Thermal and electrical studies of gallium nitride-based heterojunction field effect transistors and light emitting diodes

Thermal modeling and measurements of AlGaN/GaN heterojuction field effect transistors (HFETs) built on sapphire and SiC substrates, and InGaN/GaN multi-quantum well (MQW) structure light emitting diodes (LEDs) on sapphire are studied. In thermal modeling, PAMICE and UNITHERM code are used to calculate temperatures in a 3-D model. In thermal measurement, nematic liquid crystal thermography (NLCT) is employed to determine the junction temperature of HFETs device built on sapphire and SiC substrates. Temperature measurements give the actual junction temperature Tj while the thermal modeling confirms the measurement results. The temperature of the active region is the junction temperature and it is the junction temperature that directly affects the device performance parameters. Therefore, Tj is an important parameter for studying and understanding the GaN-based semiconductor devices characteristics.; A new nematic liquid crystal thermography configuration with a color filter using infrared (IR) laser illumination source has been developed to measure the junction temperature Tj of light emitting devices. The junction temperature Tj of InGaN/GaN multi quantum well (MQW) light emitting diodes (LEDs) are measured with a new nematic liquid crystal thermography method. The new configuration is clearly different from conventional nematic liquid crystal thermography method.; With junction temperature Tj information available, the physical model of the light emitting diodes (LEDs) with the current spreading layer is studied. The physical model can be a useful tool for optimizing the conversion efficiency of the LEDs with the current spreading layer. For LEDs with the quantum-well (QW) structure, the use of the ideal diode equation is fundamentally incorrect. A new diode model is studied for LEDs with QW structure. Temperature measurements and a device model of the LEDs further enables one to predict and assess possible performance improvement during the modification of device structures and packages. Temperature measurement and a device model are valuable for improving LEDs device structures, packages, and helps the physical understanding of the device.