Title

OMVPE growth and characterization of ZnSe based materials for blue-green laser applications

Date of Completion

January 1995

Keywords

Engineering, Electronics and Electrical|Physics, Optics|Engineering, Materials Science

Degree

Ph.D.

Abstract

Blue-green light emitting diodes and lasers have been the driving force behind the dramatic improvement in the growth technology of ZnSe based II-VI materials. While blue-green laser diodes grown by molecular beam epitaxy are a reality, OMVPE (organometallic vapor phase epitaxy) grown p-n junction lasers have remained elusive. This study involves the growth of undoped films using a photoassisted low-temperature technique. Also, doping studies were undertaken to achieve n- and p-type ZnSe using chlorine and nitrogen, respectively. A simulation of the ZnSe/ZnTe MQW contacts to p-ZnSe is also reported.^ High temperature ZnSe films grown using dialkyl sources DMZn and DMSe, have been found to exhibit undesirable yellow emissions from self-activated deep levels. A study of an alternate low-temperature, UV light assisted technique for the growth of high optical quality ZnSe films is presented. We have shown an interplay of UV intensity and temperature in determining the optical quality of these layers. A temperature dependent UV intensity threshold, above which specular morphology and suppression of the deep level emissions has been observed. By the use of cadmium doping a further reduction in deep-level yellow emissions is achieved.^ Properties of n-type photoassisted ZnSe films co-doped with Cd and Cl have also been investigated. The samples co-doped with Cd showed increased incorporation of the Cl donors. By the use of Cd co-doping, we have achieved the highest electron concentration yet reported $(2\times10\sp{18}\ \rm cm\sp{-3})$ for HCl doping of OMVPE-grown ZnSe. We propose a model based on the compensation of tetrahedral misfit to explain these results.^ The nitrogen doping of ZnSe to achieve p-type conductivity was studied using tertiarybutyl amine as dopant source. The level of nitrogen incorporation was determined from the structure of the donor-acceptor pair (DAP) emissions in the photoluminescence spectrum. The effects of growth temperature, UV intensity during growth, and dopant flow on the incorporation of nitrogen in ZnSe layers have been investigated. Nitrogen concentrations comparable to MBE-grown ZnSe:N films, were obtained for lower growth temperatures and reduced UV intensities. Most of the ZnSe:N films were highly resistive indicating hydrogen passivation of nitrogen acceptors. ^