Date/Time: 04-23-2019 - Tuesday - 05:00 PM - 07:00 PM
Zoey Warecki1 Andrew Armstrong2 Alec Talin2 John Cumings1

1, University of Maryland, College Park, Maryland, United States
2, Sandia National Laboratories, Livermore, California, United States

Gallium nitride offers several advantages over current silicon based devices, such as high-temperature applications, high-power electronics, and space-based or other high radiation exposure applications [1]. Measurements of the minority carrier diffusion length in GaN can be studied using cathodoluminescence (CL) or electron beam induced current (EBIC) in a scanning electron microscope (SEM). However, as recently reported in Yakimov et. al., the EBIC planar geometry in SEM often leads to an over estimation of the minority carrier diffusion length in n-type GaN [2]. This over estimation is attributed to the interaction volume in SEM, which is on the order of hundreds of nanometers to a few microns and within the same order of magnitude as reported minority carrier diffusion lengths of n-GaN, which are reported to be between a few tens of nanometers to a few microns. Instead of SEM EBIC, we use bulk scanning transmission electron microscopy (STEM) EBIC to measure the minority carrier diffusion length in n-GaN. Our sample consists of a high purity single crystal n-type GaN substrate (275 µm thick) grown by hydride vapor phase epitaxy (HVPE) with a threading dislocation density of ~106/cm2 and patterned with a nickel Schottky contact as well as an indium ohmic contact. Using a 100 kV or 200 kV accelerating voltage causes the interaction volume in our bulk specimen to be large enough to separate from the minority carrier diffusion length. We then fit the STEM EBIC line profiles in order to determine the minority carrier diffusion length of n-GaN as well as the interaction volume. In addition, we have imaged the growth of the depletion edge during an applied reverse bias, and indirectly measure the depletion width at zero applied bias.

This research was performed at the University of Maryland NanoCenter Advanced Imaging and Microscopy Laboratory. The data was taken on a JEOL 2100F TEM operating at 100kV and 200 kV in STEM mode using a Nanofactory STM-TEM holder.

[1] S.J. Pearton, et al., ECS J. Solid State Sci. Technol., 5, Q35, (2016)
[2] E.B Yakimov, J. Alloys Compd., 627, p 344-351, (2015)

The authors acknowledge funding from Nanostructures for Electrical Energy Storage (NEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE 1322106, and support from NIST Grant No. 70NANB15H218. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC0494AL85000.

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