Characterizing junction profiles in Ge photodetectors using scanning capacitance microscopy (SCM) and electron holography

Abstract

Scanning Capacitance Microscopy (SCM) and dual lens electron holography have been used to investigate poor responsivity in germanium p-i-n photodetectors by measuring the carrier profiles and electric potential, respectively. For one case study, SCM results revealed two significant observations in a poor responsivity photodetector: (1) a shifting junction position across the intrinsic region at different cross sectional planes of the diode, (2) the intrinsic region is lowly doped and exhibits a 'folded' junction geometry, namely, the intrinsic region consists of p-type carriers along the edges while n-type dominates the central portion. On the other hand, Holography results revealed a narrow intrinsic region than designed and an insignificant difference in width between good and poor responsivity photodetectors.