The electron and hole traps in semi-insulating (SI) GaAs can not be identified by common Photoinduced Current Transient Spectroscopy (PITS) and Thermally Stimulated Current (TSC) measurements because of appearing of same sign signal for electrons and holes in both experiments. Therefore, we have developed two approaches which could be used to identify the type of the traps, and the origin of the puzzling negative peaks in the PITS spectra.
The TSC and qusi-stationary Hall effect measurements have been simultaneously performed at the temperatures between 77K and 300K. The sign of Hall voltage corresponding to TSC peak shows the type of the trap.
PITS spectra with applying different bias polarity to the sample were carefully measured with below gap and above gap photoexcitation. According to the change of PITS peak's height with different bias polarity, the electron and hole traps could be readily distinguished, since a negative bias makes hole no contribution to the PITS signal whereas electron swept into the sample would fill the electron traps, and consequently results in the appearence of the electron trap peaks. On the contrary, a positive bias would cause the filling of the hole traps.
The negative PITS peaks appearing or vanishing can be understood if one takes into account the trap initial filling conditions, the carrier recapture and the high dark current etc.