Aluminum gallium nitride/gallium nitride based HEMT structures and applications

In this work, reliability and noise properties of GaN based HEMTs were addressed in context of devices incorporating either a single or a double AlGaN/GaN heterostructure. In addition, novel application of AlGaN/GaN heterostructures in HEMT based biosensor device was demonstrated.Influence of creating gate recess by RIE technique on the low-frequency noise characteristics of the HEMT devices was investigated. Magnitude of noise was found to be strongly dependent on the recess depth. Degradation of excess noise in unrecessed and recessed gate HEMTs due to hot-electron stressing was studied. Noise degradation was 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.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. Traps with activation energies 140 meV, 188 meV and 201 meV were identified. Experimental results of the noise measurements on TLM structures reflected insignificant contribution of contact noise in studied structures. Hooge parameter was estimated to be 1.64 x 10 -3 at room temperature. This value is similar to the values reported in literature for single channel HEMTs and hence, double channel devices offer reasonable dc and noise properties.A novel application of GaN based heterostructures for bio-sensing was demonstrated. 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. Event time scale recorded from optical inspection and electrical inspection were found to be the same, indicating the feasibility of using GaN HEMT-based structures for biosensing.