Design and fabrication of air/semiconductor Bragg gratings for short wavelength nitride-based lasers

Summary form only given. Blue/ultraviolet emitting diode lasers, based on nitride compounds, are suitable for spectroscopy, gas analysis, optical data storage, laser printing and scanning. Many of these applications require low-threshold devices with high output powers, high quality beam profile, and stable single-frequency emission. We have recently demonstrated a simple post-processing technique which improves some of these device characteristics. A significant reduction in both the threshold current and spectral linewidth of InGaN MQW lasers has been achieved by introducing a 5/spl lambda//4 air/nitride Bragg grating defined by focused ion beam (FIB) etching. In this paper, some of the design and fabrication parameters which determine the characteristics of the air/nitride reflectors are theoretically and experimentally investigated. It is found that the etch depth of the grating structure plays an important role in controlling both the degree of threshold reduction and the mode selectivity introduced by the mirror structure. Decreasing the etch depth, by lowering the FIB ion dose from 5000 to 4000 pC//spl mu/m/sup 2/, reduces the threshold reduction from 13% to 7%; however, it introduces a 63% reduction in spectral linewidth. These observations are modeled in terms of spatial and spectral mode selectivity.