Mirror formation by chemical etching and microcleaving of InP-based lasers

Abstract

This paper outlines two chemical-etch techniques by which processed laser mirrors can be obtained. These are (i) direct etching and (ii) the etching of bridges or cantilevers that can be "microcleaved" to produce small local mirror surfaces. Both techniques rely on the crystallographic selectivity of chemical etchants.Direct etching of mirrors is accomplished using HCl–HNO3–H3PO4–H2SO4 mixtures. This approach produces smooth surfaces with vertical walls in InP and a slight bevel in the GaInAsP active layers. Lasers made with direct etched mirrors showed threshold currents comparable to normal cleaved mirror lasers.For microcleaving, cantilevers were etched in 1–2% Br2–CH3OH solutions initially in InP wafers. Cantilevers, however, could not be obtained directly on double heterostructure InP–InGaAsP lasers with a ternary (GaInAs) capping layer. Owing to severe sideways etching of the ternary under the SiO2 mask, the negative slopes necessary for cantilever formation never developed. To form laser structures, we had to completely remove the ternary top layer from all areas exposed to the Br2– CH3OH etch solution. Properly formed cantilevers were then obtained.