High-performance germanium quantum dot photodetectors in the visible and near infrared

Abstract We present our work on high performance germanium (Ge) quantum dot (QD) photodetectors (PDs), fabricated on Si and Ge substrates, that operate via tunneling transport through a QD-containing active layer and feature high internal photoconductive gain. In the λ = 400–1100 nm range, the PDs fabricated on Si substrates exhibit room-temperature spectral responsivity ( R sp ) up to 4 A/W and internal quantum efficiency (IQE) up to 700%. At λ = 640 nm and 12 μ W of incident power, signal-to-noise ratio (SNR) of 7 × 10 6 and specific detectivity ( D * ) of 1.2×10 11 cmHz 1/2 W −1 are obtained. The PDs demonstrate 3 dB bandwidths ( f 3 dB ) up to 10 MHz, corresponding to response times of ∼ 40 ns. When operated at 100 K temperature the performance improves, especially at low incident power, where at 10 nW D * increases to 2 × 10 13  cmHz 1/2 W −1 , due to IQE in excess of 22000%. In order to extend the photoresponse into the near-infrared (near-IR), PDs were fabricated on Ge substrates, yielding room-temperature R sp = 1.5 A/W, IQE = 134% and f 3 dB = 10 kHz at the λ = 1550 nm telecommunication wavelength. Significant improvement to f 3 dB is expected in PDs employing thinner QD-containing layers. Lowering temperature to 50 K and incident power to 10 nW yield D * = 10 13 cmHz 1/2 W −1 , resulting from IQE exceeding 60000%. Based on the above figures of merit, as well as their Si technology compatibility, our Ge QD PDs appear promising for high-performance photodetectors working in the visible and near-IR.