Ge0.95Sn0.05 on Si avalanche photodiode with Spectral Response Cutoff at 2.14 micrometer

TL;DR

This paper demonstrates a GeSn-based avalanche photodiode with a spectral cutoff beyond 2.1 μm, utilizing a SACM structure and a Ge buffer to improve material quality and achieve SWIR detection at room temperature.

Contribution

It introduces a GeSn APD with a SACM structure and Ge buffer layer, enabling long-wavelength SWIR detection with notable responsivity and gain at various temperatures.

Findings

Spectral cutoff beyond 2.1 μm at room temperature

Responsivity of 0.55 A/W at 1.55 μm

Maximum gain of 3.44 at 77 K

Abstract

GeSn-based avalanche photodiode (APD) operating in shortwave infrared (SWIR) wavelength was demonstrated in this work. A separate absorption and charge multiplication (SACM) structure was employed to take advantage of long wavelength absorption in GeSn and low impact ionization ratio of Si. Due to lattice mismatch between Si and GeSn that would degrade GeSn material quality if with direct growth, a 240-nm-thick Ge buffer was utilized which simultaneously allows for the transporting photo generated electrons from GeSn absorber to Si multiplication layer. Spectral response showed the cut off wavelength beyond 2.1 {\mu}m at room temperature. Dart current and capacitance-voltage measurements indicated a punch-through voltage of -10 V. The measured responsivities were 0.55 A/W and 0.34 A/W under 1.55 {\mu}m and 1.9 {\mu}m excitation lasers, respectively. The maximum gain was obtained as 3.44 at 77 K under 1.9 {\mu}m laser. Even at 250 K, the calculated gain was greater than unity. Simulation of electric field distribution revealed that the GeSn is partially depleted at operating voltages, which can be improved by reducing the background doping levels in GeSn absorber and Ge buffer layer.