Abstract

This seminar describes the development and implementation of a cryogenic on-chip multiplexer which significantly increases the number of quantum devices measured on a single chip. It is demonstrated to contact an array of 256 (16×16) split-gate transistors, where each device is individually measureable, using only 19 electrical contacts. Split-gate transistors form one-dimensional channels in a two-dimensional electron gas (2DEG) formed in a GaAs/AlGaAs heterostructure. The implementation of the multiplexer does not require the modification of existing fabrication or experimental set-ups. The compatibility of the multiplexer with existing apparatus allows for easy integration into current research. This provides a major multiplication in the effectiveness of research. This enables new experiments to study yield, reproducibility and statistics of electrical properties.

The yield, reproducibility, spatial variations and statistical analyses of particular electrical characteristics which exist in split-gate transistors are presented. These studies are important in the area of quantum electronics. At low temperatures, split gates exhibit quantisation of conductance in units of 2e2/h. A ‘quantum yield’ (based on the behaviour of the device) was defined which increases from 55% to 86% when illuminating the split-gate devices with a light emitting diode (LED). Correlations and spatial variations of electrical properties are investigated upon illumination and a second cooldown. Techniques to quantify the variation in electrical properties, due to short-scale variations in electron density (which limit reproducibility from device-to-device), of the wafer are presented.