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Title: Solid immersion lenses for enhancing the optical resolution of thermal and electroluminescence mapping of GaN-on-SiC transistors

Abstract

Solid immersion lenses (SILs) are shown to greatly enhance optical spatial resolution when measuring AlGaN/GaN High Electron Mobility Transistors (HEMTs), taking advantage of the high refractive index of the SiC substrates commonly used for these devices. Solid immersion lenses can be applied to techniques such as electroluminescence emission microscopy and Raman thermography, aiding the development device physics models. Focused ion beam milling is used to fabricate solid immersion lenses in SiC substrates with a numerical aperture of 1.3. A lateral spatial resolution of 300 nm is demonstrated at an emission wavelength of 700 nm, and an axial spatial resolution of 1.7 ± 0.3 μm at a laser wavelength of 532 nm is demonstrated; this is an improvement of 2.5× and 5×, respectively, when compared with a conventional 0.5 numerical aperture objective lens without a SIL. These results highlight the benefit of applying the solid immersion lenses technique to the optical characterization of GaN HEMTs. Further improvements may be gained through aberration compensation and increasing the SIL numerical aperture.

Authors:
;  [1]
  1. Center for Device Thermography and Reliability (CDTR), H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom)
Publication Date:
OSTI Identifier:
22492805
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 118; Journal Issue: 14; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; APERTURES; ELECTROLUMINESCENCE; ELECTRON MOBILITY; GALLIUM NITRIDES; ION BEAMS; LENSES; MICROSCOPY; REFRACTIVE INDEX; SILICON CARBIDES; SPATIAL RESOLUTION; SUBSTRATES; THERMOGRAPHY; TRANSISTORS; WAVELENGTHS

Citation Formats

Pomeroy, J. W., E-mail: James.Pomeroy@Bristol.ac.uk, and Kuball, M. Solid immersion lenses for enhancing the optical resolution of thermal and electroluminescence mapping of GaN-on-SiC transistors. United States: N. p., 2015. Web. doi:10.1063/1.4932029.
Pomeroy, J. W., E-mail: James.Pomeroy@Bristol.ac.uk, & Kuball, M. Solid immersion lenses for enhancing the optical resolution of thermal and electroluminescence mapping of GaN-on-SiC transistors. United States. doi:10.1063/1.4932029.
Pomeroy, J. W., E-mail: James.Pomeroy@Bristol.ac.uk, and Kuball, M. Wed . "Solid immersion lenses for enhancing the optical resolution of thermal and electroluminescence mapping of GaN-on-SiC transistors". United States. doi:10.1063/1.4932029.
@article{osti_22492805,
title = {Solid immersion lenses for enhancing the optical resolution of thermal and electroluminescence mapping of GaN-on-SiC transistors},
author = {Pomeroy, J. W., E-mail: James.Pomeroy@Bristol.ac.uk and Kuball, M.},
abstractNote = {Solid immersion lenses (SILs) are shown to greatly enhance optical spatial resolution when measuring AlGaN/GaN High Electron Mobility Transistors (HEMTs), taking advantage of the high refractive index of the SiC substrates commonly used for these devices. Solid immersion lenses can be applied to techniques such as electroluminescence emission microscopy and Raman thermography, aiding the development device physics models. Focused ion beam milling is used to fabricate solid immersion lenses in SiC substrates with a numerical aperture of 1.3. A lateral spatial resolution of 300 nm is demonstrated at an emission wavelength of 700 nm, and an axial spatial resolution of 1.7 ± 0.3 μm at a laser wavelength of 532 nm is demonstrated; this is an improvement of 2.5× and 5×, respectively, when compared with a conventional 0.5 numerical aperture objective lens without a SIL. These results highlight the benefit of applying the solid immersion lenses technique to the optical characterization of GaN HEMTs. Further improvements may be gained through aberration compensation and increasing the SIL numerical aperture.},
doi = {10.1063/1.4932029},
journal = {Journal of Applied Physics},
number = 14,
volume = 118,
place = {United States},
year = {Wed Oct 14 00:00:00 EDT 2015},
month = {Wed Oct 14 00:00:00 EDT 2015}
}
  • Hot electrons in AlGaN/GaN high electron mobility transistors are studied during radio frequency (RF) and DC operation by means of electroluminescence (EL) microscopy and spectroscopy. The measured EL intensity is decreased under RF operation compared to DC at the same average current, indicating a lower hot electron density. This is explained by averaging the DC EL intensity over the measured load line used in RF measurements, giving reasonable agreement. In addition, the hot electron temperature is lower by up to 15% under RF compared to DC, again at least partially explainable by the weighted averaging along the specific load line.more » However, peak electron temperature under RF occurs at high V{sub DS} and low I{sub DS} where EL is insignificant suggesting that any wear-out differences between RF and DC stress of the devices will depend on the balance between hot-carrier and field driven degradation mechanisms.« less
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  • We describe a technique for fabricating micro- and nanostructures incorporating fluorescent defects in diamond with a positional accuracy better than hundreds of nanometers. Using confocal fluorescence microscopy and focused ion beam etching, we initially locate a suitable defect with respect to registration marks on the diamond surface then etch a structure using these coordinates. We demonstrate the technique by etching an 8 {mu}m diameter hemisphere positioned with single negatively charged nitrogen-vacancy defect lies at its origin. Direct comparison of the fluorescence photon count rate before and after fabrication shows an eightfold increase due to the presence of the hemisphere.
  • Recent efforts to define microscopic solid-immersion-lenses (SIL) by focused ion beam milling into diamond substrates that are registered to a preselected single photon emitter are summarized. We show how we determine the position of a single emitter with at least 100 nm lateral and 500 nm axial accuracy, and how the milling procedure is optimized. The characteristics of a single emitter, a Nitrogen Vacancy (NV) center in diamond, are measured before and after producing the SIL and compared with each other. A count rate of 1.0 × 10{sup 6} counts/s is achieved with a [111] oriented NV center.