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Appl Opt ; 55(26): 7387-91, 2016 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-27661378


The influence of the microstructure geometry of patterned sapphire substrates (PSS) on the light extraction efficiency (LEE) of GaN light-emitting diodes (LEDs) is numerically analyzed. Cone structures of various dimensions are studied, along with dome and mixed microstructures. LEE is found to mainly depend on the microstructure surface slope. LEE rises quickly with slope and flattens out when the slope exceeds 0.6. Scaling down the microstructure has little effect on LEE. Light rays are found to travel longer distances in PSS LEDs, as compared with LEDs grown on a flat substrate. Keeping GaN absorption loss low is important for LEE optimization.

Opt Express ; 23(24): 31150-62, 2015 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-26698744


The combination of ZnO, InN, and GaN epitaxial layers is explored to provide long wavelength photodetection capability in the GaN based materials. Growth temperature optimization was performed to obtain the best quality of InN epitaxial layer in the MOCVD system. The temperature dependent photoluminescence (PL) can provide the information about thermal quenching in the InN PL transitions and at least two non-radiative processes can be observed. X-ray diffraction and energy dispersive spectroscopy are applied to confirm the inclusion of indium and the formation of InN layer. The band alignment of such system shows a typical double heterojunction, which is preferred in optoelectronic device operation. The photodetector manufactured by this ZnO/GaN/InN layer can exhibit extended long-wavelength quantum efficiency, as high as 3.55%, and very strong photocurrent response under solar simulator illumination.

Opt Express ; 23(24): A1434-41, 2015 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-26698792


This work demonstrates the enhanced power conversion efficiency (PCE) in InGaN/GaN multiple quantum well (MQWs) solar cells with gradually decreasing indium composition in quantum wells (GQWs) toward p-GaN as absorber. The GQW can improve the fill factor from 42% to 62% and enhance the short current density from 0.8 mA/cm2 to 0.92 mA/cm2, as compares to the typical MQW solar cells. As a result, the PCE is boosted from 0.63% to 1.11% under AM1.5G illumination. Based on simulation and experimental results, the enhanced PCE can be attributed to the improved carrier collection in GQW caused by the reduction of potential barriers and piezoelectric polarization induced fields near the p-GaN layer. The presented concept paves a way toward highly efficient InGaN-based solar cells and other GaN-related MQW devices.