|Jha, Shrawan Kumar
|AlGaN/GaN based HEMT structures and applications
|Hong Kong Polytechnic University -- Dissertations.
Modulation-doped field-effect transistors.
|Department of Electronic and Information Engineering
|xxi, 211 leaves : ill. ; 30 cm.
|GaN based technologies are capable of addressing the emerging technological demands arising from the current needs of rapidly changing electronics markets. AlGaN/GaN heterostructures are promising candidates for a number of applications. Reliability and performance enhancement remains the biggest challenges in the commercialization of GaN based technologies. In this work, both of these issues were addressed in context of the devices incorporating, single and double AlGaN/GaN heterostructures. In addition, novel application of these heterostructures as HEMT based biosensor device was demonstrated. Implementation of gate recess in field effect devices has been touted as an effective means for improving the transconductance of the transistors. Potential influence of this recess technology on the low-frequency noise characteristics of the HEMT devices was investigated. It was found that the magnitude of noise is strongly dependent on the recess depth. Degradation of excess noise, in unrecessed and recessed gate HEMTs, due to hot-electron stressing was also studied. It was observed that noise degradation can be identified to occur in two distinct phases. In the first phase, devices initially show fluctuations in the noise properties around a constant average value. This was shown to arise from the modulation of the percolation paths of the carriers in the two-dimensional electron gas. In the second phase, irreversible degradation of noise power was observed due to generation of interface states at the AlGaN/GaN heterointerface. The two phase degradation was observed for all the recessed and unrecessed devices, however, it was found that recessing significantly affects the device life time. Low-frequency noise in MOCVD-grown AlGaN/GaN/AlGaN/GaN double channel HEMTs was investigated over a wide range of temperatures. Bias dependence of noise properties was studied. Generation-recombination noise was observed to be arising from the traps with activation energies 140 meV, 188 meV and 201 meV. Hooge parameter was estimated to be 1.64 x 10-3 at room temperature. Experimental results of the noise measurements on TLM structures reflected insignificant contribution of contact noise in studied structures. A novel application of GaN based heterostructures for bio-sensing was demonstrated. Feasibility of using AlGaN/GaN heterostructures for cell culture was studied. High density cell monolayers of human osteoblast-like cells could be achieved after surface functionalization. Effect of drug-H7, and trypsin was optically inspected. Large area gateless HEMT like devices were fabricated and cell monolayers were grown over the gate area. Effect of trypsin on these cells was electrically monitored with this device. Detection is based on current modulation in the device due to removal of the cells from the gate area. The time scale recorded from optical inspection and electrical inspection were found to be the same. This suggested the feasibility of using the proposed HEMT-based biosensor devices for a wide variety of biosensing applications.
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