Open AccessSuppression of dark current in GeO_x-passivated germanium metal-semiconductor-metal photodetector by plasma post-oxidation
Author(s) -
Jian Kang,
Rui Zhang,
Mitsuru Takenaka,
Shinichi Takagi
Publication year - 2015
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.23.016967
Subject(s) - passivation , dark current , materials science , germanium , optoelectronics , photodetector , diode , semiconductor , schottky barrier , surface states , analytical chemistry (journal) , layer (electronics) , silicon , nanotechnology , chemistry , surface (topology) , geometry , mathematics , chromatography
We propose GeOx passivation by plasma post-oxidation for dark-current suppression in a germanium (Ge) photodetector (PD). A GeOx/Ge interface exhibits a significantly lower interface trap density than SiO2/Ge and Al2O3/Ge interfaces. GeOx passivation on a Ni/Ge Schottky diode decreases the dark current under -1 V bias by more than one order of magnitude compared with Al2O3 passivation, which is attributed to the reduction in the surface leakage current. We also evaluated the Ge surface potential to study its effect on the surface leakage current. It was found that the surface leakage is suppressed when the accumulation condition of the Ge surface is enhanced as a result of fixed charges in the passivation layer. Thus, we have revealed the importance of a low interface trap density at the Ge surface and a suitable number of fixed charges in the passivation layer for achieving a low dark current in Ge metal-semiconductor-metal (MSM) PDs. Finally, we have examined the effect of GeOx passivation on a normal-incidence Ge MSM PD. We observed a significant decrease in the dark current in the GeOx-passivated samples, and a dark current of 97 nA under -1 V bias was achieved under the optimal GeOx passivation conditions.