Growth-Microstructure-Device Performance Correlations for III-nitride Optoelectronic and Power Devices on Sapphire and Silicon

The talk will describe the defect-to-device performance correlations for optoelectronic and power devices on hetero-epitaxially grown III-nitride epi-layers on silicon and sapphire. While UV detectors and power electronic devices might seem far apart, we see similarities between the defect origins of dark current in the former and leakage currents in the latter. Both have their origins in crystal growth. The first part of the work focuses on the correlation between performance parameters of vertical deep-ultraviolet photodetectors on c-plane sapphire and the density of extended defects vis-a-vis screw and edge dislocations. Through a careful optimization of nucleation density on the growth surface, state-of-the-art crystalline quality AlN epi-layers were grown. This led to the realization of record performance 289 nm p-i-n photodiodes with zero-bias quantum efficiency of 92 %, leakage current below 1 nA at 100 V and breakdown field in excess of 6 MV/cm. Performance of III-nitride power devices on silicon, on the other hand, was found to be more sensitive to structural defects such as surface pits as compared to dislocations. By utilizing a two-temperature growth technique which involved an AlN layer grown at high temperatures, a significant reduction in the pit density could be achieved. This resulted in three-orders of magnitude reduction in lateral as well as vertical leakage in AlGaN/GaN high electron mobility transistors (HEMTs) on silicon. To achieve a further reduction in the reverse leakage current and an enhancement in the device breakdown voltage, point defect control also becomes important. Carbon doping to reduce the background n-carrier concentration in the GaN epilayers is discussed as one of the possible approaches. Reduction of pit density and C-incorporation cumulatively led to the realization of 2 MV/cm vertical breakdown field in AlGaN/GaN HEMTs on silicon.