ZnMgSe/ZnCdSe and ZnMgSe/ZnSeTe distributed Bragg reflectors grown by molecular beam epitaxy

This article investigates distributed Bragg reflectors (DBRs) based on two wide-gap II–VI semiconductor alloy combinations: ZnMgSe/ZnCdSe and ZnMgSe/ZnSeTe. Prior to fabrication of the DBRs, a prism coupler technique was used to determine the indices of refraction n of the above ternary alloys of various compositions prepared by molecular beam epitaxy (MBE). Using these values of n, two DBR systems, ${\mathrm{Zn}}_{\mathrm{0.66}}{\mathrm{Mg}}_{\mathrm{0.34}}{\mathrm{Se/Zn}}_{\mathrm{0.74}}{\mathrm{Cd}}_{\mathrm{0.20}}\mathrm{Se}$ and ${\mathrm{Zn}}_{\mathrm{0.62}}{\mathrm{Mg}}_{\mathrm{0.38}}{\mathrm{Se/ZnSe}}_{\mathrm{0.56}}{\mathrm{Te}}_{\mathrm{0.44}},$ were fabricated, each with a relatively large difference in the indices of refraction between its layer materials. It was found that although a higher reflectivity could be achieved using the ZnMgSe/ZnSeTe combination (since it manifests a larger difference in their indices of refraction $\text{Δn=0.35),}$ the number of periods which can be deposited in this DBR system is limited due to growth difficulties that arise when combining ZnMgSe and ZnSeTe. Therefore the ZnMgSe/ZnSeTe DBR system, which was restricted to just 10 periods, yielded a modest reflectivity of 85%. On the other hand, although $\mathrm{\Delta n}$ in the ZnMgSe/ZnCdSe DBR system is smaller $\text{(Δn=0.20),}$ it poses fewer growth difficulties, making it possible to grow DBR stacks consisting of a large number of layers without compromising the crystal quality of the structure. By growing 20 periods of the ZnMgSe/ZnCdSe DBR system, we obtained a DBR with a reflectivity as high as 98%.