PASSIVATION OF SHALLOW AND DEEP LEVELS BY LITHIUM IN GAAS

Similar to hydrogen the group-I element lithium passivates various shallow and deep levels in GaAs. In p-type GaAs lithium passivates the shallow accepters Zn-Ga and Cd-Ga and the deep acceptor Cu-Ga. In n-type GaAs it passivates native deep donors such as EL2 and EL6. However, in contrast to hydrogen there is no evidence of the passivation of shallow donors by lithium in GaAs. The passivation of shallow accepters in p-type GaAs is inferred from a simultaneous increase of the Hall hole mobility and decrease in free carrier concentration throughout the bulk of Li-diffused samples. The accepters can be reactivated by thermal annealing. We attribute the passivation to the formation of neutral Li-Zn and Li-Cd complexes. The passivation of Cu-Ga is concluded from the disappearance of deep level transient spectroscopy (DLTS) signals due to the Cu-Ga acceptor levels at E(v) + 0.15 and E(v) + 0.40 eV when the material is diffused with Li. A similar disappearance is observed for the well known PL band at 1.36 eV also attributed to the Cu,, defect. Both DLTS and PL signals can be reactivated by thermal annealing. Passivation of the native deep donors EL2 and EL3 in n-type GaAs is concluded from the reduction of the relevant peak heights in DLTS spectra after Li-diffusion. The defects can be reactivated by thermal annealing.