Effects of metal/Ge contact and surface passivation on direct band gap light emission and detection for asymmetric metal/Ge/metal diodes

Direct band gap electroluminescence (EL) and light detection were studied at room temperature for n-type bulk germanium (Ge) by using fin-type asymmetric lateral metal/Ge/metal diodes. HfGe/Ge and PtGe/Ge contacts were used for injecting holes. Electron cyclotron resonance plasma oxidation and physical vapor deposition bilayer passivation (BLP) methods were employed for passivating the surface of the active region. A high EL intensity and a low dark current intensity were observed for the sample with PtGe/Ge contact and BLP, owing to the small/large barrier height of holes/electrons for PtGe/Ge contact, respectively, and the low density of interface states for the active region with BLP. The local-heatinginduced redshift of the EL peak for the sample with PtGe/Ge contact is smaller than that for the sample with HfGe/Ge contact, owing to the lower parasitic resistance of PtGe/Ge contact. The diode with PtGe/Ge contact and BLP shows an on/off ratio of >104 and a responsivity of 0.70A/W, corresponding to an external quantum efficiency of 56.0% under a wavelength of 1.55 μm.