Deep levels and shallow-deep transitions in ZnSe/Zn1− Mn Se superlattices

A theory of deep impurity levels in superlattices is outlined, and applied to ZnSe/Zn0.5Mn0.5Se with the substitutional dopant GaZn. Ga is predicted to undergo a shallow-deep transition as a function of x in bulk Zn1 − xMnxSe, and so Ga dopes ZnSe n-ty but prevents Zn0.5Mn0.5Se from being doped n-type even by modulation doping. In ZnSe/Zn0.5Mn0.5Se superlattices, the band edges are quite sensitive to changes in the layer thicknesses, but the deep levels are not. As a result, shallow-deep transitions as functions of layer thickness are predicted to occur. The physics of shallow-deep transitions in superlattices is elucidated, and its relevance to the II–VI doping problem is discussed.