Thesis Dissertation Defense

This dissertation presents three elements of a project to investigate development of a novel solid state particle detector. The detector design incorporates Schottky-diode-connected HEMTs formed of gallium nitride (GaN) layered with aluminum gallium nitride (AlGaN); GaN/AlGaN is an ultra-wide bandgap semiconductor that is also piezoelectric. We hypothesize that particle interactions in the detector cause local and impermanent variations in polarization at the metal-semiconductor interface in the Schottky diode, which can be observed as transient signals at the circuit output. This detector design is based on the bandgap reference circuit, an analog circuit whose output is stable under varying temperature, supply variation, and loading conditions. The circuit design achieves this stability by incorporating two circuit elements whose temperature dependencies have equal but opposite coefficients. We describe the development of this circuit design and present simulation and experimental temperature data that demonstrate improved stability over semiconductor device temperature dependence. To investigate this design, we fabricated two prototypes with discrete components and irradiated them. The first prototype was irradiated at Sandia National Laboratories, where transient signals were observed under alpha and neutron irradiation. The second prototype was irradiated at the Radiological Sciences and Engineering Laboratory in the Boggs Building at Georgia Tech. Analysis of this set of data from the Georgia Tech experiments provides evidence from changes in the frequency spectrum and high values of cross-correlation between trials that alpha particles were observed. However, data from the neutron does not show the same magnitude of changes, so we believe additional filtering and experimentation are required to provide stronger evidence of neutron observation. Finally, we began simulations in Geant4 to start testing the physical mechanism hypothesis; a roadmap of future work is discussed to serve as a guide for future researchers. Ideas for future work regarding circuit simulation, experimental changes, and Geant4 simulation will be shared. In conclusion, this dissertation presents circuit development, irradiation experimentation, and preliminary simulations towards the development of a novel solid state semiconductor detector that utilizes ultra-wide bandgap materials for particle detection.