Voltage-tunable dual-band infrared photodetectors with Si/SiGe metal-semiconductor-metal heterostructure

A simple and low-cost structure of voltage-tunable dual-band near-infrared photodetector (PD) has been proposed, in which the PDs were developed by using Si_0.8Ge_0.2/Si metal-semiconductor-metal (MSM) heterostructure. The Si_0.8Ge_0.2/Si layers were deposited by ultrahigh-vacuum chemical vapor deposition system and a transparent layer of indium-tin oxide (ITO) was used as a metal layer to enhance the entrance of photons. In this study, we found that only one band was detected with a peak wavelength located at 950 nm at zero applied bias. When bias was increased to 1 V, in contrast a dual-band was achieved, where two peak wavelengths were centered at 950- and 1150-nm. It is suggested that the two bands are the absorption of top-Si and bottom-Si_0.8Ge_0.2 layers, respectively. The spectra of Si bulk and Si_0.8Ge_0.2 layer were also measured to verify our results and relating mechanisms are explained here.