Laser-Assisted Selective Chemical Etching for Active Trimming of GaAs Waveguide Devices

Abstract

In the fabrication of III-V integrated optic and microelectronic devices, there is a need for improved etching processes. As reported previously [1], laser-assisted wet chemical etching techniques have been developed for alloy-selective patterning of GaAs/AlGaAs layered structures. Such techniques are potentially very important for the fabrication of a large variety of hetero-structure devices. These techniques have utilized a CW dye laser tuned to a wavelength above the band edge of GaAs, but below that of the AlGaAs layer (e.g., a wavelength of 0.85 μm) to etch GaAs. Using the laser spot to spatially define the etched area, selectivities in excess of 100 for GaAs over Al.40Ga.60As were achieved at etch rates in excess of 2 μm/min. Typical etch features are shown in Fig. 1. The feature on the left corresponded to an etch time of 15 sec, while the feature on the right, illustrating high selectivity at the AlGaAs interface, corresponded to an etch time of 45 sec. Recent studies, with an arrangement similar to that in Fig. 1, have shown that etch selectivity can be achieved based on differences in doping level and doping type as well as on differences in chemical composition.