Polycrystalline GaAs Research Articles

Growth of ternary In xGa 1− xAs bulk crystals with a uniform composition through supply of GaAs

Ternary In 0.14Ga 0.86As bulk crystals with a uniform composition were found to be grown at a constant temperature by continuously supplying the depleted solute elements of Ga and As to the growth melt. The pseudo-binary InAs-GaAs melts were used as the growth melts. Compositionally graded 〈111B〉 In x Ga 1− x As (0.05 ≤ x ≤ 0.08) crystals were used as seed crystals. The liquid encapsulated Czochralski (LEC) technique with a method of supplying GaAs source material was used to grow the ternary bulk crystals. Polycrystalline GaAs was used as a source material. A 4 mm thick and uniform In 0.14Ga 0.86As single crystal was obtained.

In-situ selective-area epitaxy of GaAs using a GaAs oxide layer as a mask

Selective-area epitaxy of GaAs was performed by metalorganic molecular beam epitaxy using a GaAs oxide mask. No deposition of polycrystalline GaAs was observed on a GaAs oxide mask after the selective-area epitaxy using a trimethylgallium (TMG) and As 4 as source materials. An observation of the decomposition of TMG indicated that it occurred above 350°C on an oxide-free surface of GaAs, while decomposition did not occur below 550°C on a GaAs oxide surface. This surface-catalyzed decomposition of TMG explains the selectivity of GaAs growth.

Transport restriction effect for gaseous components on the carbon content of LEC GaAs

Gas convection above B 2O 3 was restricted using a quartz cap over the crucible to examine the gas transport effect on the carbon content of LEC GaAs crystals. It has been found that the carbon content of crystals grown with a cap closing the crucible is much larger than that of crystals grown without a cap. Also, a BN cylinder was introduced in a puller to reduce the interface area between GaAs melt and B 2O 3, and between B 2O 3 and the ambient gas. Estimates of carbon extraction rate from the melt were made by gas analysis in the puller which was operated in a hypothetical pulling process with different cylinder diameters. In addition, the dependence of the carbon concentration in polycrystalline GaAs remaining in the crucible on the pass time from the start of heating was investigated. The results suggest not only that the rate of carbon extraction is faster than incorporation, but also that the initial carbon content of the starting charge affects the carbon content of the grown crystal. It has been concluded that the extraction rate of carbon from the melt as well as the initial carbon content of the starting charge are significant factors in estimating the actual distribution of carbon concentration along the growth direction of LEC GaAs.

Optical reflectivity and amorphization of GaAs during decompression from megabar pressures

Polycrystalline GaAs was studied in a diamond anvil cell by optical reflection spectroscopy and energy-dispersive x-ray diffraction to pressures of 115 GPa (1.15 Mbar). Complete amorphization was observed at ambient conditions after decompression from 115 GPa, and, subsequent compression caused crystallization around 27 GPa to an orthorhombic phase. The results are compared with other group IV and III-V semiconductor materials and implantation-amorphized GaAs.

Photoluminescence studies of stress relief in selectively grown GaAs on Si by metalorganic chemical vapor deposition

The stress in GaAs grown selectively on Si by metalorganic chemical vapor deposition with two different nucleation techniques is studied by low temperature (4.2 K) photoluminescence. We demonstrate the effect of the SiO2 mask on the stress and show that the presence of polycrystalline GaAs on the SiO2 mask does not contribute significantly to the stress in the single crystals. Removal of the mask results in complete stress relief for features of size 10 × 10 μm2.

Hydrogen-passivated amorphous gallium arsenide thin films

Conditions have been developed for the deposition of stoichiometric thin films of amorphous gallium arsenide by the technique of flash evaporation. Structural properties of as-deposited and annealed thin films of a-GaAs have been studied using x-ray diffraction and transmission electron microscopy techniques. The as-deposited films are noncrystalline, structural ordering starts at about 200 °C, and the film becomes crystalline at about 400 °C with the structure matching with that of polycrystalline GaAs. The as-deposited a-GaAs thin films have been passivated using hydrogen plasma under different conditions. The influence of hydrogenation on these a-GaAs films has been studied using Fourier transform infrared absorption spectroscopy. These data are explained in terms of the various types of hydrogen bondings and the results are in excellent agreement with the earlier investigations on a-GaAs:H.

