Photo-assisted wet (PAW) etching for laser fabrication

Modern day technology uses discrete optical components including laser diodes and integrated electronic circuits. Fabricating an etched mirror laser is one of the major tasks to realize integrated optics. While dry etching is the most widely accepted process to fabricate optoelectronic devices, wet etching has potential advantages including lower cost, smoother surfaces, and faster etching rate. However typical wet etching does not provide a viable alternative for the demanding process of fabricating vertical side walls with low lateral etch rates. The application of the wet etching to the production of vertical sidewalls has been a significant problem for several decades.;The primary accomplishments of the research consists of developing processes, apparatus, and models for the Photo-Assisted Wet (PAW) etching that uses light directed perpendicular to the surface of a wafer in order to alter the typical crystal-plane etching and thereby control the sidewall profile. The new techniques demonstrate integrated laser mirrors in III-V laser heterostructure. These mirrors achieve as high as 93% of the reflectance of the cleaved mirror with negligible dependence on the crystal orientation.;The research explores the PAW etching process using both coherent (lasers) and incoherent (LEDs) illumination for different types of materials including bulk GaAs and III-V laser heterostructure. The effects of different wavelengths, intensities and wafer masking structures are investigated. Specific combinations control the sidewall profile and etching characteristics to produce on-demand etch-stop layers and sidewall angles ranging from 0 to 90°. Laser heterostructure etched with coherent illumination shows unexpected results for heterostructure including non-uniform etch depth linked to the masking materials and surface density of excess carriers.;New apparatus was designed and applied to the PAW etching for the fabrication of III-V devices. The apparatus has in-situ, real-time systems including (i) an optical system to expand, filter and dither the etching beam, (ii) a pulsed-laser wet etch monitor to determine the etch depth, rate, formation of surface microstructure and transition layers in a preselected region of the sample, (iii) a steady-state photoluminescence (PL) monitor with CCD array and Photo Detector (PD) to provide (2-D) spatially-resolved and integrated measurements of PL during the etching.