In addition to the persistent photoconductivity (PPC) attributed to DX
centers in GaAs delta-doped with Si, a weak PPC (WPPC) with a PPC car
rier density independent of Si-doping concentration has been generally
reported at ambient atmosphere, but the nature of the deep states res
ponsible has not been elucidated. Here, we present the results of a de
tailed study of the WPPC in delta-GaAs: Si at low-doping densities, N-
Si approximate to 1-3 x 10(12) cm(-2), and ambient pressure. It is con
cluded that the WPPC does not arise from DX centers but from another d
eep defect, which is DX-like in the sense that it can be metastably ex
cited. The presence of two distinct DX-like states is apparent from tw
o separate annealing temperatures of the PPC, T-a approximate to 50 K
and T-b approximate to 230 K; to the best of our knowledge, the latter
is the highest annealing temperature observed in the AlGaAs: Si syste
m. (C) 1998 American Institute of Physics. [S0003-6951(98)00148-X].