Dependence of Electron Overflow on Emission Wavelength and Crystallographic Orientation in Single-Quantum-Well III–Nitride Light-Emitting Diodes

Kawaguchi, Yoshinobu; Huang, Shih Chieh; Zhao, Yuji; Speck, James S.; DenBaars, Steven P.; Nakamura, Shuji

doi:10.7567/apex.6.052103

Cited by 3 publications

(1 citation statement)

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“…A vertically uniform carrier distribution among the QWs is a challenge in all GaN-based light-emitters 83,84 due to the large difference between the activation energy of donor and acceptor impurities 85 , the strong imbalance between electron and hole mobilities 86 , the large band offsets and, possibly even more critical, the spontaneous and piezoelectric polarization effects at heterointerfaces 87,88 . In order to maximize the radiative recombination in the QWs, one should minimize current crowding 89,90 as well as carrier leakage beyond the active region, which can involve both electrons [91][92][93] and holes 94 and could be enhanced by Auger 95,96 and excited subband recombination 97 . Electrons can be prevented from leaking into the p-GaN layers by inserting an energy barrier in the conduction band between QWs and p-layers, a socalled electron-blocking layer (EBL).…”

Section: Carrier Transport and Optical Gainmentioning

confidence: 99%

Progress and challenges in electrically pumped GaN-based VCSELs

et al. 2016

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The Vertical-Cavity Surface-Emitting Laser (VCSEL) is an established optical source in short-distance optical communication links, computer mice and tailored infrared power heating systems. Its low power consumption, easy integration into two-dimensional arrays, and low-cost manufacturing also make this type of semiconductor laser suitable for application in areas such as high-resolution printing, medical applications, and general lighting. However, these applications require emission wavelengths in the blue-UV instead of the established infrared regime, which can be achieved by using GaN-based instead of GaAs-based materials. The development of GaN-based VCSELs is challenging, but during recent years several groups have managed to demonstrate electrically pumped GaN-based VCSELs with close to 1 mW of optical output power and threshold current densities between 3-16 kA/cm 2 . The performance is limited by challenges such as achieving high-reflectivity mirrors, vertical and lateral carrier confinement, efficient lateral current spreading, accurate cavity length control and lateral optical mode confinement. This paper summarizes different strategies to solve these issues in electrically pumped GaN-VCSELs together with state-of-the-art results. We will highlight our work on combined transverse current and optical mode confinement, where we show that many structures used for current confinement result in unintentionally optically anti-guided resonators. Such resonators can have a very high optical loss, which easily doubles the threshold gain for lasing. We will also present an alternative to the use of distributed Bragg reflectors as high-reflectivity mirrors, namely TiO2/air high contrast gratings (HCGs). Fabricated HCGs of this type show a high reflectivity (>95%) over a 25 nm wavelength span.

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