Detailed structural analysis of GaAs grown on patterned Si

The growth of GaAs on patterned Si substrates is essential for the integration of GaAs and Si devices. Moreover this growth may have to be done in wells to planarize the surfaces of the Si and GaAs devices for their interconnection. In this study, GaAs is grown by MBE on such patterned Si substrates, with window width down to 3 μm, and a complete structural characterization of the material is made by electron microscopy. In every case, SEM observations show a very good definition of the pattern by the contrast of the flat surface of the monocrystalline GaAs compared to the very rough surface of the polycrystalline GaAs. Cross-sectional observations by STEM or TEM on non-etched samples reveal that the quality of the monocrystalline GaAs is at least as good in terms of defect density as that of the standard GaAs on Si. On samples etched with a plasma to produce wells, grains often form against the Si sidewall. Chemical etching with lateral etching avoids contact of the growing GaAs with the Si sidewall and subsequent grain formation. The crystalline quality obtained on etched samples is not as good as on non etched samples. A way of preparing the wells to improve this crystalline quality is proposed.

Trimethylamine Gallane as a Precursor to Cubic Gallium Nitride and Gallium Arsenide. Metal Hydride Chemical Vapor Deposition

ABSTRACTCyclo-trigallazane, [H2GaNH2]3, is known to form bulk powders of the new cubic phase of gallium nitride upon pyrolysis. An explanation for this unusual example where the molecular structure of the precursor controls the crystal structure of the solid state product is presented. In a hot-wall atmospheric pressure chemical vapor deposition (CVD) reactor, arsine was found to react with TMAG to form films of polycrystalline GaAs which were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The growth rates for smooth films was 1-4 μm/h. In a low pressure CVD reactor, elemental arsenic vapor was also found to react with the TMAG to give GaAs thin films.

Passivation of defects in polycrystalline superlattices and quantum well structures

In order to broaden the available materials for superlattices and quantum well structures, well-passivated polycrystalline semiconductors and amorphous oxides such as pc-Si/a-SiO2, pc-Ge/a-GeO2 (pc: polycrystalline; a: amorphous) are proposed. Crucial in maintaining long scattering length involves the passivation of pc-Si (polycrystalline silicon) and pc-Ge. Specific means to passivate grain boundaries are discussed which consist of the use of the common dangling bond teminator, hydrogen, as well as amorphous oxides and other amorphous materials. This unique procedure may be extended to the entire group III-V semiconductors such as polycrystalline GaAs and InP.

The influence of grain boundaries on the performance efficiency of polycrystalline gallium arsenide solar cells

The effect of grain boundaries on the current-voltage characteristics of n + p polycrystalline GaAs solar cells has been studied in some detail. For the sake of convenience, a theoretical model that involves the solution of the continuity equation, and considers recombination at the grain boundary, grain boundary space-charge region, and the bulk of the semiconductors, has been used for the study. Calculated results for diffusion length, short-circuit current, open-circuit voltage, fill factor, and conversion efficiency have been compared with available experiments. Good agreement between the theory and the experiments attest to the validity of the model. The study indicates that grain size and doping levels are important device parameters for optimizing the solar cell properties.

A modified horizontal Bridgman technique without arsenic zone for growth of GaAs crystals

A modified two temperature zone horizontal Bridgman system without arsenic zone has been developed for the growth of GaAs single crystal. In this process, a short quartz ampoule, which was just long enough for sealing off the boat, was used. With a short quartz ampoule and a large charge of polycrystalline GaAs, the arsenic loss due to the dissociation of the melt was very small. The sticking between the boat and the crystal was eliminated; therefore, the crystal yield was greatly enhanced. The possible reasons for the elimination of the boat sticking and the stoichiometry control in this process are discussed. High quality Si-doped GaAs crystals with 2 inches in diameter and 30 cm in length have been routinely grown. The optoelectronic devices fabricated with these wafers showed better performance than commercial products.

