Study of GaAs as a material for solar neutrino detectors

Semi-insulating GaAs crystals grown by liquid encapsulated Czochralski tech nique from Ga-rich melts were evaluated as a possible material for radiatio n detectors with a high active layer thickness. The density of deep traps, particularly the midgap EL2 donors pinning the Fermi level, was measured by various techniques in conducting and semi-insulating samples. For EL2 trap s, a direct evidence of their partial neutralization in the space charge re gion of reverse biased Schottky diodes due to nonequilibrium capture of ele ctrons is presented for the first time. It is shown that the density of EL2 centers decreases with decreased As composition of the melt very gradually , especially for post-growth annealed samples. Subsequently, if one aims to decrease the EL2 density to such an extent that it would make a serious im pact on the depletion layer width in GaAs-based detectors one has to grow s emi-insulating GaAs crystals from melts with As composition below about 43% which poses a problem for the preservation of high resistivity of the mate rial due to the relatively high concentration of compensating accepters. (C ) 2000 Elsevier Science B.V. All rights reserved.