The application of GHz bandwidth electrical pulses to a single semiconductor quantum dot.

Abstract

Quantum dots contain several isolated two-level quantum systems, an ideal starting point for the creation of a qubit. A single quantum dot embedded within a chargetunable heterostructure can be optically isolated using confocal microscopy, and electrically manipulated using an applied voltage. This thesis presents progress towards full opto-electrical control over a single dot, with a specific interest in the creation of a fully controllable electrically triggered deterministic single photon source. Polarisation control was incorporated into the confocal microscope setup, and polarisation filtering was used to enhance the signal to noise ratio in photoluminescence studies. Weierstrass solid immersion lens technology was included in the microscope design in order to improve the collection efficiency of dot photoluminescence. Static voltages were applied over single dots. Time-resolved spectroscopy allows the identification of hole tunnelling from the dot to the capping layer-superlattice interface. Suppression of hole tunnelling is achieved by altering the wafer structure. Autocorrelation measurements exhibit a finite second-order correlation at zero time delay, which is attributed to hole recapture from the wetting layer. Resonant excitation of the neutral exciton results in the creation of a negative trion in a specific voltage regime. Photolithography and electron-beam evaporation were used to manufacture several micron-scale opto-electronic devices. Several changes were made with the intention of reducing the resistance and capacitance of the device, with respect to the original macroscopic design. Photoluminescence measurements show that single dots in the new devices are capable of responding to GHz bandwidth voltage pulses. Finally, GHz bandwidth voltage pulses were applied to several single quantum dots. Single and multiple electron charging was observed on the timescale of exciton recombination. Several memory bit variations were demonstrated, each with an electrically triggered read-out mechanism. Two electrically triggered deterministic single photon sources were demonstrated, one using CW non-resonant optical excitation, the other using pulsed resonant optical excitation. Lastly, rapid adiabatic passage was attempted, with mixed results.