Noise performance of high-efficiency germanium quantum dot photodetectors

Abstract

We report on the noise analysis of high performance germanium quantum dot (Ge QD) photodetectors with responsivity up to $2 A/W and internal quantum efficiency up to $400%, over the 400-1100 nm wavelength range and at a reverse bias of À10 V. Photolithography was performed to define variable active-area devices that show suppressed dark current, leading to a higher signal-to-noise ratio, up to 10 5 , and specific detectivity D Ã ' 6 Â 10 12 cm Hz 1=2 W À1. These figures of merit suggest Ge QDs as a promising alternative material for high-performance photodetectors working in the visible to near-infrared spectral range.

Low‐Temperature Operation of High‐Efficiency Germanium Quantum Dot Photodetectors in the Visible and Near Infrared

“…The photodetectors were fabricated by co‐sputtering of Ge and SiO 2 targets on p − (5–10 Ω cm) Si substrates held at a temperature of 400 °C yielding a 200 nm‐thick oxide matrix with embedded Ge QDs . Following deposition the samples were annealed at 500 °C in a N 2 environment for 30 min to generate larger size and higher density Ge QDs with improved crystalline quality . Subsequently, an optically transparent, highly‐conductive ∼100 nm‐thick indium tin oxide (ITO) layer was sputter‐deposited as the top electrode.…”

“…Subsequently, an optically transparent, highly‐conductive ∼100 nm‐thick indium tin oxide (ITO) layer was sputter‐deposited as the top electrode. Photolithography was then performed to define several 1 mm 2 active area devices, obtained by etching away the ITO and Ge QD/SiO 2 layers using a dilute HF solution, with the aim of suppressing leakage current on the periphery as described in our previous work . Subsequently, an indium back contact was used to attach the detector onto a 0.5 mm thick sapphire (Al 2 O 3 ) substrate.…”

“…As extracted from Figure , at 300 K and −10 V of reverse bias the photodetector exhibits a spectral responsivity (R sp ) of 1.2 A W −1 , external quantum efficiency (EQE) of 226% and internal quantum efficiency (IQE) of 228% calculated for reflectance equal to 0.87% at 640 nm as presented in Ref. . As previously reported, the photoconductive gain mechanism responsible for EQE above 100% arises from the asymmetry in carrier transport: the much heavier tunneling mass of holes slows down their percolation through the Ge QDs, resulting in an effective positive charge in the QDs that favors the flow of the lighter electrons.…”

“…Typically, Ge photodetectors are operated at cryogenic temperatures in order to suppress the dark current, arising from thermally‐generated carriers due to its smaller bandgap. In this work we have studied the temperature‐dependent photoresponse and noise performance over the 100–300 K range in the visible and near‐IR, of CMOS‐compatible PDs based on Ge QDs embedded in an SiO 2 matrix as introduced in our previous work …”

Deep Level Assessment of n-Type Si/SiO2Metal-Oxide-Semiconductor Capacitors with Embedded Ge Quantum Dots

“…[3][4][5] In the former case, the QDs can become charged by tunneling of electrons or holes from the silicon substrate through a tunnel oxide. Successful operation requires that the charge does not leak away by the assistance of traps or defects in the material stack or by thermally-assisted tunneling to the substrate.…”