Post-etching mesa surface composition investigation of InAs/GaSb type-II strained layer superlattices using XPS characterization

• InAs/GaSb superlattice p-i-n and bulk samples were fabricated to compare H3PO4-based and HCl-based treatments.
• Spectral and imaging X-ray photoelectron spectroscopy (XPS) analysis were performed on the bulk sample.
• Dark current measurements were performed on the p-i-n sample.
• XPS and electrical characterization results were compared.

XPS characterization was used to determine the surface chemistry of a mid-wave infrared T2SL treated by both an HCl-based and an H3PO4-based etching solution. This analysis, performed over both the etched and unetched portions of the sample, revealed that the HCl-based etch removed Ga and Sb oxides while the H3PO4-based etch removed In and As oxides. XPS imaging was also done on 200 μm × 200 μm areas of the sample, and showed that HCl solution (Ga, and O) produced surfaces that were less stoichiometric than the H3PO4 solution (Ga2O3, Sb2O5, Sb in GaSb). Single-pixel, p-i-n test structures were fabricated using either etching solution, and an electrical comparison revealed over an order of magnitude improvement in dark current for the sample treated with the H3PO4 solution, compared to the HCl sample.