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Title: Progress towards GaAs multiplexed single-electron pump arrays
Author: Yi, Teng
ISNI:       0000 0004 7968 5494
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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In this thesis we present progress towards making multiplexed GaAs single-electron pump arrays. The single-electron pump is a device for transferring an accurate integer number 'n' of electrons per cycle to generate precise current $I=nef$, where $f$ is the frequency of the periodic AC voltage applied and $e$ is the electron charge. Multiplexing electron pumps may also allow the pumps to be measured in parallel, increasing the output current and thereby enabling a higher accuracy reading. Firstly, a 4 x 32 multiplexed wide-channel electron pump array is studied and we observe a large rectified current (about 100 $\mu$A) instead of a pumping current (which would be 18 pA at 110 MHz). We designed several variations of single wide-channel electron pump devices and found out that the rectified current is from the wide-channel electron pump and not the multiplexer. We developed a model to qualitatively explain the origin of rectified current in the wide-channel electron pump devices and investigate the effects of changing the RF frequency and amplitude on the rectified current. Secondly, we characterise the transmission of RF voltage signals through the quantum multiplexer using an array of bar gates. We find that about 300 mV AC amplitude voltage can be transmitted to the bar gate device, which may be sufficiently large for an electron pump to operate. We also present the statistical study of multiplexed bar gate devices. We find that 0.1 μm wide bar gates are different from 0.2 μm wide bar gate or wider gates: more negative voltage is needed to pinch off 0.1 μm wide bar gates, because 0.1 μm is comparable with the 2DEG depth. We redesign the multiplexer structure and determine that the capacitance of the multiplexer is about 1.93 pF which will help the future multiplexed single-electron pump array design to give best RF power transmission. Thirdly, since gate insulators are required in the multiplexed electron pump design. We demonstrate electron pumping in a single-electron pump device in which the gates extend across the entire GaAs channel, and are insulated from the GaAs channel by a polyimide layer as required in the multiplexed design. We also study how design variations such as the pump gates design (quantum dot radius and tunnel barrier width), channel etch design and order of fabrication will affect the RF power required to observe clear quantised pumping. Based on the above results, we present our designs for full GaAs multiplexed electron pump arrays.
Supervisor: Smith, Charles Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Single electron pump ; Quantum multiplexer ; Pump arrays