Semi-insulating GaAs substrates doped with chromium were implanted with 120-160 ke V28Si+ ions (1012-1013 cm-2 at room temperature. After thermal annealing, the carrier concentration and mobility profiles, residual damage and impurity levels of implanted wafer were determined by C-V method, back scattering technique and photo-1uminescence spectra. The results showed that the semi-insulating GaAs substrate selection and 28Si+ beam purity control are necessary to obtain reproducible and high activation implantation. Fabricated with multiple localized silicon implantation for both active and contact layer, GaAs dual-gate MES FET applicated in UHF TV tuner reached a noise figure of 0.9 dB and an associated gain of 10 dB at 1 GHz. The mobility profile and appropriate annealing temperature are discussed on the basis of the present experimental results.

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We studied the carrier profile tail formed in GaAs materials of 28Si+ implanting into Cr-doped semi-insulating substrate, including the effects of annealing temperature and time. The effects of carrier profile tail on GaAs MESFET output characteristics simulated by computer were in accord with measured results, indicating that the profile tail does make the abnormal output characteristics in MESFET. The origin of profile tail in connection with Si background in GaAs substrate and Cr redistribution during high temperature annealing was discussed.