Gallium nitride based heterostructure growth and application to electronic devices and gas sensors

This thesis focuses on III-Nitrides for electronic and gas sensing devices. Systematic material growth optimization was performed by using various characterization techniques in order to improve device performance.;For high frequency device operation, resistive bulk GaN is preferable to prevent parasitic leakage through the layer. Growth conditions for bulk GaN were optimized for this purpose using an in-house Metal Organic Vapor Phase Epitaxy system. The pinch-off current of AlGaN/GaN Heterostructure Field Effect Transistors based on these layers was reduced by a factor of twenty in comparison with devices fabricated with non-optimized bulk GaN. The best results obtained from this heterostructure were a room temperature Hall mobility and sheet charge density of about 1270 cm2/Vs and 7.0·1012 cm-2, respectively.;AlN/GaN HFETs were investigated because of the possibility of reducing gate leakage current, operating at higher temperature and higher power in comparison with AlGaN/GaN HFETs. In-situ SiN x was employed for surface passivation. SiNx improved the ohmic quality of this device and the RF characteristics were also improved; fT and fmax were enhanced by a factor of two and three, respectively in contrast to devices without the passivation.;To address the issue pertaining to the polarization fields of c-plane GaN, non-polar GaN growth was investigated using r-plane sapphire substrates. The RMS surface roughness and full width at half maximum were improved to 2 nm and 1000", respectively, using high temperature AlN buffer layers. This shows a quality improvement by a factor of two to three compared to layers grown using low temperature GaN NLs in this work.;Diodes were fabricated for gas sensing using c-plane GaN and AlGaN/GaN heterostructures. Optimization of size and thickness of the Pt Schottky contact improved CO sensitivity by a factor of six compared to non-optimized sensors. Fabry-Perot filters with GaN/air gap based distributed Bragg reflectors were designed at 450 nm as a detector in optical gas sensing systems. Simulations of their optical and mechanical properties showed the feasibility of this device design. The growth and etching study of AlN as a sacrificial layer manifested that reasonable etching rate can be obtained when the layer was grown at around 800°C.