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Recent progress in dry etching technology of GaInAsP/InP compounds enabled realizations of fine vertical groove structures with a high aspect ratio. Since this technology enables the formation of etched mirrors in a wafer batch process, it leads to a low-cost production of not only simple Fabry-Perot lasers but also high performance and functional lasers for optical communications by integrating functional elements such as gratings for wavelength selection and high-reflectivity/low-reflectivity facets, while improvements in the size controllability with precision are still required.
In order to keep an initial mask width condition during reactive-ion-etching (RIE) with methane/hydrogen mixture gas, we developed a sequential etching process of the RIE followed by oxygen ashing for relatively short period (for the etching depth of around 240 nm) and repeated the process for required etching depth. The tilt angle of the etched facet was controlled to be less than 1 degree from the normal to the wafer, and the aspect ratio of a narrow groove (140 nm) as high as 17 was obtained. By using this technique we could realize high-reflectivity distributed Bragg reflector (DBR) consisting of semiconductor/polymer pillars and DBR lasers with low threshold current (less than 10 mA for the stripe width of 5 micronmeter) and high differential quantum efficiency of 50 % from the front facet, while the emission spectrum showed a multi-mode operation due to poor wavelength selectivity. A preliminary aging test was carried out at room temperature CW condition, and no degradation was observed after 5,000 hours.
With aiming at high performance single-wavelength lasers, we realized a novel distributed feedback (DFB) laser consisting of the first-order corrugations on the sidewalls of the stripe mesa, named ?gVertical Grating (VG),?h as well as a distributed reflector (DR) laser consisting of the VG-DFB structure and above mentioned DBR on the rear side. A stable single-mode operation with a sub-mode suppression ratio of 36dB, thre
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