Nondestructive characterization of oxide/germanium interface by direct-gap photoluminescence analysis

We demonstrate that direct-gap photoluminescence (PL) analysis is useful for the nondestructive, fast, and in-line characterization of the oxide/ germanium (Ge) interface without making actual devices. The fact that Ge has a quasi-direct gap enables us to utilize direct-gap PL intensity as a good indicator for interface quality estimation. We experimentally confirm the validity of the present analysis, by comparing PL spectra with capacitance-voltage characteristics. The impact of the band bending at the interface on PL intensity is also discussed. Furthermore, the effect of forming gas annealing at oxide/Ge interfaces is discussed by taking advantage of the present method.