DX Centers in AlGaAs

Abstract: This thesis presents a study of DX center related phenomena in silicon doped AlGaAs and in GaAs/AlGaAs multi-layer structures. A variety of experimental techniques such as capacitance-voltage (C-V), deep level transient spectroscopy (DLTS), single shot capacitance, thermally stimulated capacitance (TSCAP), admittance spectroscopy, photocapacitance, and photoconductivity have been used. The main results can be summarized as follows: (1) Multiple DX levels were observed in AlGaAs. They exhibit different emission and capture barriers, and different electric field dependence of the electron emission rate. (2) DX centers were found to give rise to unusual features in C-V measurements due to their large concentrations. The C-V measurements of Schottky diodes fabricated on AlGaAs were analyzed for both high and low frequencies, and a transient C-V method was proposed. The experimental results were fitted by using the statistics for the positive-U and negative-U models of DX centers. (3) Three metastable states of the Si donor related to different donor configurations were observed in AlGaAs. (4) From photocapacitance measurements deep energy levels in the lower half of the band gap were observed in molecular beam epitaxy (MBE) grown AlGaAs. Possible influence of their presence in photoexcitation experiments performed to characterize DX centers has been discussed. (5) Transport and defect-related properties in GaAs/Al(0.33)Ga(0.67)As multi-layer structures have been investigated in detail. No DX center related features were observed in these structures.