Few-photon Detection of Ge Quantum-dot Single-hole Transistors in Few-hole Regime under Visible Irradiation

Abstract

Abstract We reported few-photon detection and exciton binding-energy determination using tunneling-current spectroscopy of Ge-quantum dot (QD) single-hole transistors (SHTs) operating in the few-hole regime under 400 nm–1550 nm illumination. When the photon energy is smaller than the bandgap energy (1.46 eV) of the 20 nm Ge QD (for instance, under 1310 nm and 1550 nm illuminations), the peak voltage of tunneling current peaks remain intact even irradiation power is as high as mW. In contrast, 850 nm illumination (i.e., the photon energy is equal to the bandgap energy of the Ge QD) induces a considerable shift in the first hole-tunneling current peak towards positive VG (VG 0.08 V at 25.8 nW and 0.15 V at 112 nW) and even creates new additional photocurrent peaks at more positive VG (VG 0.2 V) at W irradiation. The abovementioned experimental observations were further strengthened for Ge-QD SHTs illuminated by 405 nm lasers with much lower power. The observed newly-photogenerated current peaks are ascribed to the interactions between few photoexcitons and single-hole tunneling within the Ge QD.