Molecular beam epitaxy grown Al(Ga)InAs: Schottky contacts and deep levels

The authors have investigated methods of preparing high quality Schottky contacts on Al(Ga)InAs grown on InP substrates. A new kind of surface treatment (2 nm GaAs cap layer, phosphoric acid-based etching) before metal evaporation was developed. Barrier heights up to 0.73 eV and low leakage current densities of 0.22 mu A/mm2 (about one order of magnitude lower than without treatment) have been attained. The quality and stability of these contacts were mainly affected by a surface treatment, but only a slight dependence on doping and on the choice of metallization was observed. Si-doped AlInAs and AlxGayIn1-x-yAs(x+y approximately=0.48) bulk material with different gallium contents are analyzed by deep level transient spectroscopy. Overlapping alloy broadened trap responses are separated by numerical spectrum analysis and reduction of the filling pulse width. They ascertained that the deep level concentration of AlxGayIn1-x-yAs is decreasing with increasing gallium content (by a factor of two from y=0 to y=0.12). This fact is associated with an improved crystalline quality of the quaternary AlGaInAs material, compared to ternary AlInAs, as demonstrated by narrow X-ray diffraction peaks and photoluminescence linewidths.