1, Arizona State University, Tempe, Arizona, United States
It is a common problem that growing a given composition in a desired morphology is not always possible and thus limiting the application gamut. In this research, we have demonstrated dual ion exchange processes to grow novel optoelectronic structures that are unlikely to be grown directly. In the literature, separate anion or cation exchange has been demonstrated before, but to the best of our knowledge dual ion exchange processes where both anion and cations are partially replaced has been systematically demonstrated for the first time with this research. The scope of this study is to grow any composition of ZnCdSSe quaternary alloys in nanosheet form. It is demonstrated that growing CdS- and CdSe-rich quaternary ZnCdSSe alloys in nanosheet form is easy, but due to very low vapor pressure of wide bandgap materials such as ZnSe and especially ZnS it is almost impossible. The reason is that only VLS mechanism is active under the low vapor pressure and thus leading to grow those materials in 1D nanowire form. On the other hand, materials in Cd, S and Se-rich are easily grown in 2D nanosheet morphologies and therefore they provide a good platform for the morphology transfer process. Here, we have used CdSe-rich materials as a basis and dual ion exchange process was implemented on those materials in a temperature region higher than the one used to grow CdSe nanosheets. As a result of this process we have grown ZnS- and ZnSe-rich ZnCdSSe quaternary alloys in nanosheet form and this paved the way for variety of optoelectronic applications such as white laser, personalized light emitters, full color photodetectors, and so on. This mechanism is not only applicable for ZnCdSSe, but also for any other material systems in which the desired morphology and composition combinations cannot be obtained directly.