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Proceedings Paper

Electrically conductive ZnO/GaN distributed Bragg reflectors grown by hybrid plasma-assisted molecular beam epitaxy
Author(s): Filip Hjort; Ehsan Hashemi; David Adolph; Tommy Ive; Åsa Haglund
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Paper Abstract

III-nitride-based vertical-cavity surface-emitting lasers have so far used intracavity contacting schemes since electrically conductive distributed Bragg reflectors (DBRs) have been difficult to achieve. A promising material combination for conductive DBRs is ZnO/GaN due to the small conduction band offset and ease of n-type doping. In addition, this combination offers a small lattice mismatch and high refractive index contrast, which could yield a mirror with a broad stopband and a high peak reflectivity using less than 20 DBR-pairs. A crack-free ZnO/GaN DBR was grown by hybrid plasma-assisted molecular beam epitaxy. The ZnO layers were approximately 20 nm thick and had an electron concentration of 1×1019 cm-3, while the GaN layers were 80-110 nm thick with an electron concentration of 1.8×1018 cm-3. In order to measure the resistance, mesa structures were formed by dry etching through the top 3 DBR-pairs and depositing non-annealed Al contacts on the GaN-layers at the top and next to the mesas. The measured specific series resistance was dominated by the lateral and contact contributions and gave an upper limit of ~10-3Ωcm2 for the vertical resistance. Simulations show that the ZnO electron concentration and the cancellation of piezoelectric and spontaneous polarization in strained ZnO have a large impact on the vertical resistance and that it could be orders of magnitudes lower than what was measured. This is the first report on electrically conductive ZnO/GaN DBRs and the upper limit of the resistance reported here is close to the lowest values reported for III-nitride-based DBRs.

Paper Details

Date Published: 16 February 2017
PDF: 9 pages
Proc. SPIE 10104, Gallium Nitride Materials and Devices XII, 1010413 (16 February 2017); doi: 10.1117/12.2250126
Show Author Affiliations
Filip Hjort, Chalmers Univ. of Technology (Sweden)
Ehsan Hashemi, Chalmers Univ. of Technology (Sweden)
David Adolph, Chalmers Univ. of Technology (Sweden)
Tommy Ive, Chalmers Univ. of Technology (Sweden)
Åsa Haglund, Chalmers Univ. of Technology (Sweden)


Published in SPIE Proceedings Vol. 10104:
Gallium Nitride Materials and Devices XII
Jen-Inn Chyi; Hiroshi Fujioka; Hadis Morkoç; Yasushi Nanishi; Ulrich T. Schwarz; Jong-In Shim, Editor(s)

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