The doping problem in II-VI-compounds and its consequences for wide gap II-VI devices

We describe total energy calculations based on density functional theory of defect complexes in ZnSe containing nitrogen. As a main result, a complex of a nitrogen interstitial with a selenium vacancy, which results from a movement of a nitrogen atom from the substitutional to the interstitial site, is much more stable than the nitrogen acceptor. We show that the typical signatures of such a complex can be detected in optical degradation experiments on stacking-fault-free ZnSe based laser diodes. The degradation process can thus be understood as a decay of the thermodynamically unstable nitrogen acceptor. From theoretical considerations, this process is predicted to be influencable by strain engineering and the admixture of tellurium to the p-layer. On a prototype device we demonstrate that a combination of these measures in fact leads to a drastic lifetime increase of devices.