PERFEZIONAMENTO NEI DIODI EMETTI TORI DI LUCE PER IL FUNZIONAMENTO A BASSA TEMPERATURA E A BASSA TENSIONE

摘要

1454085 Luminescent materials and uses thereof MINNESOTA MINING & MFG CO 11 Oct 1973 [12 Oct 1972 10 Sept 1973] 47612/73 Heading C4S [Also in Division H1] An L.E.D. comprises a single crystal of ZnO which exhibits a fluorescent efficiency of not less than 0.001 in a band between 3700Š and 4000Š at 77‹ K., and includes a substantially ohmic cathode 36 and a rectifying anode 34, the diode emitting violet light at room temperature. The cathode may be of low work function In, or Zn or tin oxide and/or indium oxide and preferably of work function # the work function of ZnO. The anode may be high work Cu, Ag, Au, Pt or C and ultra-violet responsive phosphor 30 may convert the L.E.D. emission. Jig 38 facilitates contact formation. Fig. 4 (not shown) is a coherent radiation source with reflector layers (60), (62), and Au anode (64). Mechanisms are discussed including decay of free excitons, and donors are provided to compensate acceptor concentration of <10 p.p.m. by heating in the presence of ZnS for example for Zn diffusion, followed by quenching. Crystals may be thin slabs from a single crystal or naturally grown and selected by laser or Hg arc excitation according to efficiency. Operation may be A.C. or D.C., the resistivity may be 1 # cm. for 1017 electrons/c.c. and reduction of acceptor states provided by Li and Na and in amount <1016/c.c. is disclosed. Crystal orientation is discussed and surfaces preferably shaped to minimize internal reflection and to focus. Green fluorescence of as grown ZnO may be countered by excess Zn doping and removal of an outer layer. Detailed examples specify voltages and current densities, band gaps, dimensions and further electrode details, including as examples only, a plurality of point contacts provided by Au particles in silicate binder, Au needles with blue ZnS phosphor on the opposite crystal face, four anode dots, gold paste over a blue organic phosphor on the oxygen face, the same phosphor on the opposite face increasing brightness, Au coated silica, rough 10Á Au spheres, and cleaved or otherwise mechanically deformed evaporated films. Applications are specified. Reference is included to Specification 1,452,515.