Investigation of Point Defects in AlGaN/GaN High Electron Mobility Transistor Heterostructures Grown on Si Wafers
Type of DegreeDissertation
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This PhD dissertation focuses on the investigation of surface/interface defects in AlGaN/GaN high electron mobility transistors (HEMTs) on Si wafers for power electronic applications. Recently, significant attention has been paid to gallium nitride (GaN) for application in power electronics due to its desired materials characteristics. Among the power electronic devices based on GaN and its alloys, AlGaN/GaN high electron mobility transistors (HEMTs) are considered promising. Nevertheless, deleterious effects of high concentration of point defects on the performance of AlGaN/GaN high electron mobility transistors (HEMTs) cannot be disregarded. It is of great importance to analyze deep level defects in the AlGaN/GaN HEMTs structure since it is recognized that deep level defects are the main source for causing current collapse phenomena leading to reduced device reliability. Raman spectroscopy, photoluminescence (PL), and spectroscopic photo current-voltage measurements were performed to characterize point defects at surface/interface and bulk in AlGaN/GaN HEMTs wafer. Recently, a simple and novel spectroscopic photo I–V method of diagnosing the homogeneity of electrically-active defect distribution in the large area AlGaN/GaN HEMTs epi-structure grown on 6-inch silicon wafers has been developed. The spectroscopic photo current-voltage (I-V) measurements with subbandgap illumination exhibited the presence of sub-bandgap defects with different activation energies for each sample. The depth-resolved ultra-violet (UV) spectroscopic photo current-voltage (I-V) (DR-UVSPIV) measurements revealed that the depth dependent distribution of the defects for these samples aredifferent. Time resolved photocurrent spectroscopy (TRPC) was used to distinguish between the traps that have the same de-trapping energy but have the different physical origins. It was demonstrated that even though electrically active defects for two devices on the same pieces of AlGaN/GaN HEMTs heterostructures cannot be distinguished in Raman spectroscopy and PL measurements, they can be differentiated by using the spectroscopic photo I-V with sub-bandgap illumination and DR-UV-SPIV measurements.