GROWTH OF HIGH-QUALITY CUBIC ZNS CRYSTALS AND THEIR APPLICATION TO MIS BLUE LIGHT-EMITTING-DIODES

Cubic ZnS crystals, some 1.5 cm3 in size, have been successfully grown at about 850 ° C using a conventional iodine-transport method. The quality of the crystal obtained can be significantly improved by prebaking the ZnS powder in H2S gas prior to growth. Low-resistive n-type crystals, with a room temperature (RT) resistivity as low as 3 Ω cm, have been characterized by their excitonic and impurity-related photoluminescence emission spectra at 4.2 K. A correlation between the emission properties and surface morphology was found with the various oriented homoepitaxial ZnS layers grown by low-pressure metalorganic chemical vapour deposition (MOCVD). Using the high-quality n-ZnS crystals doped with I donors, an MIS-structured blue LED has been fabricated and yielded an external quantum efficiency as high as 0.05% at RT when a ZnS insulating (I) layer with a thickness of 300 A was deposited on the (110)-oriented ZnS substrate. © 1990, Elsevier Science Publishers B.V. (North-Holland). All rights reserved.