II-VI semiconductors on InP for green-yellow emitters

Novel II-VI compound materials such as MgZnCdSe, BeZnCdSe, BeZnTe, and related superlattices grown on InP substrates have been investigated for yellow-green emitters employing molecular beam epitaxy. MgZnCdSe was grown in the Mg composition range of 0∼0.6 to clarify the compositional dependency of the bandgap and refractive index. MgSe-ZnCdSe and MgSe-ZnSeTe short-period superlattices were investigated; the superlattices behaved as quasi-quaternaries (QQs), so that their bandgap energies were controlled by the layer thickness combination of superlattices. For realizing strong lattice hardness, Be-contained H-VI compounds, such as BeZnCdSe and BeZnTe bulk crystals, and MgSe-BeZnCdSe, ZnCdSe-BeZnTe, and MgSe-BeZnTe short-period superlattices were investigated. The superlattices also behaved with QQ properties, by use of which multilayered heterostructures could be grown without growth interruption. Applying the superlattices, visible LEDs were fabricated emitting at the wavelengths from 554 (yellow-green) to 644 nm (red) at room temperature. For yellow (575 nm) LEDs, a long lifetime more than 3500 h was demonstrated even for defect densities as high as 10⁵ cm^-2. The BeZnTe buffers were effective in suppressing the defect density to less than 7 × 10³ cm^-3. Finally, MgZnCdSe-based II-VI LDs were successfully operated with yellow-green lasing emissions around 560 nm at 77 K.