Development of pure green LEDs based on ZnTe

Based on high quality ZnTe substrates and a simple thermal diffusion proces s, 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 crystal s with low dislocation densities of the level of 2000 cm(-2) grown by the v ertical gradient freezing (VGF) method and the suppression of compensating point defects by low temperature annealing with covering the substrate surf ace by the deposition of n-type dopant, Al. PL measurement proved that the present ZnTe single crystals are high quality materials with highly resolve d spectra. The stoichiometry control by wafer annealing was also studied sy stematically. The thermal diffusion coefficient and the activation energy o f Al were determined from the pn interface observed by scanning electron sp ectroscopy (SEM). The formation of the intrinsic pn junctions was confirmed from the electron-beam induced current (EBIC) observation and I-V measurem ent. The bright 557 nm electroluminescence (EL) from these pn junctions was reproducibly observed under room light at room temperature, with the lifet ime exceeding 1000 h.