Embedded growth of gallium arsenide in silicon recesses for a coplanar GaAs on Si technology

A GaAs on Si coplanar technology by molecular-beam epitaxy, that is suitable to combine GaAs and Si circuits on chip is reported. Coplanarity is obtained after the GaAs is grown embedded in masked wells in the Si substrate, which were formed by wet chemical etching with a controlled solution of HF:HNO3. Scanning electron microscope and profiling studies show the extreme flatness and the intentional misorientation of several degrees of the recessed surfaces. A possible process is proposed to realize a coplanar surface by lifting off polycrystalline GaAs with the masking dielectric. The GaAs surface step height remaining after liftoff is <0.6 μm for a 2-μm-thick deposit. Metallization without loss of continuity is performed over the GaAs to Si border with evaporated metal lines, 150 nm thick and 1.25 μm wide, indicating the feasibility of interconnecting side by side integrated devices in both semiconductor materials.

Effect of post-growth annealing on patterned GaAs on silicon

We have investigated the effect of post-growth thermal annealing on the defect surface of patterned GaAs on silicon. Significant improvements in defect structure of the patterned GaAs were observed by transmission electron microscopy (TEM) after short anneal times (15 min) at temperatures as low as 750 °C. At anneal temperatures of 950 °C, long-range single-crystal lateral regrowth of the original polycrystalline GaAs deposited over the amorphous patterning mask was observed. Micro-Raman spectroscopic characterization of the GaAs grown on the oxide/nitride mask corroborated the TEM results by showing a significant improvement in the crystalline quality of patterned GaAs on silicon following post-growth annealing.

Spatially selective photochemical vapor deposition of GaAs on synthetic fused silica

Photochemical vapor deposition of polycrystalline GaAs on synthetic fused silica is reported here. A Hg-Xe arc lamp is used as the light source with triethylgallium and arsine serving as the reactants. We report, for the first time, on a GaAs deposition process using the above-mentioned light source and reactants which is completely controlled by the light source with no deposition occurring in the absence of light. GaAs thin films of thicknesses up to 1.6 μm have been deposited. X-ray diffraction, energy-dispersive spectrometry, and optical transmittance are used to analyze these films.

Patterned growth of gallium arsenide on silicon

The molecular-beam epitaxial (MBE) growth of GaAs on silicon through openings in an oxide or nitride mask is an attractive alternative to the conventional full wafer deposition of GaAs on silicon for the monolithic integration of GaAs and Si devices. We have investigated techniques for the patterned growth of GaAs on Si and have found that single-crystal GaAs regions of high-crystalline quality can be successfully grown on silicon substrates. When the MBE growth is performed through holes in a mask onto the original planar silicon surface, the GaAs transformed from polycrystalline to single-crystal growth directly above the termination point of the wet etched oxide mask. Postgrowth annealing was found to drastically change the defect structure by causing single-crystal overgrowth of the mask, an elimination of the transition region defects, and significant grain growth in the remaining polycrystalline GaAs. Growth within etched trenches in the Si substrate also produced GaAs of good crystalline quality, although the defect density was higher than that observed in the GaAs grown on the original Si surface. Postgrowth annealing of the trench grown GaAs again led to a reduction in the number of structural defects and a dramatic change in defect morphology. Reasonable performance has been obtained from devices fabricated on both types of patterned GaAs.

MBE Growth of GaAs on an Exactly (001)-Oriented Si Substrate and Selective Epitaxial Growth for Fabrication of Modulation-Doped Fet's

ABSTRACTGaAs layers free of antiphase domains (APD's) have been grown by molecular beam epitaxy (MBE) on nominally (001)-oriented Si substrates. This is achieved by preheating the substrates at 950°C over 60 min or at 1000°C over 5 min in an ultrahigh vacuum. The maximum Hall mobility at 293 K is 5300 cm2/Vs for the APD-free GaAs layer doped with Si at a concentration of 2×1016 cm−3. Selective epitaxial growth of GaAs has been carried out on a Si substrate pattrened with SiO2, which was formed by wet O2 oxidation. By choosing an appropriate thickness of the SiO2 layer, thzxcSe warpage of wafers can be reduced to zero. While single-crystalline GaAs is grown on Si-exposed areas, highly-resistive (p ≧ 105 Ωcm) poly-crystalline GaAs is deposited on SiO2. This technique has been successfully applied for the device isolation of modulation-doped FET's (MODFET's, HEMT's, etc.) on Si without mesa-etching. The transconductance of the MODFET with a 3 μm-long gate reaches 88 mS/mm at 293 K.

