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, Zn0.66Mg0.34Se/Zn0.74Cd0.20Se and Zn0.62Mg0.38Se/ZnSe0.56Te0.44, 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 Delta n=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 Delta n in the ZnMgSe/ZnCdSe DBR system is smaller (Delta n=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%. (C) 1999 American Institute of Physics. [S0021-8979(99)04914-2].