Dependence of Electrical Properties on Work Functions of Metals Contacting to p-type ZnSe

In order to search a possibility to prepare Ohmic contacts to p-ZnSe by depositing a single metal element, the electrical properties and thermal stability were studied by a current–voltage (I–V) method for a variety of metals (In, Cd, Nb, W, Cu, Ag, Au, Ni, Pt, and Se) contacting to nitrogen-doped ZnSe layers grown by the molecular beam epitaxy technique. All the metals were deposited on the ZnSe substrates which were chemically cleaned prior to metal deposition in order to remove the native oxide layers. The turn-on voltages (V T) and differential resistances were determined by the I–V curves for these contacts before and after annealing. The contacts were divided into three groups by the V T values: (1) In, Cd, Nb, and W contacts with V T∼16 V, (2) Au and Pt contacts with V T larger than 9 V, and (3) Cu, Ag, Ni, and Se contacts with V T∼3 V. The lowest V T value of 2 V was achieved by the Cu contact. However, this Cu contact deteriorated during storage at ambient temperature. The V T value of ∼3 V was routinely obtained for the Ag and Ni contacts. The Ni contact is the most promising materials for the device application among the contact materials studied in the present experiment, although the linear relation in the I–V behavior was not obtained. The electrical properties of these contacts during annealing at temperatures below 300° C were studied, and no significant reduction of the V T value was obtained in the present contacts. The present study suggests that the deposition of a single metal element to p-ZnSe with doping level of 1×1018 cm-3 would not provide low resistance Ohmic contact.