| 摘要 |
In semiconductor layer structures in which at least two semiconductor layers having different thicknesses and consisting of different semiconductor materials are present, mesas can be formed by means of wet-chemical etchants and with the use of a mask. A disadvantage of the etchants available is that it is difficult to form mesas having substantially flat side walls with a small under-etching and with an accurately determined width, especially of the thinner layer. This is an unfavourable starting situation for the manufacture of, for example, radiation guides and semiconductor diode lasers, in which such mesas are formed. In the method according to the invention, the upper and thicker of the two semiconductor layers is etched by means of a selective and preferential etchant, substantially no underetching occurring with respect to the mask. Subsequently, the lower and thinner semiconductor layer and a part of the upper semiconductor layer are converted by a substantially non-selective anodic oxidation into semiconductor material oxides, which are removed by means of an etchant which is non-selective with respect to the oxides formed, but is selective with respect to the semiconductor materials. As a result, mesas are obtained having a substantially flat side wall, the lateral dimension of these mesas being accurately determined by the size of the mask. Thus, particularly favourable results are obtained, especially in the InP/InGaAsP material system. The method according to the invention can be used very advantageously when the thinner layer forms part of a so-called multilayer quantum well structure. In a particular embodiment, a further mask is provided above the mask in such a manner that it projects beyond the mask, the side walls of the mesa being made substantially straight, as a result of which the method is particularly suitable for providing by means of OMVPE further semiconductor layers on either side of the mesa, which results in a substantially flat buried structure. |
