Influence of unintentional doped carbon on growth and properties of N-doped ZnO films

Abstract

The evolution of optical and electrical properties induced by rapid thermal annealing is studied on nitrogen-doped ZnO samples grown by metal-organic chemical vapor deposition (MOCVD). Correspondingly, in the Raman spectra carbon cluster related D and G modes have been observed to increase with annealing temperature. The increase in the intensity ratio of D and G modes indicates growing of carbon clusters, revealing an interesting change in unintentional doped carbon, which is a popular impurity in MOCVD grown N-doped ZnO. Substitutional or interstitial carbons in the grains may migrate to grain boundaries to incorporate with some existing carbon clusters to form larger ones. Accordingly, zinc vacancies will then be easily formed as annealing temperature increased, resulting in eminent green band emission at room temperature photoluminescence. The band edge emissions also show significant changes with several shoulders observed by thermal annealing, which can be ascribed to acceptor or donor related emissions. The changes in emissions agree well with the evolution of the electrical property of annealed samples. This study shows that unintentional doped carbon has a great influence on ZnO growth by forming clusters in the grain boundary area and also on the optical and electrical properties by forming C related defects in the grains.