Noise Analysis of Group IV Material-Based Heterojunction Phototransistor for Fiber-Optic Telecommunication Networks

This paper presents an analytical study of the noise behavior and spectral responsivity of Ge
_1-x
Sn
_x
alloy-based heterojunction phototransistors (HPTs) for different Sn compositions and base doping concentrations. The structure consists of n-Ge/p
⁺
- Ge
_1-x
Sn
_x
/n
^-
- Ge
_1-x
Sn
_x
layers pseudomorphically grown on Si substrate via Ge virtual substrate, compatible with complementary metal-oxide-semiconductor technology. The high absorption coefficient of the alloy in base significantly improves signal-to-noise ratio in the high-frequency region, leading to efficient photodetection in the C - and L-bands of fiber-optic telecommunication window. A comparison is made between the theoretical findings for GeSn HPTs and the available data for currently employed group III-V compound-based HPTs, to examine if GeSn-based HPT can be a good alternative.