Defects, their Interaction and Modification by Irradiation in Semi-Insulating GaAs

Abstract

We investigated Semi-Insulating (SI) GaAs Schottky diode particle detectors, fabricated either on single SI-GaAs LEC crystals, or on VPE layers from several suppliers, before and after irradiation with high-energy protons and pions. A detailed comparative analysis of thermally stimulated current (TSC) and depolarisation current (TSD) spectra have been made. To separate the single traps, we used their thermal emptying by fractional heating. The following main conclusions are drawn. First of all, many different levels (from 8 by 12) have been found in the temperature range from 90 K to 300 K in all samples. Their activation energies range from 0.07 up to 0.55 eV, their capture cross sections are 10 -22 - 10 -14 cm 2 , and initial occupation is 2×10 11 - 5×10 14 cm -3 . The irradiation with pions and protons does not influence the density of most levels significantly. On the other hand, levels with activation energies of about 0.07 - 0.11 eV, 0.33 - 0.36 eV, 0.4 - 0.42 eV, and 0.48 - 0.55 eV have been found only in the irradiated samples. Furthermore, peculiarities of the TSC were observed that could not be explained by a homogeneous semiconductor model. The existence of different polarisation sources in different temperature ranges is also demonstrated by TSD. Irradiation increases the inhomogeneity of the crystals, causing the scattering of the activation energies. A model of the reconstruction of dislocation net under irradiation is proposed, which foresees formation of different (p-type) conductivity channels around dislocations through the metastable transformation of the EL2 level.