Semi-conductor lasers

In a semi-conductor laser comprising a plurality of epitaxial layers and a buried active laser layer characterised in that said active laser layer is located between a layer of n-type material and a layer of p-type material, the n-type layer and the p-type layer together having a trapezoidal cross-sectional shape, the sides of said active laser layer and at least a portion of each of said n-type layer and said p-type layer being covered by a plurality of thin layers which are substantially planar whereby the ends of a first, second and third portion of said plurality of thin layers abut the sides of said n-type layer, said active laser layer and said p-type layer, respectively, said plurality of thin layers having a doping sequence such that a plurality of p-n junctions is formed by said plurality of thin layers and said first portion of said plurality of thin layers forming at least one p-n junction below said active laser layer.