A systematic study of (NH₄) ₂ S passivation (22%, 10%, 5%, or 1%) on the interface properties of the Al₂ O₃ / In_0.53 Ga_0.47 As/InP system for n -type and p -type In_0.53 Ga_0.47 As epitaxial layers

In this work, we present the results of an investigation into the effectiveness of varying ammonium sulphide (NH₄) ₂ S concentrations in the passivation of n -type and p -type In_0.53 Ga_0.47 As. Samples were degreased and immersed in aqueous (NH ₄) ₂ S solutions of concentrations 22%, 10%, 5%, or 1% for 20 min at 295 K, immediately prior to atomic layer deposition of Al₂ O₃. Multi-frequency capacitance-voltage (C-V) results on capacitor structures indicate that the lowest frequency dispersion over the bias range examined occurs for n -type and p -type devices treated with the 10% (NH ₄) ₂ S solution. The deleterious effect on device behavior of increased ambient exposure time after removal from 10% (NH₄) ₂ S solution is also presented. Estimations of the interface state defect density (Dit) for the optimum 10% (NH₄) ₂ S passivated In0.53 Ga0.47 As devices extracted using an approximation to the conductance method, and also extracted using the temperature-modified high-low frequency C-V method, indicate that the same defect is present over n -type and p -type devices having an integrated Dit of ∼2.5× 1012 cm-2 (±1× 1012 cm-2) with the peak density positioned in the middle of the In0.53 Ga0.47 As band gap at approximately 0.37 eV (±0.03 eV) from the valence band edge. Both methods used for extracting Dit show very good agreement, providing evidence to support that the conductance method can be applied to devices incorporating high- k oxides on In0.53 Ga0.47 As.