Semi-insulating LEC GaAs as a material for radiation detectors: materials science issues

Semi-insulating (SI) GaAs is now being reconsidered as a promising material for radiation detectors, mostly due to greatly improved quality of the mat erial. In this paper we shall describe the properties of the state-of-the-a rt SI GaAs crystals grown by LEC method as relevant for such applications. Specifically, we shall concentrate on the assessment of the spectra and den sity of residual impurities, on the measurements of deep levels spectra and on studying the impact of these centers on material parameters. The spectr a of deep centers as studied by PICTS and DLTS indicate that, in LEC crysta ls grown from stoichiometric melts, besides the most prominent EL2 center, other electron and hole traps are usually observed. By comparing the DLTS a nd PICTS results we show that PICTS often tends to overestimate the relativ e contributions of traps shallower than EL2. Two approaches to decreasing E L2 concentration in LEC grown crystals have been proposed in literature: to grow crystals from Ga-rich melts and to anneal the material at high temper atures. We have studied the changes in deep level spectra and transport par ameters for both cases. In annealing experiments the possibility of thick s amples modification by arsenic diffusion was also investigated. (C) 2001 El sevier Science B.V. All rights reserved.