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Crystals 2017, 7(7), 187; doi:10.3390/cryst7070187

Transparency of Semi-Insulating, n-Type, and p-Type Ammonothermal GaN Substrates in the Near-Infrared, Mid-Infrared, and THz Spectral Range

1
AMMONO S. A, Prusa 2, 00-493 Warsaw, Poland
2
Department of Experimental Physics, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
3
Institute of High Pressure Physics, Polish Academy of Science, Sokołowska 29/37, 01-142 Warsaw, Poland
*
Author to whom correspondence should be addressed.
Received: 10 May 2017 / Revised: 16 June 2017 / Accepted: 21 June 2017 / Published: 25 June 2017
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Abstract

GaN substrates grown by the ammonothermal method are analyzed by Fast Fourier Transformation Spectroscopy in order to study the impact of doping (both n- and p-type) on their transparency in the near-infrared, mid-infrared, and terahertz spectral range. It is shown that the introduction of dopants causes a decrease in transparency of GaN substrates in a broad spectral range which is attributed to absorption on free carriers (n-type samples) or dopant ionization (p-type samples). In the mid-infrared the transparency cut-off, which for a semi-insulating GaN is at ~7 µm due to an absorption on a second harmonic of optical phonons, shifts towards shorter wavelengths due to an absorption on free carriers up to ~1 µm at n ~ 1020 cm−3 doping level. Moreover, a semi-insulating GaN crystal shows good transparency in the 1–10 THz range, while for n-and p-type crystal, the transparency in this spectral region is significantly quenched below 1%. In addition, it is shown that in the visible spectral region n-type GaN substrates with a carrier concentration below 1018 cm−3 are highly transparent with the absorption coefficient below 3 cm−1 at 450 nm, a satisfactory condition for light emitting diodes and laser diodes operating in this spectral range. View Full-Text
Keywords: GaN; infrared spectral range; THz spectral range; free-carrier absorption GaN; infrared spectral range; THz spectral range; free-carrier absorption
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Kucharski, R.; Janicki, Ł.; Zajac, M.; Welna, M.; Motyka, M.; Skierbiszewski, C.; Kudrawiec, R. Transparency of Semi-Insulating, n-Type, and p-Type Ammonothermal GaN Substrates in the Near-Infrared, Mid-Infrared, and THz Spectral Range. Crystals 2017, 7, 187.

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