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Title: Gallium nitride sensor devices fabrication techniques and characterisation
Author: Schuller, Timothy Adam
ISNI:       0000 0004 2718 3038
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2011
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A saccharide sensor was fabricated using an AlGaN/GaN heterostructure structure and a boronic-acid containing receptor. Parallel to this, photoelectrochemical (PEC) etching of Gallium Nitride (GaN) was employed both as a nanostructuring technique and as a method of rapid dislocation density enumeration. The device fabrication techniques necessary for the development of devices based on n-type GaN and its alloys were successfully implemented. A robust photolithographic mask capable of producing a variety of transistor and sensor structures was designed and fabricated. Surface Charge Lithography (SCL) was studied and implemented as a technique for the nanostructuring of n-type GaN. In contrast to previous work (where patterns with feature sizes down to 100nm were created¹), several shortcomings of the technique were noted and subsequently investigated: a failure to achieve the intended minimum feature size; elongation of features in the direction of FIB instrument rastering; and the loss of thin features perpendicular to the rastering direction. A pattern design scheme to overcome these shortcomings was proposed along with experimental improvements expected to alleviate such issues. A novel receptor molecule employing a phenylboronic acid (BAT) was synthesised and used to functionalise an AlGaN/GaN FET device, thereby creating an electronic saccharide sensor device. The response of the sensor to a panel of saccharides (fructose, galactose and glucose) was investigated, with the order of response confirming previous findings (decreasing from fructose to galactose to glucose). The device was found to have good stability prior to failure, indicating that this type of sensor device shows a great deal of potential for wider use. PEC etching was used as a technique for determining the dislocation density in two distinct GaN on sapphire structures with thick AlN buffer layers. The SRI sample (100nm of GaN with 500nm of AlN) had a dislocation density of 1.9±O.2xl0⁹cm-², while the SH2 sample (500nm of GaN with lOOnm of AIN) had approximately twice this density, at 3.8±O.2xl0⁹cm-². The differences are thought to primarily arise from the difference in AlN thickness.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available