Novel Group-IV Alloy-Based MOS Field-Effect Phototransistors for Near-Infrared Applications

This work describes the novel
${\text {Si}}_{{1}-{x}}{\text {Sn}}_{x}$
alloy-based n-metal-oxide-semiconductor phototransistors (nMOSPTs) grown on silicon (Si) substrate via
${\text {Si}}_{{1}-{x}}{\text {Sn}}_{x}\,\,{(} {x}={3}.{6}\% {)}$
virtual substrate (VS) for near-infrared (NIR) applications. The concept of transferring high-speed optical signals directly to the complementary metal-oxide-semiconductor (CMOS) photodetector paves the way for novel applications of light to aid electrical functions. As a channel material, SiSn is used in the proposed device’s structure. For the purpose of fabricating CMOS devices, the key benefit of using SiSn as a channel material is that it is inexpensive and compatible with Si substrates. In this study, SiSn with 3.6% Sn is introduced as a VS to minimize the lattice mismatch between the Si substrate and
${\text {Si}}_{{1}-{x}}{\text {Sn}}_{x}$
with
${x}={5}\%-{24}\%$
active layer. The bandgap shrinks as Sn is incorporated into Si, which results in a wavelength redshift. As a result, the photodetection range shifts toward a longer wavelength. Moreover, the Sn alloying results in a high absorption coefficient, which increases the responsivity of the device. The designed device is simulated using a commercially available multiphysics tool. The proposed device with a 1000-nm channel length, shows the responsivity and bandwidth of 15.8 A/W and 4.8 GHz, respectively, at
$\lambda $
= 850 nm with
${V}_{\text {GS}}={V}_{\text {DS}}={1}\text {V}$
for
${x}={5}\%$
. By increasing the Sn concentration to 24% and gate and drain voltages to 4 V, the proposed device achieves the responsivity and bandwidth of 2260 A/W and 61.7 GHz, respectively. Furthermore, it is expected that miniaturization would enhance future devices’ responsivity and bandwidth.