Characterization of buried heterostructure lasers by scanning capacitance microscopy

Zn-Fe interdiffusion is an important issue in InP-based buried heterostructure lasers that utilise Zn for p doping and Fe for the semi-insulating layers. In this work, cross-sectional scanning capacitance microscopy (SCM) is used to characterise these laser structures. The capability of the SCM technique to analyse such complex devices is demonstrated. The SCM images (on as-cleaved samples) show that diffusion of Zn into the semi-insulating layer is significant and extends as far as 0.7 μm. Similar values (about 0.5 μm) were obtained by atomic force microscopy (AFM) investigations on samples etched with a dopant selective etchant. Further, the SCM images are shown to give additional useful information on the active doping levels in the different layers and the location of the (electrical) p-n junctions. Finally, the mechanisms for the contrast in the SCM images are discussed