MBE growth and characterization of hexagonal ZnCdMgSe layers and ZnCdSe/ZnCdMgSe QW structures on GaAs (111) substrates

Abstract

ZnCdMgSe epilayers and ZnCdSe/ZnCdMgSe quantum well structures were grown on GaAs(111)A and B substrates by MBE using a low-temperature-grown CdS buffer layer. X-ray reciprocal space maps demonstrated that ZnCdMgSe epilayers grown on CdS buffer layers were predominantly hexagonal structures. In the quantum well structures, in-situ RHEED pattern also demonstrated the hexagonal structure during the growth. X-ray diffraction results showed that the crystalline quality of the ZnCdMgSe epilayers grown on GaAs(111)A surface was much better than that on the (111)B surface. Low temperature photoluminescence of ZnCdMgSe epilayers were dominated by the deep and shallow donor-acceptor pair emissions for the case of GaAs(111)A and B, respectively. The peak energy positions of the photoluminescence spectra increased with increasing the growth temperature. Although strong emissions from ZnCdMgSe barriers were observed, emissions from the ZnCdSe QW structure were very weak. IntroductionThe II-VI compound-based materials system is still one of the best choices for the green light emitting devices especially for laser diodes (LDs) even when considering the nitride materials system. However, the lifetime of LDs fabricated by II-VI compounds has been short and limited by the generation and propagation of extended defects [1]. Since hexagonal wurtzite structures have lower symmetry and fewer gliding planes than cubic zincblende structures, the dislocation should not move easily [2] and should be confined to lattice planes parallel to the interface between epilayers and substrates in hexagonal structures [3]. Therefore, hexagonal II-VI compound-based materials may be a plausible candidate to realize long-lifetime LDs [4] 1 . Until now, we have grown hexagonal ZnCdSe epilayers on GaAs(111) substrates by molecular beam epitaxy (MBE) for the green light emitting device applications, and reported that the cubic phase was incorporated into the hexagonal epilayers [5]. However, if the hexagonal phase purity of ZnCdSe epilayers can be improved, a hexagonal ZnCdSe/ZnCdMgSe quantum well (QW) structure becomes one of the suitable green LD structures.Therefore, we improved the hexagonal phase purity of ZnCdSe epilayers by insertion of a lowtemperature-grown (LT) CdS buffer layer, and carried out MBE growth and characterization of hexagonal ZnCdMgSe epilayers with the LT-CdS buffer layer on GaAs(111)A and B substrates. The reason why we used GaAs(111)A and B substrates is that we investigated how the polarity of the substrates affects structural and optical properties of ZnCdMgSe epilayers. Furthermore, we fabricated hexagonal

Two-dimensional X-ray diffraction characterization of (Zn,Cd,Mg)Se wurtzite layers grown on Bi2Se3

“…Wurtzite structures possess desirable properties that are different from their zinc-blend counterparts such as fewer glide planes and a polar band structure that may prove advantageous for some device applications. The possibility of intentionally stabilizing and optimizing the wurtzite phase of the II-VI overlayers by the appropriate choice of growth conditions 10 is under investigation in our laboratory.…”

“…To achieve this goal, pole figures were obtained for several cubic and hexagonal planes of the (Zn,Cd,Mg)Se family. The results displayed the presence of a predominant wurtzite phase through the observation of the (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and (10)(11)(12)(13) planes, showing their 2 value and six poles at the corresponding  positions. On the other hand, there was no evidence of the cubic (220) and (311) planes: neither a peak at the appropriate 2 values, nor the corresponding poles at  positions were observed for those two planes.…”

“…Also, one broad peak is observed between 45 o and 50 o . Over this wide range an ambiguity arises between (220) and(10)(11)(12)(13) of ZnSe due to their proximal 2 values of 45.2 o and 49.5 o , respectively. The pole figure made over this 2 range shows six poles with about equal intensity, which suggests we are in the presence of a hexagonal system rather than a cubic system.…”