A combined high‐resolution electron microscopy, x‐ray photoemission spectroscopy, and electrical properties study of the InP–SiO₂ interface

The InP‐native oxide‐SiO₂ interface system has been studied by cross sectional high‐resolution electron microscopy (HREM), x‐ray photoemission spectroscopy (XPS) depth profiling, and C‐V and G‐V measurements. The devices were prepared on InP treated in several different ways, including InP oxidized in air at about 350 °C for 68 h. HREM shows that the interface roughness varies, depending on the InP surface treatment, from <5 Å for InP treated in a solution of KOH in methanol to >100 Å for InP etched in iodic acid. Ellipsometry measurements on as‐cleaned InP indicate a native oxide of 9 to 15 Å thickness, but no such oxide is clearly evident in HREM images. For the thermal oxide ellipsometry gives a thickness of 107 Å, and HREM shows an oxide of ∼110 Å thickness between the InP and the SiO₂. HREM further shows that the thermal oxide consists of an inner layer (next to InP) about 50 Å thick and an outer layer about 60 Å thick, and that the oxidation roughens the InP substrate to a depth of 30–50 Å. XPS suggests that the inner oxide layer is primarily InPO₄, while the outer layer is rich in In₂O₃. Finally, some correlations are established with the electrical properties: thin native oxides lead to lower interface state densities than the thick thermal one, but the roughness of the interface does not, at present, appear to adversely affect the electrical results.