"In Situ Etching of GaAs, AlAs, and InAs in Solid Source MBE with Elemental Iodine:" M. MICOVIC, D.L. Miller, Electronic Materials and Processing Research Laboratory, Department of Electrical Engineering, The Pennsylvania State University, University Park, PA 16802
In situ etching of GaAs, AlAs, and InAs with elemental iodine in solid source Molecular Beam Epitaxy (MBE) has been investigated. Etch rates were estimated using Reflection High Electron Diffraction (RHEED) oscillations. No changes of the surface reconstruction on GaAs and AlAs have been observed under iodine flux. A series of doped and undoped GaAs, and AlGaAs samples for evaluation of the material quality was grown under iodine flow rate which corresponds to an etch rate of 0.1 monolayers per second. The RHEED patterns of these structures were strong and streaky indicating very smooth two dimensional growth. The room temperature photoluminescence (PL) intensity under HeNe laser light excitation (25 W/cm2 light power density) of a GaAs structure grown with the iodine was more than 20 times stronger than the PL intensity of the same structure grown without iodine. The 4.2 K PL spectrum of the two samples was similar. These preliminary results suggest that the iodine has a potential application in the growth of semiconductor laser structures.
"Etching Mechanisms of GaAs and AlAs using CBr4 in MOCVD Growth:" KOUTA TATENO, Yoshitaka Kohama, NTT Optoelectronics Laboratories, 3-1 Morinosato-Wakamiya, Atsugi-shi, Kanagawa 243-01, Japan
Carbon (C) is a very attractive p-type dopant for AlGaAs and has been used for HBTs, VCSELs and so on. Using CBr4 as a C source, the C concentration can be reproducibly varied over a wide doping range. However, it is known that CBr4 brings about a problem of growth rate reduction when the C doping is high. We report on the CBr4 etching mechanisms of GaAs and AlAs in MOCVD growth.
The growth was conducted in a horizontal MOCVD reactor at 76 Torr. TMGa, TMAl and AsH were used as the sources. Three samples were grown, each comprised a stack of alternate 1000Å (nominal) AlAs and GaAs layers. For each sample one parameter, either growth temperature (Tg), V/III ratio or CBr4 flow rate was varied between each period of the stack. Their cross sections were observed by SEM.
The growth reduction rate ([[gamma]]=(lnon - lCBr4)/lnon) increases in both GaAs and AlAs as a function of the CBr4 flow. Here, lCBr4 and lnon denote the thickness of the CBr4-doped and non-doped layers respectively. However, the results were different in the two materials: namely, [[gamma]] in GaAs is 4 times larger than in ALAs at a V/III of 60 and Tg of 650deg.C; in GaAs [[gamma]] is proportional to [AsH3]-0.5 while in ALAs to [AsH3]-1, and the activation energies of [[gamma]] in GaAs and AlAs are 1.2 eV and -1.5 eV respectively. For GaAs, the etching appeared to be conducted by HBr produced from the CBr4, since our results were similar to those obtained using CCl4 (activation energy: 1.3 eV, [[gamma]] [[proportional]][AsH3]-0.5 ). This is consistent with HCl etching (1.2 eV) where the arsenic removal kinetics limit the process . While, for AlAs, since y was around 3 times larger than the calculated value from the lattice contraction induced by C, we propose an alternative model for etching effect, in which Br in the form of the precursor Al-CBr reacts with the surface AlAs to remove Al as AlBr or AlAs molecules during C incorporation.
 J. S. Lee et al, J. Appl. Phys. 76 (1994) 5079.
 C. Su et al, Surf.Sci. 312 (1994) 181.
"Doping and In Situ Selective Etching of AlGaAs with CCl4 in Metalorganic Vapor Phase Epitaxy:" H.Q. HOU, B.E. Hammons, H.C. Chui, Sandia National Laboratories, MS 0603, Albuquerque, NM 87185
Carbon is a very attractive p-type dopant for GaAs and AlGaAs due to its low diffusivity and high solid solubility. In metalorganic vapor phase epitaxy (MOVPE) growth, the most common carbon dopant precursors are thermally cracked CCl4 or CBr4. For both precursors, the doping efficiency is reported to be fairly sensitive to the growth temperature, and is accompanied by a parasitic etchback by the halogen radicals. In this paper, we present results which indicate that the doping efficiency decreases by two orders of magnitude and etchback rate increases by a factor of 15 for AlxGa1-xAs when x changes from 1 to 0. The strong compositional selectivity of this doping and etching has a range of potential implications, particularly for novel devices involving regrowth on patterned surfaces.
Epitaxial growth was carried out in an Emcore GS3200 reactor. The C-doped AlGaAs was grown with TMG, TMA, CCl4 bubblers and 100% AsH3. The total reactor flow and pressure are 32.6 slm and 60 torr, respectively. The growth temperature varies from 620 to 750deg.C. Doping level was determined with Hall measurements, and growth and etchback rates were measured with an in situ normal incidence reflectance setup. The C doping in GaAs is approximately 4 times more efficient at the growth temperature of 640deg.C than at 750deg.C. However, the doping level changes from 2x1017 to 2x1019 cm-3 when the Al composition in AlGaAs changes from 0 to 1 even with the same CCl4 flow and growth temperature (750deg.C). On the other hand, the etchback rate at 750deg.C for GaAs is about 6 times more than that at 640deg.C. Furthermore, this etchback rate has a strong dependence on the Al composition in AlGaAs. The etchback rate for AlAs is approximately 15 times lower than that for GaAs. We will present a mechanism to qualitatively account for the strong dependence of the doping level and etchback rate on the Al composition in AlGaAs. We will also present some applications of this in situ selective etching approach.
