Relation between Cr-Level and Main Electron Trap (EL2) in Boat-Grown Bulk GaAs

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Abstract
In order to characterize the Cr (Chromium)-level in bulk GaAs, a normal DLTS method was applied to boat-grown bulk GaAs which was Cr- and O (Oxygen)-doped but did not become semi-insulating. In the lightly-compensated region, no Cr signal was observed, probably because it is covered by the signal from the main electron trap EL2. In the moderately-compensated region, both signals of Cr and El2 were observed, but the trap concentration of EL2 was greatly reduced. In the heavily-compensated region, a large Cr-trap signal was observed, but no signal of EL2 could be observed even when the minority carrier injection was suppressed. Since Cr occupies a Ga site and forms deep acceptors, these results can be understood by considering that the Cr doping reduces the number of Ga vacancies and as a result the number of main electron traps EL2 which are produced by a Ga deficit is also reduced.