Blue electroluminescence in forward-biased ZnSe diodes
The electroluminescence emission spectrum of forward-biased MIS diodes prepared on high-purity single-crystal ZnSe has been studied over the temperature range 20-290 K. At room temperature the emission consisted of two intense bands in the blue at 4655 and 4770 Å, while at the lowest temperatures much more structure was observed. Thus at 20 K free and bound exciton emission was particularly intense, and the donor-acceptor (DA) pair band emission (the Q series), together with its accompanying free-to-bound series was also prominent. The bound exciton, pair band, and free-to-bound emission were all substantially quenched as the temperature was increased, so that at room temperature the two blue bands were the only remaining components of the luminescence. Evidence is produced to demonstrate that the band at 4655 Å is associated with free exciton recombination following scattering from free electrons in the conduction band. The band at 4770 Å is attributed to free exciton recombination with the emission of two longitudinal optical (LO) phonons.