Figure 1

(a) Schematic of the device structure. (b) Scanning electron microscope image of a cross-wire structure with an active area of about $1\mu {\mathrm{m}}^2$. The top wire forms a bridge between a contact pad (not shown) and the bottom wire, using an air gap for isolation. (c) Schematic band diagram of structure under forward bias, close to resonance. Capture of a single photoexcited hole by a quantum dot lowers the potential of the dot and alters the resonant tunneling condition (red dashed line).Reuse & Permissions

Figure 2

(a) Current-voltage characteristic of a $10\mu \mathrm{m}\times 10\mu \mathrm{m}$ mesa device with 10 nm ${\mathrm{A}\mathrm{l}}_{0.33}{\mathrm{G}\mathrm{a}}_{0.67}\mathrm{A}\mathrm{s}$ barriers at 4 K, measured with $100\mathrm{n}\mathrm{W}{\mathrm{c}\mathrm{m}}^{-2}$ (dashed line) and without (solid line) illumination. Illumination causes the forward bias tunneling resonance to shift to lower bias due to the capture of photo-excited holes in the dots. (b) Forward bias tunnel resonance for illumination intensities from 1 to $100\mathrm{n}\mathrm{W}{\mathrm{c}\mathrm{m}}^{-2}$ for a $1\mu {\mathrm{m}}^2$ cross-wire device (arrow shows bias used for single-photon detection).Reuse & Permissions

Figure 3

(a) Time-resolved measurements of a cross-wire device with 10 nm ${\mathrm{A}\mathrm{l}}_{0.33}{\mathrm{G}\mathrm{a}}_{0.67}\mathrm{A}\mathrm{s}$ barriers at 5 K: (i) under constant illumination with a red LED of about 0.2 photons per second per $\mu {\mathrm{m}}^2$; (ii) after illumination has been switched off. (b) Rate of upwards steps counted with $1\mathrm{p}\mathrm{A}{\mathrm{s}}^{-1}$ discriminator level versus rate of incident photons from a 550 nm source on the active device area in a cross-wire device. Best fit (red line) giving a quantum efficiency of 10.9% for this particular discriminator level. (c) Quantum efficiency (solid line) and dark count rate (dotted line) versus step-counting discriminator level of a cross-wire device using 550 nm light. (d) Quantum efficiency as a function of wavelength of a cross-wire device with 310 nm intrinsic GaAs absorbing layer. Calculated fraction of incident light absorbed in intrinsic GaAs layer (solid curve) and calculated absorption within bottom 150 nm of intrinsic GaAs layer (red dashed curve).Reuse & Permissions

Figure 4

(a) Time-resolved measurements of a cross-wire device with 3 nm ${\mathrm{A}\mathrm{l}}_{0.33}{\mathrm{G}\mathrm{a}}_{0.67}\mathrm{A}\mathrm{s}$ barriers at 4 K. Lower portion: output of current amplifier showing a photon induced step (rise time is limited by the bandwidth of the dc amplifier). Upper portion: output of high-bandwidth differentiating electronics. (b) Count rate of photon induced pulses under illumination and in the dark as a function of discriminator level using a pulse-counter gate time of 200 ns. (c) Temporal response of the device in response to $<1$ photon laser pulses.Reuse & Permissions