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Combining electron paramagnetic resonance under optical excitation, deep level transient spectroscopy, electron irradiation, annealing, and quenching on LEC semi-insulating GaAs and lightly Si-doped material grown in the same way as the semi-insulating material, we have shown that (i) the irradiated material contains two types of defects related to the antisite AsGa, one As∇Ga, present before irradiation, identified to EL2 from its characteristic photoquenching behavior and the other As*Ga, created by the irradiation, stable under photoexcitation; (ii) As∇Ga anneals partially under a 850 °C thermal treatment followed by a quench and the remaining defects are transformed into As*Ga; (iii) further annealing around 120 °C converts As*Ga into As∇Ga, the process being thermally activated (0.5±0.2 eV). From these results and using observations of absorption on vibrational modes of the C-As interstitial pair in electron irradiated material, we are able to conclude that As*Ga is the isolated antisite and As∇Ga, i.e., EL2, is a complex of an As antisite and an As interstitial.

A novel semiclosed diffusion technique for III-V semiconductors has been developed giving ease of control of the operating and junction depth. The secondary-ion mass-spectrometry atom profiles and carrier-concentration profiles have been used to develop a mechanism involving the temperature dependence of neutral Zn formation. Doubly-ionized interstitials are thought to be the diffusion species.

Quantitative Cr profiles have been determined on semi-insulating GaAs by secondary-ion mass spectrometry (CAMECA IMS 300). It is shown that after thermal annealing (900 °C, 20 min) under Si3N4, Cr diffuses towards the GaAs surface, leaving a Cr concentration depletion zone underneath. This zone becomes conductive with a carrier concentration of n∼2×1016 cm−3. Some consequences of these findings are considered.