Electronic and optoelectronic characterization of Au Schottky barrier contacts on MOCVD grown (1) GaAs/Ge, (2) GaAs/Ge/Si and (3) GaAs/Si

An experimental study has been performed on the electronic and optoelectronic properties of rectifying Au Schottky Barrier contacts on MOCVD grown GaAs (1) on bulk Ge, (2) on Si coated with Ge and (3) directly on Si. The electrical properties were studied by current vs. voltage (I-V) and capacitance vs. voltage (C-V) measurement. Their photoresponse was tested with 0.87 µm and 1.3 µm laser diodes. The results indicate that the GaAs/Ge structure has the best I-V characteristic with ideality (n) factor very close to unity in the forward region and good reverse bias saturation. All three structures have uniform doping (in 1E15 to 5E16 cm-3 range) profile near the GaAs surface. They become highly doped in regions near the hetero-junction (GaAs-Ge, GaAs-Si or Ge-Si) interfaces. At 0.87µm quantum efficiencies (Q. E.) of 11%, 8% and 8.67% were observed for the GaAs/Ge, GaAs/Ge/Si and GaAs/Si samples, respectively. At 1.3µm, only a low level of photoresponse was observed. This work represents the first comparative study on the properties of III-V (GaAs) on Si hetero-junction devices fabricated by direct and indirect MOCVD growth processes. The results are of considerable significance in understanding the effect of Ge, Si and As interdiffusion on the properties of the hetero-epitaxial GaAs layer grown on Si substrate.