Selenium-assisted surface enhancement single-crystal PbSe/Ge heterojunctions for a high detectivity uncooled mid infrared wavelength photovoltaic detector

Abstract

The development of uncooled mid-infrared detectors has been constrained by the epitaxial incompatibility between IV–VI semiconductors and silicon-based read-out integrated circuits (Si-ROICs). To overcome this limitation, a surface selenization strategy is developed, enabling the epitaxial growth of single-crystalline PbSe on Ge substrates and the realization of functional PbSe/Ge heterojunction photovoltaic detectors. The Se-treated Ge surface is found to form a Se-terminated atomic layer, which significantly enhances the nucleation density and promotes two-dimensional coalescence into epitaxial films. The fabricated heterojunction detectors exhibit peak specific detectivities of 4.0 × 10⁹ cm Hz^1/2 W⁻¹ at 300 K and 1.8 × 10¹⁰ cm Hz^1/2 W⁻¹ at 180 K under blackbody illumination, achieving performance comparable to state-of-the-art uncooled mid-infrared devices. Meanwhile, the theoretically optimized n–i–p structure PbSe/Ge photodetector suggests further detectivity enhancements to 4.0 × 10¹⁰ cm Hz^1/2 W⁻¹. This surface modification strategy provides a viable pathway for monolithic integration of high-performance PbSe photodetectors with silicon readout circuitry, representing a significant advancement toward CMOS-compatible mid-infrared imaging systems.