Experimental evidence for the distinction between metastability and persistence in optical and electronic properties of bulk GaAs and AlGaAs

In this paper we present experimental evidence supporting that persistent b ehavior in the electronic and optical properties of bulk GaAs and AlGaAs ca n have different origins as: the metastability of a defect, the persistent charge transfer from a defect to another defect, and the transfer from a de fect to the conduction band. In particular, we show three different cases i n which defects are either directly or indirectly related to persistent cha nges of the optical absorption, the magnetic circular dichroism of the abso rption (MCDA) and the photoconductivity (PC),The three cases are as follows : the transfer of EL2 to the metastable state EL2(0)* in semi-insulating (S I) GaAs causing persistent quenching of the absorption and photoconductivit y (PPCQ); the persistent transfer of electrons from stable EL2(0) to arseni c vacancies in lightly n-type GaAs; and the correlated appearance of persis tent MCDA and photoconductivity in AlGaAs due to the photoionization of DX- centers.