In summary, CCl4 is a more efficient doping precursor at lower temperature (e.g. 640deg.C), and a unique in situ selective etchant at high temperature (e.g. 750deg.C) in AlxGa1-xAs.
This work is supported by the DOE under contract N0. DE-AC04-94AL85000
"Reduction of Dry Etching Damage with the Low Temperature GaAs as a Damage Blocking Layer:" CHING-HUI CHEN, James P. Ibbetson*, Xuehua Wu*, Evelyn L. Hu, Jim S. Speck*, Umesh K. Mishra, Department of Electrical and Computer Engineering, *Department of Materials, University of California, Santa Barbara, CA 93106
Ion damage produced during dry etching processing can lead to degraded electrical and optical properties of semiconductor devices. Through ion channeling and rapid defect diffusion, the damage range, even for 300eV ions, can extend more than 1000è into the substrate. Reducing ion-induced defects during semiconductor fabrication process is important for improving the device performance and long term reliability. In this work, we utilized a thin layer of annealed GaAs (-210è) grown at low temperature (LT-GaAs) as a damage blocking layer to minimize ion-induced defects.
The material structure considered in this study is a multiple quantum well (MQW) probe structure. Above the quantum wells, a thin layer of LT-GaAs (~210A) was grown at 250deg.C and 50A AlAs layers on each side of LT-GaAs act as a diffusion barriers for point defects during the subsequent thermal annealing. The other similar structure which differs only in the growth temperature of the top thin layer of GaAs ( at 600deg.C) was taken as the control sample. LT-GaAs capped samples annealed at 500deg.C, 60deg.C and 700deg.C, together with control samples, were exposed to the Ar+ ion beam for 3 minutes at beam energy of 500eV with an ion beam current of 50uA/cm2. The photoluminescence (PL) measurements were performed at 1.4 deg.K with argon laser excitation. A dramatic improvement in the photoluminescence was observed for samples capped with a thin layer of annealed LT-GaAs and the improvement in PL efficiency is related to the annealing temperature.
It has been previously established that for GaAs epilayers grown by Molecular Beam Epitaxy (MBE) at low temperature (200-300deg.C) and subsequently annealed at higher temperature (>500deg.C), the 1%-2% excess arsenic in the material forms precipitates embedded in a GaAs matrix. The size and density of the precipitous have a direct correlation with the annealing temperature. The presence of As precipitates in the thin layer of LT-GaAs, which was confirmed by TEM, could effectively prevent ion damage from penetrating into the substrate by dechanneling incident ions or gettering defects. Our results provide a potential application of LT-GaAs in reduction of ion damage created during dry etching process and underscore the importance of the microstructure of arsenic precipitates in LT-GaAs layers.
"Implant Activation and Residual Damage in C/Ga and Si-Implanted GaAs:" A.M. ANDREWS, S.T. Horng, M.S. Goorsky, University of California at Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1595
The relationship between residual implantation damage and the activation of implanted ions was addressed using triple axis x-ray diffractometry and Hall effect measurements with implanted semi-insulating GaAs substrates which were subject to different annealing temperatures. The experiment used a co-implant of carbon (5 x 1014 cm-2, 27 keV, room temperature) and gallium (5 x 1014 cm-2; 160 keV, room temperature) [the gallium provides the necessary lattice disorder] to generate the p-type samples and a silicon implant (1 x 10l3 cm-2; 90 keV, 80deg.C) for the n-type samples. For both p-type and ntype implants, we determined that full activation was only achieved after complete restoration of the lattice, which only occurred after annealing above =1000deg.C for 10 seconds. On the other hand, the mobility reached a maximum value at lower annealing temperatures (= 850deg.C), demonstrating that mobility is not as sensitive to residual damage as is implant activation. Diffuse scattering - as determined by the x-ray diffraction measurements - initially increased with annealing temperature and then decreased for higher annealing temperatures. The diffuse scatter increase at low temperatures is due to the organization of point defects into dislocation loops and other extended defects. The low levels of diffuse scatter after high temperature anneals (to levels comparable to the starting substrate) demonstrates that the formation of these defects is impaired, allowing for full implant activation.
"Thin Films InP-Based Quantum Electronics Integratead onto Si Substrates:" N. EVERS, O. Vendier, C. Chun, M.R. Murti, J. Laskar, N.M. Jokerst, School of Electrical and Computer Engineering, Microelectronics Research Center, Atlanta, GA 30332-0250; T.S. Moise, Y.-C. Kao, Corporate Research and Development, Texas Instruments, Inc., MS-134, 13588 N. Central Exp., PO Box 658936, Dallas, TX 75265
We report thin film InP based resonant tunneling diodes (RTD) and tunneling hot electron transfer amplifiers (THETA) contact bonded to silicon substates. Pseudomorphic AlAs/In0.53Ga0.47As/InAs resonant tunneling diode structures grown on semi-insulating InP with peak-to-valley current ratios (PVR) as high as 30 at 300 K have been separated from the growth substrate and bonded to silicon substrates coated with Si3N4, forming thin film devices. In addition, thin film multiple stack RTD structures have been bonded to silicon substrates. The I-V characteristics of both the single and multi-stacked thin film RTDs exhibit no signs of degradation after bonding to the host substrate. The DC and RF characteristics of the THETA device have been determined for before and after substrate removal and contact bonding. The DC characteristics of the thin film device are maintained after substrate removal and bonding. A study of the RF characteristics of the thin film THETA structures is under investigation with various substrates, including: silicon covered with a 5000Å Si3N4, glass, and quartz. Initial results indicate comparable RF performance can be achieved between before and after contact bonding.
These results are the first successful demonstration of high performance InP
based electronics bonded to a silicon host substrate. We present the highest
PVRs reported to date on silicon, and present the first RF performance results
of thin film InP quantum electronics.
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