Rectifying Structures Resulting from Gold, Cadmium and Thallium Deposited on Selenium

Abstract

ABSTRACTStructures of the form Al-Bi-Se-metal were fabricated by deposition of the metals gold, cadmium, bismuth and thallium as thin films on a layer of crystallized selenium. The selenium was itself evaporated on a layer of bismuth on an aluminum base. This Al-Bi-Se base contact was rendered ohmic by substrate heating during the selenium deposition. The diodes showed forward-to-reverse current rectification ratios ranging from large for thallium to small for gold. At small forward voltage, the current density increased with increasing work function from thallium to gold, whereas the voltage intercepts Vo on plots of (capacitance)−2 versus reverse voltage decreased with increasing work function. From these Vo values and the slopes of the latter plots, barrier heights were deduced and plotted against work function. From this plot showing a decrease of barrier height with decreasing work function, it was possible to estimate an interface state density of 1013 cm−2 volt−1 assuming the existence of an interfacial layer 100Å in thickness. While the Se-Tl contact showed excellent rectification, it exhibited rapid degradation with time from atmospheric oxidation.