-layer superlattices (SLS’s) have been prepared by metal organic chemical vapor deposition in a vertical, atmospheric pressure, quartz reaction chamber. The layers were doped with Se or Si by using a H₂Se or SiH₄ source and by using a vent-run valve-configuration to minimize dopant tailing. Carrier concentrations and mobilities were determined from Hall measurements at 300 and 77 K. The Se modulation-doped SLS’s with carrier concentrations in the range of 10¹⁶ to 10¹⁸ cm^-13 exhibited enhanced transport properties when compared to the properties of epitaxial GaAs prepared under the same conditions. The use of molecular sieves to purify the arsine or the use of SiH₄ resulted in lower mobilities for the SLS’s and the epitaxial GaAs layers. The presence of surface cracking or a large residual strain in the SLS’s also caused the modulation-doped SLS’s to have lower mobilities.     

La_(0.6)Sr_(0.4)CoO_3薄膜的制备及NTC特性研究

为研制具有较低室温电阻值的NTC薄膜热敏电阻,以La0.6Sr0.4CoO3陶瓷为靶材,采用RF磁控溅射法,在Al2O3基片上沉积了La0.6Sr0.4CoO3(LSCO)薄膜。研究了溅射过程中氩氧体积流量比对LSCO薄膜结晶性能和方阻的影响以及LSCO薄膜的阻温特性。结果表明:随着氩氧体积流量比的增加,LSCO薄膜的主晶相衍射峰强度及方阻均先增大后减小。LSCO薄膜具有显著的NTC特性,室温时的电阻温度系数α25为2.24×10–5;其lnR-T–1曲线具备良好的线形度,线性偏差仅为2.09%;另外,其室温时的电阻R25仅为18.75k?。     

Rapid consolidation of Ba0.6K0.4BiO3 into superconducting shapes

A rapid consolidation method is described for the superconducting compound Ba_0.6K_0.4BiO₃(BKBO). The starting material consists of phase pure BKBO powder that is cold pressed into the desired shape and sintered at 450°C in oxygen. A one step, quasi-isostatic consolidation is then used to densify the preform to approximately 90% theoretical density. The preform is oxygen annealed after consolidation. The resulting BKBO shape is phase pure and superconducting. This method is ideal for the production of superconducting shapes that can be used for sputtering and laser ablation targets.     

The preparation of CdSnP2/InP heterojunctions by liquid phase epitaxy from Sn-solution

Heterojunctions of n-type CdSnP₂ on p-type InP substrates are prepared by LPE from Sn-solutions. The significance of the tipping arrangement, of the initial solution composition and of the temperature program for preparing LPE layers of high quality is discussed. Heterodiodes cleaved from such LPE wafers electroluminesce under forward bias between 1 μm and 1.8 %m with internal quantum efficiencies approaching 1.8% at room temperature. When used as photovoltaic detectors, the quantum efficiency of these diodes surpasses that of Si for λ > 1.09 μ, and exceeds 1% for all wave-lengths between 0.96 and 1.3 μ.     

Investigation of GaAs]-x_x P crystals using the pseudo-kossel X-ray and photoluminescence techniques

Two indirect methods of determining composition in GaAs_{1-x x}P films grown epitaxially on GaAs substrates are discussed in this paper. In the first method precision lattice parameters, obtained using the pseudo-Kossel technique in back reflection, are compared to compositions determined with the electron microprobe. A plot of corrected lattice parameter vs. %GaP (microprobe) over the range of composition investigated (0.10 < x < 0.55) shows that Vegard’s law holds very closely in this system. The slope of the line is -0.002042 Å/%GaP while the intercept is within 0.028% of the established lattice parameter for GaAs. No point lies farther than 0.003 Å from the line describing Vegard’s law.     

Origin of photoluminescence from Er3+ centers in erbium doped GaAs and Al0.4Ga0.6 As grown by MBE

Sharp erbium-related intra-4f shell luminescence from Er doped GaAs and Al_0.4Ga_0.6 As epitaxial layers grown by molecular beam epitaxy (MBE) is presented. The emission arising from the two Er³⁺ excited states,⁴I_13/2 and⁴I_11/2 are studied. We have observed, by means of heat treatment under differentambients such as As, Ga and Al over pressure, that the optically active Er³⁺ preferentially occupies a Column III lattice site or Column III related defects. The photoluminescence results of co-doping Al_0.4Ga_0.6As:Er with Si and Be by MBE is also reported for the first time. A strong single 1.54 μm spontaneous emission line is achieved by co-doping with Be (≈1×10¹⁸ cm⁻³). This improvement is a result of successfully eliminating or suppressing the other transitions without sacrificing the 1.54 μm emission intensity or linewidth.     

