Broadband visible-to-telecom wavelength germanium quantum dot photodetectors

Germanium (Ge) quantum dot (QD) photodetectors (PDs) were fabricated on Ge substrates exhibiting a broadband, visible to near-infrared (near-IR) photoresponse in the λ = 400–1550 nm range. Room-temperature responsivities (Rsp) up to 1.12 A/W and internal quantum efficiency IQE = 313% were obtained, superior to conventional silicon and germanium photodiodes. Noise analysis was performed at visible λ = 640 nm and telecom λ = 1550 nm wavelengths, both yielding room-temperature specific detectivity D* ≃ 2 × 1010 cm Hz1/2 W−1. Lowering the operating temperature and incident power led to sharply enhanced performance, with D* = 1.1 × 1012 cm Hz1/2 W−1 and IQE = 1000% at T = 100 K for an incident power of 10 nW at λ = 1550 nm. Based on their simple fabrication and silicon technology compatibility, these Ge QD PDs represent a promising alternative for broadband, high-performance visible to near-IR detection.