Damage Distribution Studies in Proton-Implanted GaAs
- PDF / 1,456,336 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 14 Downloads / 250 Views
DAMAGE DISTRIBUTION STUDIES IN PROTON-IMPLANTED GaAs H. A. JENKINSON, M. O'TOONI, J. M. ZAVADA, T. J. HAAR U. S. Army Armaments Research and Development Center, Dover, NJ 07801 and D. C. LARSON Drexel University, Philadelphia, PA 19104 ABSTRACT Samples of n+-GaAs implanted with 300 keV protons have been examined using high resolution electron microscopy, capacitance-voltage profilometry, and infrared reflectance. In contrast to previously reported results, electron microscopic examination of the as-implanted samples revealed the presence of dislocation loops and/or precipitates both near the wafer surface and at the bottom of the implanted layer. These results are corroborated by electrical and optical measurements. INTRODUCTION Ion implantation is a technique which has been used to alter the refractive index of transparent dielectrics and semiconductors in order to form optical waveguides. The mechanisms by which the implanted ions achieve this effect are generally classified as either changes to the density or polarizability of the initial material, chemical doping, or carrier compensation [1]. Although all of these processes can occur simultaneously, usually one will predominate depending on the selection of target material and ion species. In highly doped semiconductors, the refractive index is depressed from that of the lattice by the free carrier plasma contribution to the dielectric function. The damage created in such a material during ion implantation can be used to trap the free carriers, allowing the refractive index in the damaged layer to rise towards the value it would attain in intrinsic material. In an effort to understand the mechanisms involved in modifying the refractive index of n-GaAs through proton implantation, irradiated samples have been examined using high resolution electron microscopy, capacitancevoltage profilometry, and infrared reflectance. Although the point defects believed to be responsible for carrier compensation are too small to be resolved by electron microscopy, examination of the samples using this technique was performed to determine the degree of crystallinity of the implanted layer and to look for defect agglomerations, such as loops and precipitates, which might indicate that excess damage was induced. The actual carrier compensation achieved was determined electrically by profiling the carrier concentration within the implanted layer using standard capacitance-voltage profiling techniques. Differential infrared reflectance measurements were performed to assess the effects of the implantation on the optical properties of the samples. SAMPLE PREPARATION The GaAs wafers used in these experiments were obtained from Laser Diode Laboratories. They were doped with Si to produce n-type material with Mat.
Res. Soc. Symp. Proc. Vol.
27 (1984) @Eleevier Science Publishing Co.,
Inc.
378
a carrier concentration of 3-4xlOI 8 /cm3 and a relatively high mobility of The wafers were oriented to expose (100) surfaces, which 1700 cm2 /V-sec. were optically polished by the manufacturer
Data Loading...
