Application of dopant segregation to metal-germanium-metal photodetectors and its dark current suppression mechanism

We report the mechanism of dopant-segregation (DS) technique as applied in metal-germanium-metal photodetectors (MGM-PDs) for dark current suppression. Photodetectors with various dopant-segregation strategies were designed, fabricated, and characterized. Results show that asymmetric MGM-PD, with n - and p -type dopants segregated separately in two NiGe electrodes, is the optimized scheme in terms of dark current and responsivity. It shows a dark current of 10-6 A at -1 V, which is two to three orders of magnitude lower than that of MGM-PD without DS. n -type dopant (As) segregation in NiGe barrier increases the hole Schottky barrier height to 0.5 eV and, thus, plays a crucial role in dark current suppression.