The photoluminescence （PL） and Raman spectra of undoped ZnO films deposited directly on Si substrate （sample A）,on Si substrate through a SiC buffer layer （sample B）,and on a ZnO crystal wafer （sample C） are investigated. There are emission peaks centered at 3.18eV （ultraviolet,UV） and 2.38eV （green） in these sampies. Comparing the Raman spectra and the variation of the PL peak intensities with annealing atmosphere, we conclude that the luminescence of the samples is related to the tensile strain in the ZnO film due to the lattice mismatch between the film and the substrate. In particular, the tensile strain reduces the formation energy of OZn antisite oxygen defects,which generate the green emission center. After annealing in oxygen-rich atmosphere, many OZn defects are generated. Thus, the intensity of green emission in ZnO/Si hetero-structure materials increases due to tensile strain in ZnO films.
The fabrication and characterization of a Schottky-emitter heterojunction-collector UV-enhanced bipolar phototransistor （SHBT） are presented. The luminescence peak of the ZnO film is observed at 371nm in the PL spectrum. The sensitivity of the ultraviolet response from 200 to 400nm is enhanced noticeably, and the spectrum response at wavelengths longer than 400nm is also retained, The experiments show that the Au/n-ZnO/p-Si SHBT UV enhanced phototransistor enhances the sensitivity of the ultraviolet response noticeably. The UV response sensitivity at 370nm of the phototransistor is 5-10 times that of a ZnO/Si heterojunction UV enhanced photodiode.
利用低压金属有机化学气相淀积(LP MOCVD)在Si基片上外延生长ZnO薄膜,制备了两类样品一类是在Si上直接外延ZnO,另一类是在Si上通过SiC过渡层来外延ZnO.根据两类样品的拉曼光谱、x射线衍射、原子力显微图和光致发光的结果,表明ZnO外延薄膜中的张应力对薄膜的结晶状况有着重要的影响,使用SiC过渡层能够有效缓解ZnO薄膜中的张应力,减小缺陷浓度,提高ZnO外延层的质量;然后根据缺陷的形成机制进一步提出,对于ZnO Si,其中较大的张应力导致了高浓度的非辐射复合缺陷的形成,使得样品的紫外和绿峰的发射强度均大大降低;对于ZnO SiC Si,其中较小的张应力导致ZnO薄膜中主要形成氧替位缺陷OZn,从而使发光中的绿峰增强.
