(Color online) Schematic view of the GHz bandwidth device. (a) The layer structure with the active region of quantum dots embedded between the tunnel barrier to the highly n-doped back contact and the capping layer. On top of the capping layer, the AlAs/GaAs superlattice prevents current flow to the 5-nm-thick NiCr, micron-sized Schottky gate. The ohmic contact between the back contact and the surface is made by annealing AuGe/Ni/AuGe layers. (b) Top view of the device, showing the 50-Ω coplanar waveguide structure, the 400-nm deep etch, and the contact strip for the miniaturized Schottky gate.
(Color online) The X 1- voltage plateau under cw non-resonant optical excitation as a probe of the response time of the device. (a) The PL for a range of V g for a single dot illuminated with 270 nWμm−2 of 830 nm cw laser light. The scale depends linearly on the counts (the readout signal from the CCD camera), starting from white (less than 300 counts) with increasing intensity to red ≅10 000 counts. The exciton responsible for each PL line is identified. V L = −10 mV and V H = 160 mV (dotted lines) are voltage points chosen to be 20 mV beyond either edge of the X 1- voltage plateau. (b) An oscilloscope trace of the output of the PPG, showing a 10-MHz repetition rate square-wave voltage pulse applied to the device between V L and V H as a function of time. (c) TCSPC measurements of X 0 (black dotted line), X 1- (red solid line), and X 2- (blue dashed line) with the square wave applied to the device.
(Color online) The signal truncation of a voltage pulse applied to the quantum-dot device. (a) PL against V g , for the same dot as Fig. 2(a), but now shown for a smaller range. (b) An oscilloscope trace of the 20 MHz repetition rate voltage pulse applied to the device between V L and V H as a function of time. The voltage difference between V L and V H is kept constant at 200 mV. The voltage offset ((1/2)(V L + V H )) and the pulse duration (ΔT) were varied, indicated by the arrows in (a) and (b). (c) The X 1- PL against voltage offset for the dot from (a), with a time-varying applied voltage as in (b), for ΔT = 10 ns. There are two PL lines as a result of emission from X 1- at different offset voltages. The voltage difference between the onset of each PL line is marked as ΔV. (d) The PL against voltage offset for the dot from (a), with a time-varying applied voltage as in (b) but with ΔT = 1 ns. (e) ΔV measured for various values of ΔT (black squares), alongside an exponential fit (ΔV = ΔV 0 (1− exp(−t/τ))) with an amplitude of ΔV 0 = 200 mV, and a 1/e rise time of τ = 1 ns. All data shown were taken with 270 nWμm−2 of 830 nm cw laser light.
(Color online) TCSPC of X 1- following resonant excitation of X 0. (a) PL against V g for a dot illuminated with 5.5 nWμm−2 of non-resonant 830-nm cw laser light. The exciton responsible for each PL line is identified. The region H marks the hybridization region, a voltage extent in which resonant excitation of X 0 results in emission of X 1- PL. (b) An oscilloscope trace of the 10-MHz repetition rate square wave, with 200-mV amplitude. (c) Spectra for the dot in (a) as a function of V g when the dot is illuminated with 73.4 μWμm−2 of laser light tuned to 1.3023 eV, resonant with the X 0 transition of the dot. PL emission from X 1- marks the voltage region H. (d) TCSPC of X 1-, for the dot from (a), illuminated with 73.4 μWμm−2 of light tuned to 1.3023 eV, with a time-varying applied voltage as in (b), with an offset of 175 mV. Two PL peaks are observed at 26 ns and 76 ns, and a maximum (A) and half maximum (B) point on each peak are identified. (e) The time of occurrence of peak A as a function of the voltage offset ((1/2)(V L + V H )) with the applied pulse from (b). (f) The time of occurrence of B as a function of the voltage offset with the applied pulse from (b). (e), and (f) show exponential fits to the rise/fall.
Article metrics loading...
Full text loading...