TEMPERATURE AND FLOW MODULATION DOPING OF MANGANESE IN ZNS ELECTROLUMINESCENT FILMS BY LOW-PRESSURE METALORGANIC CHEMICAL-VAPOR-DEPOSITION

A temperature and flow modulation (TFM) technique has been developed t o modulate the manganese doping profile in ZnS phosphor material grown by low-pressure metalorganic chemical vapor deposition for alternatin g-current thin film electroluminescent devices (TFELDs). In the TFM te chnique, modulation of both the substrate temperature as well as the f lows of metalorganic sources, diethylzinc and tricarbonyl-(methylcyclo pentadienyl)-manganese (TCPMn), was used to grow a structure consistin g of alternating layers of undoped ZnS at 400-degrees-C and Mn-doped Z nS where Mn being incorporated into the undoped ZnS at 550-degrees-C. X-ray results indicated that MnS(x) phases were present within the ZnS host crystal matrix for the modulation doped samples, while a MnxZn1- xS solid solution was present in the uniformly doped samples. The lumi nescence efficiency of the TFELDs could be modified by growing the pho sphor with dopant (luminescent center) modulation. The TFELDs with a s ingle modulated doping phosphor layer showed lower threshold voltages in the range 70 to 80 V with light emission in the 580 to 587 nm wavel ength range. With a twofold increase in the total thickness of the und oped ZnS layer, the brightness and the luminescence efficiency, measur ed at the threshold voltage plus 40 V, increased by a factor of 20 and 10, respectively. The electroluminescent (EL) characteristics of the phosphors with multiple dopant layers showed higher luminescence effic iency. By using the TFM growth technique, one can engineer the lumines cent center distribution in the phosphor layer to improve the EL chara cteristics.