DONOR-RELATED DEEP LEVELS IN HEAVILY SE-DOPED ALXGA1-XAS

The effects of donor-related deep levels on the doping characteristic and photoluminescence in Se-doped AlGaAs grown by metalorganic chemical vapor deposition have been studied. The net donor concentration has been observed to increase in proportion to doping in GaAs and Al0.4Ga0.6As, showing a cube-root dependence in Al0.1Ga0.9As in the high doping concentration range. In a photoluminescence study, the emission due to self-activated (SA) centers, which are complexes comprising a donor atom and a group-III vacancy, was observed in Al0.1Ga0.9As with a stronger intensity than in GaAs. It is therefore suggested that more serious compensation in Al0.1Ga0.9As than in GaAs by SA centers is responsible for the early beginning of the cube-root dependence in Al0.1Ga0.9As. In addition, the emission energy of SA centers was studied as a function of the carrier concentration; the observation of a Burstein-Moss shift in the SA emission energy reveals that it is due to a band-to-acceptor transition. In the case of Al0.4Ga0.6As, since no SA emission was observed, the linear increase in the net donor concentration up to high density has been interpreted as being the result of the absence of SA centers. The mechanism which suppresses the formation of SA centers in Al0.4Ga0.6As is discussed in conjunction with DX centers. A new luminescence band associated with DX centers was observed in Al0.4Ga0.6As; its emission mechanism is also discussed.