Investigations on transient regime of Ge2Sb2Te5-based vertical photodetector integrated with silicon-on-insulator waveguide

In this study, we conducted finite difference time domain simulation investigations of the transient responses of silicon-on-insulator waveguide-based vertical photodetectors using the phase-change material Ge2Sb2Te5 (GST) as a sensing element on the Si core. The charge transport characteristics comprising the carrier and displacement current were comprehensively studied based on variations in the dimension, pulse width, and frequency by solving the drift-diffusion model under constant biased conditions. The dynamic behaviors of two stable GST phases comprising amorphous (aGST) and crystalline (cGST) were compared in terms of the peak amplitude, peak arrival time, and rate of change in the current for both phases. The cGST based device was much faster, with the lowest peak arrival time of 21.5 ps and rate of arrival of 56.5 mu A/ps at a wavelength of 1150 nm. The lowest value peak arrival time was 22 ps with a slope of 4 mu A/ps for the aGST based device at a wavelength of 1850 nm. The results showed that cGST is suitable for lower wavelengths whereas aGST is appropriate for higher wavelengths in the near-infrared operating range to obtain instant dynamic response, thereby allowing the production of a tunable photodetector with a phase-change material.