Abstract: A semiconductor laser device structure comprising an active region provided by a quantum well of an indirect bandgap material, the quantum well being divided laterally to form an active region comprising a two dimensional array of localized cells. Preferably the quantum well of indirect band gap material is selected from group IV semiconductor materials and comprises a silicon-germanium alloy. A silicon/silicon-germanium alloy multi-quantum well (MQW) structure is described. In a preferred embodiment, a Si/SiGe alloy MQW laser diode comprises a coplanar double grating configuration etched through the MQW structure to provide distributed feedback. The double intersecting grating structure functions to define an array of "cells" or regions of finite dimensions in the quantum well structure which "localize" carriers within the cells thereby enhancing the radiative emission probability. The grating also provides for combined gain-coupled and index-coupled distributed feedback.