Gallium phosphide monolithic display with low drive power

A gallium phosphide monolithic numeric display with seven segments has been developed by a mesa-etching technique. Internal absorption of red emission is small so that optical isolation is very difficult in monolithic-type displays. This obstacle has been overcome by sufficiently deep mesa-etching in hot aqua regia, using a stable SiO2film as a mask. Luminance and optical isolation of segments are found to be largely dependent on the configuration of the rear contacts and have been much improved by the effective combination of a highly reflective contact and an absorbing contact. Completed devices with a digit size of 3.1 mm high and 1.7 mm wide are operated at only 10 mA per digit with a luminance of 100 fL. The ratio of the luminance of the excited and unexcited segments is as high as 85:1 in the dark.