Abstract
We demonstrate crack-free ZnO/GaN distributed Bragg reflectors (DBRs) grown by hybrid plasma-assisted molecular beam epitaxy using the same growth chamber for continuous growth of both ZnO and GaN without exposure to air. This is the first time these ZnO/GaN DBRs have been demonstrated. The Bragg reflectors consisted up to 20 periods as shown with cross-sectional transmission electron microscopy. The maximum achieved reflectance was 77% with a 32 nm wide stopband centered at 500 nm. Growth along both (0001) and (0001) directions was investigated. Low-temperature growth as well as two-step low/high-temperature deposition was carried out where the latter method improved the DBR reflectance. Samples grown along the (0001) direction yielded a better surface morphology as revealed by scanning electron microscopy and atomic force microscopy. Reciprocal space maps showed that ZnO(0001)/GaN reflectors are relaxed whereas the ZnO(0001)/GaN DBRs are strained. The ability to n-type dope ZnO and GaN makes the ZnO(0...
Highlights
We demonstrate crack-free ZnO/GaN distributed Bragg reflectors (DBRs) grown by hybrid plasma-assisted molecular beam epitaxy using the same growth chamber for continuous growth of both ZnO and GaN without exposure to air
Lowtemperature growth as well as two-step low/high-temperature deposition was carried out where the latter method improved the DBR reflectance
Reciprocal space maps showed that ZnO(0001 ̄)/GaN reflectors are relaxed whereas the ZnO(0001)/GaN DBRs are strained
Summary
We demonstrate crack-free ZnO/GaN distributed Bragg reflectors (DBRs) grown by hybrid plasma-assisted molecular beam epitaxy using the same growth chamber for continuous growth of both ZnO and GaN without exposure to air. The second approach involves epitaxial growth of the active region followed by lift-off to separate the active region from the substrate and flip-chip bonding where the active region is sequentially bonded to the top and bottom dielectric DBRs.[1,4,5,6,10,11,12,13] This method achieves high-reflectance mirrors with wide stopbands using only a few periods while avoiding all the challenges related aElectronic address: adolph@chalmers.se 2166-532X/2016/4(8)/086106/8
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