Multiple-energy proton bombardment in n+-GaAs

The effects of single-energy and multiple-energy proton bombardment on the electrical characteristics of n⁺-GaAs (n ≥ 10¹⁸ cm^?3) have been studied. It was found that a multiple-energy bombardment is superior to a single-energy bombardment in creating high-resistivity layers in n⁺-GaAs. For 4 × 10¹⁸ cm^?3 GaAs, the entire 4-μm-thick bombarded layer could not be effectively compensated by a single-energy 400-keV bombardment. A multiple-energy bombardment, however, effectively compensated the bombarded layer throughout its depth. With no annealing, there is a optimum multiple-bombardment dose which maximizes the average resistivity. With annealing, higher doses are necessary and for a dose higher than the optimum without annealing, the resistivity at first increases and then goes through a maximum with increasing anneal temperature. There is again an optimum dose for any specific anneal temperature and for the range of doses studied, the resistivity reaches a maximum at a higher anneal temperature for increasing total dose. For n⁺-GaAs with an initial concentration of 10¹⁸ cm^?3, layers with an average resistivity of $\text{≥ 10}{}^8\text{Ω-}\text{cm}$ have been achieved using a multiple-energy bombardment and an anneal temperature as high as 500°C. Measurement of the ac resistivity as a function of frequency indicates that conduction in the bombarded layer may be occurring via a hopping mechanism.