Development of Pure Green LEDs Based on ZnTe

Abstract

Based on high quality ZnTe substrates and a simple thermal diffusion process, pure green light-emitting diodes (LEDs) were first realized reproducibly, overcoming the well-known compensation effect specific to II–VI materials. This success is due to the use of high quality p-type ZnTe single crystals with low dislocation densities of the level of 2000 cm—2 grown by the vertical gradient freezing (VGF) method and the suppression of compensating point defects by low temperature annealing with covering the substrate surface by the deposition of n-type dopant, Al. PL measurement proved that the present ZnTe single crystals are high quality materials with highly resolved spectra. The stoichiometry control by wafer annealing was also studied systematically. The thermal diffusion coefficient and the activation energy of Al were determined from the pn interface observed by scanning electron spectroscopy (SEM). The formation of the intrinsic pn junctions was confirmed from the electron-beam induced current (EBIC) observation and I–V measurement. The bright 557 nm electroluminescence (EL) from these pn junctions was reproducibly observed under room light at room temperature, with the lifetime exceeding 1000 h.