MIDGAP STATES IN METALORGANIC VAPOR-PHASE EPITAXY GROWN ALXGA1-XAS

The electrical properties of midgap states in n-type AlxGa 1-xAs grown by the metalorganic vapor phase epitaxy were investigated by the deep level transient spectroscopy and photocapacitance (PHCAP) techniques. A new PHCAP measurement procedure to avoid interference from the photoionization of the DX center was used. Two near-midgap levels, i.e., a higher lying MH level and a lower lying ML level were detected. As AlAs mole fraction, x, is increased, the energy positions of these two levels became deeper, maintaining a remarkable horizontal alignment with respect to the hybrid orbital energy level. The ML level showed a clear photoquenching for x<0.3, but the quenching disappeared for x≳0.3. No photoquenching of the MH level was observed for all x investigated. Similarity of the photoquenching behavior to GaAs1-x Px as well as its energy position and optical cross sections led to the conclusion that the ML level is an As-related EL2-like defect. On the other hand, the MH level originates from a defect related to Al.