In Situ Interferometry of MOCVD-Grown ZnO for Nucleation-Layer-Based Optimization and Nanostructure Formation Monitoring

Abstract

A reliable in situ interferometry technique allowed accurate prediction of the change in ZnO morphology during growth on various substrate types. Interferometry results showed that a 40-nm-thick nucleation layer on top of GaN allows growth of smooth and monocrystalline ZnO layers, as also confirmed by x-ray diffractometry (XRD). Studies of ZnO growth on silicon indicated that the surface morphology changes during the high-temperature growth step, resulting in needle-shaped ZnO on top of a thin ZnO initial layer. The observed surface morphology change corresponded to the interferometer signature and allowed identification of nanostructure formation.

Electron field emission from nanostructured semiconductors under photo illumination

“…So far the majority of the device results published in the case of ZnO-based nanostructures [56,57] are based on randomly ordered NWs. Thus, ZnO field-emitter whiskers with nanometer diameter were fabricated by metal-organic chemical vapor deposition (MOCVD) growth on Si substrates (see Figure 9) [28,58,59]. These ZnO field-emitter whiskers have vertically ordered conical nanometer structures and were grown catalyst-free by MOCVD on (100)-Si substrates ( Figure 9).…”

“…The high temperature growth steps took place at 500 • C where the oxygen and DEZ flow were 100 sccm each. The layer features were monitored using a homemade in situ laser interferometer [28,58]. A typical nucleation layer involves a 2-stage growth process where island formation results in reduction of reflectivity, followed by growth of either flat top areas covering the islands or of a planar layer leading to the start of an oscillation.…”

“…The resulting ZnO tips had nanometer size, which is important for high field enhancement and simpler electron emission at smaller bias voltages ( Figure 9). A detailed study of the interferometry of ZnO MOCVD growth and its relevance to nanostructure growth is given by Biethan et al [58]. …”