Fig. 1. Schematic illustration of the PC measurements. When the excitation laser is resonant with the transition energy, an exciton is created and measured as a PC signal.

Fig. 2. (a) Macro-PL spectrum of our QD. The emission range extends over 1.3 µm. (b) PC spectra of a single QD in the region of the excitonic ground state energy. The background has been subtracted. In this CW-experiment, the laser energy is fixed for each spectrum, whereas the transition energy is tuned by gate voltage via the QCSE. A number of different laser energies have been recorded sequentially, each leading to a resonance at a specific voltage on the photodiode. With increasing gate voltage, the resonant PC intensity increases due to a faster tunneling rate.

Fig. 3. Optical setup for pulse-excited PC measurements. Spectral pulse shapes of input and output from/to the Pr-doped fluoride fiber amplifier are shown in insets. The output pulse is amplified by approximately 14 dB. No spectral broadening is observed in the amplification process. Temporal pulsewidth of the output pulse is 7 ps which is close to the Fourier-transform limit.

Fig. 4. Power dependence of the PC intensity. (a) Rabi oscillation of the PC at resonance for increasing excitation pulse area. The photocurrents are obtained for different accumulation times to obtain sufficient S/N ratio. The oscillation is fitted by an exponentially-damped sine function (red line). The green dashed line shows the theoretical maximum of the PC. A value of pulse area of 1 corresponds to an average CW excitation intensity of ~250 µW on the QD sample. (b) I-V properties at excitation of π/2 and π pulses centered at 1300.55 nm. The upper axis shows the energy shift of the exciton energy from the central wavelength of the excitation pulse converted from the gate voltage via the QCSE.