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Title: Experimental studies on a planar unipolar nano-diode
Author: Zhang, Linqing
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2014
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This research focuses on a solid-state planar unipolar nano-diode, known as a self-switching diode (SSD). The planar architecture of the SSD ensures the parasitic capacitance of this device much smaller than that of a vertical diode of comparable size, allowing a high working speed. SSDs have been successfully demonstrated as terahertz detectors operating up to 1.5 THz on a GaAs/AlGaAs two-dimensional electron gas (2DEG) wafer at room temperature and up to 2.5 THz on an InGaAs/InP 2DEG wafer at 150 K. To date, SSDs fabricated using GaAs and InGaAs have been extensively studied. The primary aim of this research is to explore SSDs on other promising materials such as InAs/AlSb because of its high electron mobility and GaN/AlGaN for potential high-power applications. First, InAs/AlSb-based SSDs were explored. The fast forming of native oxide of the AlSb layer presented a major challenge. This was effectively dealt with by the addition of 10% Gallium to the AlSb layer and a further coating of polymethyl methacrylate on the devices immediately after etching. Both DC and RF measurements were subsequently carried out to provide a proof of principle. The SSDs were found to have higher current at room temperature than those produced on GaAs and InGaAs 2DEG wafers. This was, to our knowledge, the first nanoelectronic device that was demonstrated using InAs/AlSb by wet etching. Noise performance of the SSD is crucial when it is used as a microwave or terahertz detector since low-frequency modulation is often used during detection. A noise characterisation setup based on a two-channel cross-correlation principle was developed, which is capable for SSDs with a wide range of impedance values. The noise setup was first used to characterise GaN/AlGaN-based SSDs. The effect of SSD design on the low-frequency noise was investigated. Results indicated that the measured low-frequency noise at various bias currents was dominated by flicker noise and described by Hooge's formula. The Hooge's constant was determined. We show that arranging a number of SSDs in parallel into an array effectively reduced the low-frequency noise and resulted in a lower corner frequency. Finally, the effect of filling a high-k dielectric material into the SSD nanotrenches was studied experimentally for the first time. A 100 nm thick, high-k SiNx film was applied using plasma-enhanced chemical vapour deposition. DC, RF and noise measurements were performed. The results demonstrated improved I-V characteristic, higher RF responsitivity and reduced low-frequency noise.
Supervisor: Song, Aimin Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: heterostructure ; terahertz ; high-k dielectric ; self-switching diode ; nano-diode ; noise