Optimized ZnSe:N/ZnTe:N contact structure of ZnSe-based II–VI laser diodes

We have established the basic stability of ZnSe:N/ZnTe:N superlattice (SL) contact needed for 1000 h of operation. We have fabricated ZnCdSe/ZnSSe/ZnMgSSe separated confinement heterostructure laser diodes with the ZnTe:N contact layer/ZnSe:N/ZnTe:N SL/ZnSe:N cap layer to achieve a low voltage (<5 V) at $\text{500\hspace{0.17em}}{\mathrm{A\hspace{0.17em}cm}}^{\mathrm{-2}}$ constant current for 1000 h (electrode test) by the reduction of the thickness of the ZnTe:N contact layer and by the optimization of the N concentration in the ZnSe:N cap layer. We found that, when the thickness of the ZnTe:N contact layer becomes 4 nm, the reduction of $N_A{\mathrm{–N}}_D$ in the ZnSe:N cap layer is prevented, and the defect density in the vicinity of the ZnSe:N/ZnTe:N SL is reduced. It is assumed that the reduction of $N_A{\mathrm{–N}}_D$ in ZnSe:N is caused by the stress in the ZnSe:N cap layer induced by a large lattice mismatch between ZnTe and ZnSe. We confirmed that the reduction of stress in the ZnSe:N layer and the reduction of the structural defect density were achieved by the reduction of the thickness of ZnTe to 4 nm.