Molecular beam epitaxy growth and characterization of beryllium-based II-VI semiconductor materials and distributed Bragg reflectors for potential application in visible light emitters

This thesis describes the molecular beam epitaxy (MBE) growth and characterization of Zn_xCd_yMg_1−x−ySe-based distributed Bragg reflectors (DBRs) and new Be_xZn_yCd_1−x−y Se and Be_xZn_1−xTe material systems on InP substrates. DBRs can be integrated with Zn_xCd_yMg _1−x−ySe-based light emitting diodes (LEDs) to fabricate resonant cavity LEDs (RCLEDs) that have better spectral purity and higher emission intensity than the conventional LEDs. The Be_xZn_y Cd_1−x−ySe alloy can be used as an active layer and the Be_xZn_1−xTe alloy can be used as a p-type contact layer in Zn_xCd_yMg_1−x−ySe-based LEDs. Application of these materials is proposed to improve reliability as well as the optical and electrical properties of light emitters.; DBRs with different numbers of periods and different layer composition were grown by MBE from Zn_xCd_yMg_1−x−y Se-based materials on InP substrates. Their reflectivity maxima were controlled by the individual thicknesses of constituent layers, and were adjusted in the range of 615–500 nm, covering the red, green, and blue-green regions of the visible spectrum. A maximum reflectivity of 95.5% was obtained for a DBR with 16 periods. Electrical properties of chlorine-doped n-type ZnCdSe/ZnCdMgSe DBR structures were also investigated and high carrier concentration was achieved in the constituent layers. These results demonstrate that Zn _xCd_yMg_1−x−ySe is a promising material system for the design of highly reflective, conductive DBRs for application in high efficiency RCLEDs.; Be_xZn_yCd_1−x−ySe epilayers and Be_0.08Cd_0.92Se/Zn_0.32Cd_0.25Mg _0.43Se quantum well (QW) structures were grown and investigated. Their high crystalline quality was established using X-ray diffraction measurements. Efficient excitonic emission was observed both from the Be_xZn _yCd_1−x−ySe epilayers and the QWs. Based on these results and on the expected lattice hardening properties of BeSe, we propose that Be_xZn_yCd_1−x−ySe is an attractive QW material for light emitters.; The growth and optical properties of a set of Be_xZn_1−x Te epilayers were studied. Comparison of the reflectivity and the photoluminescence spectra allowed us to locate the direct-to-indirect band gap crossover for this alloy at x ≈ 0.28. Our results indicated that Be_0.48Zn _0.52Te, which is the composition that is lattice matched to InP, is an indirect semiconductor with a Γ → X indirect band gap of 2.77 eV, and a Γ → Γ direct band gap of 3.14 eV. Therefore, it is transparent for the visible light and can be used as a top p-type contact layer in LEDs.