Growth, optical, and electron transport studies across isotype n-GaAs/n-Ge heterojunctions

A diode structure consisting of a polar epilayer on a nonpolar substrate grown by metalorganic vapor phase epitaxy often faces problems of antiphase domain formation in the polar semiconductor and cross diffusion across the heterointerface. Ge outdiffusion into GaAs epilayers was studied by low temperature photoluminescence spectroscopy after etching the film from the surface. The absence of p-n junction formation inside the Ge substrate from interdiffusion of Ga and As has been studied by current-voltage characteristics using mesa diodes. These observations were confirmed by electrochemical capacitance voltage polaron profiler and secondary ion mass spectroscopy techniques. To understand the material quality and current conduction mechanism across the GaAs/Ge heterojunction, I-V characteristics of Si-doped n-GaAs/n-Ge isotype heterojunctions using Au Schottky diodes have been studied for different doping densities. A plethora of growth conditions appear in the literature concerning the attempt to grow antiphase domain (APD)-free GaAs on Ge. In the present case, even though the growth temperature regime is close to reported values, the main difference in minimizing APD formation may arise from the growth rates (~ 3 µm/h) and the V/III ratio (~ 88).