MBE Growth of GaAs on an Exactly (001)-Oriented Si Substrate and Selective Epitaxial Growth for Fabrication of Modulation-Doped Fet's

AbstractGaAs layers free of antiphase domains (APD's) have been grown by molecular beam epitaxy (MBE) on nominally (001)-oriented Si substrates. This is achieved by preheating the substrates at 950 °C over 60 min or at 1000 °C over 5 min in an ultrahigh vacuum. The maximum Hall mobility at 293 K is 5300 cm2 /Vs for the APD-free GaAs layer doped with Si at a concentration of 2×1016 cm−3 . Selective epitaxial growth of GaAs has been carried out on a Si substrate pattrened with SiO2, which was formed by wet O2 oxidation. By choosing an appropriate thickness of the SiO2 layer, the warpage of wafers can be reduced to zero. While single-crystalline GaAs is grown on Si-exposed areas, highly-resistive (ρ ≧ 105 Ωcm) poly-crystalline GaAs is deposited on SiO2 . This technique has been successfully applied for the device isolation of modulation-doped FET's (MODFET's, HEMT's, etc.) on Si without mesa-etching. The transconductance of the MODFET with a 3 µm-long gate reaches 88 mS/mm at 293 K.

Organometallic Chemical Vapor Deposition of Gaas Using Novel Organometallic Precursors

ABSTRACTThe goals of the research are the design and synthesis of a new class of precursor compounds for III/V compound semiconductor materials, growth of films with these precursors and developoment of an understanding of the relationships between precursor structure, film growth reactions and film properties. Conventional OMCVD of III/V compound materials has a number of inherent safety and processing problems associated with the group III alkyl and group V hydride sources. Our approach to these problems is the synthesis of a single precursor with a fixed III:V stoichiometry and a direct two center, two electron sigma III V bond., These, compounds have the general formula,[R2M(R 2 E)] 2 and R2M(R 2 E) 2M R2 (MM = Al, Ga, In; E=P, As; R, R = alkyl, aryl). The III V bond in these compounds is stronger than the other bonds and the minium deposition temperature can be controlled by employing subsituents that undergo facile hydrocarbon elimination.A typical example is the use of [Me 2Ga(µ t Bu 2 As)] 2 as the single source for GaAs films. The organometallic precursor is a solid crystalline powder which is maintained at 130°C to generate enough vapor for OMCVD. Typical film growth conditions involve the use of H2 or He as the carrier gas, substrate temperatures of 500 to 700°C, and a total system pressure of 0.0002 Torr. GaAs(100), Si(100) (As doped 30 off toward (011) and quartz have been used as substrates. Film composition has been established with XPS. The Ga 3d, As 3d, and C ls signals at 18.8, 40.9, and 284.6 eV, respectively, reveal the films to be 1:1 Ga:As and void of carbon. The carbon levels are less than 1000 ppm. X ray diffraction and SEM results suggest polycrystalline GaAs on quartz and epitaxial GaAs on GaAs(100) and Si(100). (2 K) photoluminescence measurements on GaAs, grown on semi insulating GaAs(100) and Si doped GaAs(0 100) at 570 C. produce PL signals indicating that crystalline domains are present, the measurements indicate degeneratively n doped material and show that good Ga:As ratios and low levels (ca. 1 ppm) of impurities are present. Growth rates:∼ 1.0 mm/hour.

Photoluminescence characteristics of selectively grown GaAs and AlGaAs/GaAs quantum wells

GaAs and AlGaAs/GaAs multiple quantum wells (MQW) were selectively deposited on GaAs substrates patterned with native oxide, and photoluminescence (PL) characteristics of both the single crystal grown in open windows and the polycrystalline material deposited on the oxide masks were studied. Well-resolved distinct quantum-well (QW) transition peaks indicate no degradation of the epitaxial material quality in the small single-crystal areas. The PL of polycrystalline GaAs is very weak and the peak is centered around the near-band-edge transition energy of GaAs. Polycrystalline MQW structures exhibit much stronger PL signals, and the peak position shifts corresponding to the widths of the QWs grown. These results suggest that the quantum size effect is preserved in the polycrystalline material.

Low-pressure polishing of GaAs wafers

A low-pressure polishing procedure was developed where a GaAs wafer was immersed in a polishing solution of NaOCl and rotated with a speed of 6500 rpm. The strengths of the technique are illustrated by polishing non-lapped polycrystalline GaAs wafers, with final flatnesses better than 0.10 μm/cm.