Nitrides Seminar - Tanay Tak
Thursday, October 10, 2024, 12:00PM
Attend in person at ESB 1001!
Zoom option also available
https://ucsb.zoom.us/j/81282134999?pwd=vUnE11gLhTMLt3zHbXy53ebT2yiGen.1
Meeting ID: 812 8213 4999 Passcode: 295294
Tanay Tak
Graduate Student Researcher, Speck Group
University of California, Santa Barbara
Trap-Assisted Auger-Meitner Recombination
in GaN p-i-n Diodes
GaN-based devices have already found massive success in applications from lighting to power conversion, where commercial phosphor-converted GaN-based light-emitting diodes already exhibit luminous efficacies above 200 lm/W, and commercial 1200V class lateral GaN-based power transistors are emerging in the market. For high-voltage vertical power devices, semiconductor materials with high predicted breakdown voltages that can be grown with thick and controllably lightly doped i-regions are critical, making GaN p-i-n diodes an ideal candidate, where devices from 1–5 kV have already been reported in the literature.
In this seminar, I will describe the electron emission-spectroscopy (EES) and -microscopy (EEM) studies of GaN p-i-n diodes. In EES and EEM, the surfaces of devices are activated to negative electron affinity with the deposition of cesium, allowing electrons to escape into vacuum where they can be measured. For standard operating conditions of the diodes, only overflow electrons at the conduction band minimum will emit from the surface. In EES, when measuring the current of emitted electrons of diodes with varying p-GaN thicknesses we measure the minority diffusion length of electrons to be Le = 26 ± 3 nm. In EEM, we spatially resolve the electron emission to measure the lateral current spread across a circular aperture which we find fits well with the analytical solutions of Joyce and Wemple [J. Appl. Phys. 41, 3818 (1970)]. Furthermore, in EES, when operating the diodes at current densities above ~70 A/cm^2, we measure hot electrons generated by trap-assisted Auger-Meitner recombination (TAAR). The measured high energy electron peaks correspond to electrons originating from conduction band satellite valleys located at 0.93 ± 0.16 eV, 1.68 ± 0.23 eV, and 2.64 ± 0.24 eV above the Γ valley of wurtzite GaN. This unexpected observation of TAAR in GaN p-i-n diodes at high carrier densities spotlights the importance of further studies of defects in GaN and the necessity to incorporate SRH, radiative, and TAAR capture steps of defect-assisted recombination cycles into device modeling, which will briefly be discussed.