Fabrication of a Strained-Silicon/Sapphire Heterostructure-Based Broadband Photodetector

Strained silicon shows enormous potential in photoelectric detection with an adjustable band structure and carrier dynamics. Herein, crystalline silicon with controllable strain is fabricated on a sapphire wafer by ultrafast laser-induced backward transfer. Upon intense ultrafast laser ablation, amorphous SiO_x can be formed between deposited silicon and sapphire substrate, in which tensile strain in silicon is generated to coordinate the lattice mismatch and the difference of thermal expansion coefficients at the heterojunction. The change in tensile strain from 0.27% to 0.05% can be achieved by adjusting the thickness of the deposited silicon layer. A maximal photocurrent (0.97 μA) arises on the silicon photodetector with 0.15% strain under near-infrared illumination (1030 nm wavelength, 2 W cm^-2 intensity) at a fixed source-drain bias (V_ds) of 1 V. With the optimal band structure modification, it can further exhibit broadband photoresponse ranging from 532 to 1030 nm, achieving a high responsivity of 0.27 A W^-1 at V_ds = 1 V and a specific detectivity of 4.6 × 10¹⁰ Jones. In addition, SiO_x passivation, which suppresses the midgap trap density, can lead to a low dark current below 18 nA at V_ds = 5 V. Such a controllable strain regulation method, therefore, provides an alternative approach for fabricating a high-performance semiconductor-on-sapphire heterogeneous structure.