Electrical contacts on MOVPE-Grown ZnSe based laser diodes

The electrical characterization of metal contacts to Cl and N-doped ZnSe material systems is reported. Metalorganic vapor phase epitaxy (MOVPE) was used to grow the doped ZnSe samples at 330°C. With intentional chlorine doping using 1-chlorobutane, free electron concentrations of up to 8×10¹⁷ cm^-3 have been achieved. Photoluminescence (PL) spectra in conjunction with scanning transmission electron microscopy (SEM) were used to verify the layer properties. The turn-on voltage (V_T) of Ti/Pd/Au contact on the Cl-doped ZnSe epitaxial layer was significantly reduced by etching the ZnSe surface in NaOH, which was found to be due to removal of the native oxide layer grown on the ZnSe surface. Current-voltage (I-V), capacitance-voltage (C-V) measurements were used to investigate the junction properties of the Au/ZnSe:N structure before and after heat treatment at 400°C for 15 min. in N₂ atmosphere. The results indicated that the annealing procedure leads to redistribution of impurities and improves the electrical properties of the samples. C-V measurements on ZnSe:N show semi-insulating behaviour before annealing. However, after heat treatment the layer shows p-type conduction with an acceptor concentration of the order of 2×10¹⁶ cm^-3