Investigation of Sidewall Recombination in GaN Using a Quantum Well Probe
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Investigation of Sidewall Recombination in GaN Using a Quantum Well Probe E. D. Haberer, M. Woods, A. Stonas1, C-H. Chen1, S. Keller1, M. Hansen, U. Mishra1, S. DenBaars, J. Bowers1, E. L. Hu1 Materials Department, University of California, Santa Barbara, California, 93106 1 Dept. of Elect. and Comp. Eng., University of California, Santa Barbara, California, 93106 ABSTRACT In this study, we use a quantum well (QW) probe structure to explore the size dependent effects of sidewall recombination in GaN. Mesas 0.8-7 µm in width with pitches of 4 µm, 8 µm, and 12 µm were etched into the QW probe structure, exposing the QW at the sidewalls. Several etch conditions were investigated. Room temperature photoluminescence (PL) measurements, using a He-Cd laser as an excitation source and laser spot size of approximately 230 µm, were taken before and after the mesas were etched. The effects of sidewall formation were quantified by comparing the maximum PL intensity of the QW before and after etch. Higher remaining PL intensity was observed for etch conditions which used both Ar ions and Cl2 gas instead of only Ar ions. The fraction of remaining PL decreased with decreasing mesa width, however the remaining PL intensity was relatively large even for small features. The preliminary data suggested that GaN is relatively insensitive to sidewall damage.
INTRODUCTION As GaN material and device technology matures, there is growing interest in scaling devices to smaller dimensions. In doing so, it is important to consider the effects of air/semiconductor interfaces on device performance. Depending on the nature of the surface states and bond reconstruction, the air/semiconductor interface can be a source of nonradiative recombination. As the surface area to volume ratio increases, as in smaller optical devices, nonradiative sidewall recombination can become an increasingly dominant mechanism of recombination. In GaAs- and InP-based materials sidewall recombination limits the scaling of lasers (in-plane and VCSELs) to a few microns and thus necessitates either regrowth or surface passivation [1]. Scaling effects have yet to be fully characterized in GaN. Dry etch processes are critical to the development of high resolution GaN device technologies. Dry etch processes combine a chemical component, such as Cl2 gas, and physical component, such as low energy Ar+ ions, to remove material and create anisotropic profiles. The physical bombardment, which is a necessary part of the dry etching process, can create extensive lattice damage that may be deleterious to the optical and electrical properties of the material. As material is removed during etch, bonds are broken and new surfaces are created. The physical nature of dry etching exacerbates the problem. Incoming ions can ricochet off the material surface causing subsurface lateral damage. In this study, we use an InGaN/GaN quantum well (QW) probe structure to investigate the effects of sidewall damage on the optical properties of GaN.
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EXPERIMENTAL DETAILS The QW probe structure
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