Distributed feedback (DFB) single frequency InGaN/GaN laser diodes at visible wavelengths can find many important emerging applications in optical communication, sensing, etc. Unlike GaAs- and InP-based DFB lasers, a reliable dry-etching process technology for creating nanometer-size gratings in this material is not well-developed. As a result, most InGaN/GaN DFB lasers demonstrated today give relatively low yield and low wall-plug efficiency. In this paper, Zhang et al. introduced a viable technique to address this problem. Instead of defining the grating on InGaN/GaN layers, a phase-shifted grating is created on a thin hydrogen silsesquioxane (HSQ), a photoresist commonly used for fine resolution electron-beam lithography, that was spun coated on the surface of the p-InGaN layer. High performance DFB lasers with record optical power (400 mW) and wall-plug efficiency are demonstrated. This practical method significantly eases the fabrication process for a visible-wavelength DFB laser and opens new opportunities for the fabrication of future complex photonic integrated circuits (PICs) on InGaN/GaN materials.
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