Study of Short- and Long-Term Effectiveness of Ammonium Sulfide as Surface Passivation for InAs/GaSb Superlattices Using X-Ray Photoelectron Spectroscopy
The surface quality of as-etched and ammonium sulfide [(NH4)2S]-treated samples of an indium arsenide/gallium antimonide (InAs/GaSb) superlattice structure were compared using x-ray photoelectron spectroscopy (XPS). After short exposure to the atmosphere following passivation, treated samples displayed a complete absence or significant reduction of native oxides compared with untreated samples, confirming better quality of surface passivation. However, extensive sulfidization was not observed, and after extended exposure, the native oxides reappeared on the treated surface, establishing the need for a capping layer for long-term passivation stability. The surface study provides definitive confirmation of previous results on electrical properties of photodetectors fabricated on InAs/GaSb superlattices.