根據掃描式電子顯微鏡的觀察、模擬軟體的分析、X光繞射儀以及拉曼光譜的量測，我們發現: 鎂摻雜量較少的樣本，展現較小的伸張應力，以及較佳的晶格品質因此具備較高的內部量子效率。;In this study, the effect of lattice strain before and after substrate transfer on the optoelectrionic properties of nanostructured InGaN quantum wells (QWs) structures was investigated. The nanostructure QWs were grown on (100) Si substrates by metal-organic chemical vapor deposition (MOCVD), employing ZnO nanorods as the buffer layer to release the huge stratin between Si and the nitride epilayer.
Using the small lattice mismatch between ZnO and GaN, we successfully grew the (10-11) semi-polar nanopyramidal QWs on the (100) Si substrate. The diffusion of Zn into GaN during the epitaxial growth also allows us to achieve the naturally formed p-type GaN, producing the desired p-side-down structure for QWs with enhanced interal quantum efficiency. During the growth, three different flow rates of Bis(cyclopentadienyl)-magnesium Mg(C5H5)2, i.e. 40, 80, and 120 sccm were adopted with the attempt to study the effect of p-type doping on the strain and the quantum efficiency of the QWs.
Due to the large thermal mismatch between the GaN epilayer and the Si substrate, huge lattice strain is expected in the epilayer after the MOCVD growth. The strain decreased the internal quantum efficiency of the InGaN QWs via the quantum-confinement Stark effect. The semipolar nanostructured QWs produced in this study are expected to exhibit improved radiative recombination efficiency becoause of the alleived QCSE. In addition, we transferred the epitaxial layer from the Si substrate to a silver substrate using a wet-etching technique, releasing the stress on the samples and increasing reflectivity at the epilayer/substrate interface. The released stress and enhanced interface reflectivity should lead to improved external quantum efficiency of the nanopyramidal QWs.
Scanning electron microscopy was used to observe the microstructure of the samples and a simulation software is used to analyze the relationship between the film thickness and the reflection wavelength. The samples were also characterized by x-ray diffraction (XRD) and Raman spectroscopy. According to these characterizations, it is found that the sample with less magnesium doping exhibits less tensile stress, and thus the higher internal quantum efficiency.
