Semiconductor etching methods

A method of etching into one or more epitaxial layers of III-V, III-N or II-VI semiconductor material(s) in a semiconductor structure 30 is disclosed. The semiconductor structure is a vertical cavity surface emitting laser (VCSEL, Figure 2), light-emitting diode (LED, Figure 4) or photodiode (Figure 5). The method comprises process steps of establishing a flow of an etch gas mixture through a plasma processing chamber (2, Figure 1) and generating a plasma within the chamber. A radio frequency (RF) bias voltage is simultaneously applied to a support table (14, Figure 1) within the chamber on which the semiconductor structure, carrying a patterned mask 39, is placed. More than 90% of the etch gas mixture consists of a mixture of silicon tetrachloride (SiCl4) and nitrogen (N2). The etch gas mixture may comprise one or more inert gases such as helium, and preferably does not contain more than a trace level of boron trichloride (BCl3). The semiconductor material(s) may be any of GaN, GaAs, AlGaAs, InGaAs or AlInGaP.