Development of Ohmic contact materials for ZnSe-based blue light emitting devices

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In order to explore a possibility to prepare low resistance Ohmic contacts by the conventional deposition and annealing (DA) technique, the effects of the ZnSe surface cleaning and formation of an intermediate heterostructure on the electrical properties at the metal/semiconductor interface have been investigated for the N-doped p-ZnSe substrates grown by the molecular beam epitaxy (MBE) technique. The turn-on voltage (V_T) (corresponding to the breakdown voltage) was significantly reduced by cleaning the ZnSe surface in saturated bromine water (SBW) solution, which was found to be due to removal of the native oxide layr grown on the ZnSe surface. An addition of a small amount of Cd to the W contact reduced the V_T values of the W contacts from about 11 to 6 V.The microstructural analysis indicated the formation of the Cd_XZn_<1-x>Se layrs at the metal/ZnSe interface with Cd composition (x) larger than 0.9. From the present experiment, it was concluded that formation of the thin large-area Cd_xZn_<1-x>Se layrs is crucial to reduce the V_T value to nearly zero by the conventional DA technique.