Electrically conductive ZnO/GaN distributed Bragg reflectors grown by hybrid plasma-assisted molecular beam epitaxy

Filip Hjort; Ehsan Hashemi; David Adolph; Tommy Ive; Åsa Haglund

doi:10.1117/12.2250126

16 February 2017 Electrically conductive ZnO/GaN distributed Bragg reflectors grown by hybrid plasma-assisted molecular beam epitaxy

Filip Hjort, Ehsan Hashemi, David Adolph, Tommy Ive, Åsa Haglund

Author Affiliations +

Proceedings Volume 10104, Gallium Nitride Materials and Devices XII; 1010413 (2017) https://doi.org/10.1117/12.2250126
Event: SPIE OPTO, 2017, San Francisco, California, United States

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.

Conference Presentation

Citation Download Citation

Filip Hjort, Ehsan Hashemi, David Adolph, Tommy Ive, and Åsa Haglund "Electrically conductive ZnO/GaN distributed Bragg reflectors grown by hybrid plasma-assisted molecular beam epitaxy", Proc. SPIE 10104, Gallium Nitride Materials and Devices XII, 1010413 (16 February 2017); https://doi.org/10.1117/12.2250126

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