Semiconductor devices and their fabrication

Abstract

A method of selectively etching one semiconductor material layer (4) of a multilayer structure which underlies another layer, a top layer (1), of the same or a similar semiconductor material without significantly affecting the top layer (1). The method involves pre-etching both layers (1,4) to provide a stepped structure with recesses (10) under an intermediate layer (5), providing r.f. deposited silicon dioxide (11) over the etched structure such that it is thinnest in the recesses (10) from which it is subsequently selectively removed and etching the layer (4) to the required extent while the top layer (1) is still covered by r.f. silicon dioxide. The method may be used in the manufacture of mass transport buried heterostructure lasers with the layers 1 and 4 of GaInAsP and layers 3 and 5 of InP, the recesses (10) subsequently being filled with InP by a mass transport process. Top layer (1) and intermediate layer (5) may be p-type and layer 3 n-type, top layer ( 1) providing an electrical contacting layer for the laser.