The effect of trimethylaluminum concentration on the incorporation of P In AlxGa1−xPyAs1−y grown by organometallic vapor phase epitaxy

The organometallic vapor phase epitaxial (OM-VPE) growth of Al_xGa_1-xP_yAs_1-y on graded GaP_yAs_1-yGaAs in the compositional range 0 < x < 0.9 and 0 < y < 0.6 is reported. It is found that composition control can be easily achieved, and that the vapor phase ratio of trimethylaluminum to trimethylgallium strongly influences the incorporation of P in the solid. A model is developed which explains this in terms of competing reaction rates. The model gives a good fit to the experimental data.     

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.     

Vapor-grown In1−xGaxP electroluminescent junctions on GaAs

In_1?xGa_xP vapor-grown electroluminescent junctions have been deposited directly onto GaAs substrates. For these layers, an alloy composition within a few mole percent of the lattice-matching composition of 51.5 mole percent GaP has been found to be essential for high luminous efficiencies and for the avoidance of microcracks throughout the epitaxial layer. For In_1?xGa_xP alloys near this composition, the electroluminescence characteristics of the diodes have been found to be excellent, with room-temperature external quantum efficiencies as high as 0.2% attained for red emission near 6600 Å. The properties of In_.5Ga_.5P junction structures deposited directly onto GaAs ar? compared with those of In_1?xGa_xP layers previously prepared on GaP substrates.     

Alkoxide precursors for controlled oxygen incorporation during metalorganic vapor phase epitaxy GaAs and AlxGa1−xAs growth

Controlled oxygen incorporation in GaAs using Al-0 bonding based precursors, dimethyl aluminum methoxide (DMALO) and diethyl aluminum ethoxide (DEALO), is presented in this investigation. A comparison study of oxygen incorporation kinetics between nominally undoped Al_xGa_1−xAs using trimethyl aluminum and DMALO-doped GaAs suggests that DMALO is one of the most important oxygen-bearing agents responsible for unintentional oxygen incorporation in Al_xGa_1−xAs. Controlled oxygen doping using DEALO is reported for the first time. Oxygen incorporation behavior, especially on the effect of the V/III ratio, was found to be quite different from the case of DMALO, mainly due to the differences between methyl- and ethyl-based growth chemistries. Physical, electrical, and optical properties of these oxygen-doped GaAs are also reported.     

The growth and characterization of low resistivity n-type ZnSy Sel-y on (100) GaAs

ZnS_y Se_l°y epitaxial layers have been deposited on GaAs substrates by hydrogen transport from elemental sources and employing hydrides as the source of Group VI elements. The dependence of the sulphur mole-fraction, y, on substrate temperature and reactant partial pressures was investigated. Under Zn-rich conditions y increased almost linearly with the H₂S overpressure. Hall effect measurements indicated that the films were n-type with resistivity of 0.01 − 0.1Ω cm and high resolution electron microscopy indicated a sharp interface with low defect concentrations both at the interface and within the lattice-matched epitaxial layers.     

The CVD growth of Cu films using H2 as carrier gas

Copper chemical vapor deposition from Cu(hexafluoroacetylacetonate)trimethylvinylsilane (Cu(hfac)TMVS) was studied using a low pressure chemical vapor deposition system of a cold wall vertical reactor. The Cu films deposited using H₂ as a carrier gas revealed no impurities in the films within the detection limits of Auger electron spectroscopy and x-ray photoelectron spectroscopy. Using hydrogen as a carrier gas, the hydrogen not only acts as a reducing agent, but also reacts with the residual fragment of precursor. As a result, using H₂ as a carrier gas for Cu(hfac)TMVS resulted in Cu films of lower resistivity, denser microstructure and faster deposition rate than using Ar or N₂ as the carrier gas. Moreover, we found that N₂ plasma treatment on the substrate surface prior to Cu deposition increased the deposition rate of Cu films.     

Low temperature cleaning of Si by a H2/AsH3 plasma prior to heteroepitaxial growth of GaAs by metalorganic chemical vapor deposition (MOCVD)

A method using a H₂/AsH₃ plasma to clean the Si surface before GaAs heteroepitaxy was investigated and the dependence of the effectiveness of this treatment on arsine partial pressure was studied. Thin GaAs-on-Si films deposited on the plasma-cleaned Si were analyzed using plan-view TEM, HRXTEM and SIMS. Although not optimized, this method of Si cleaning makes heteroepitaxial deposition of GaAs possible. Some roughening of the Si surface was observed and a possible explanation is offered. Using the results of this study, thick (2.5–3.0μm) epitaxial GaAs films were then deposited and their quality was evaluated using RBS, XTEM and optical Nomarski observation. All Si surface cleaning and GaAs deposition were carried out at temperatures at or below 650°.