无催化法制备ZnO纳米针的结构及光学特性

Structural and Optical Properties of ZnO Nanoneedle Grown by Catalyst-free Synthesis

采用无催化脉冲激光沉积(PLD)方法,在InP(100)衬底上生长纳米ZnO针状结构。采用扫描电子显微镜(SEM)、X射线衍射(XRD)以及光致发光(PL)谱等对ZnO纳米针的形貌、晶体结构和光学特性表征。SEM图像观察到ZnO纳米针状结构具有一定的取向性。XRD测试在2θ=34.50°处观测到强烈的ZnO(002)衍射峰,证实ZnO纳米针具有较好的c轴择优取向。室温PL谱在379nm处观察到了较强的自由激子发射峰(半峰全宽为13.5nm),而微弱的深能级跃迁峰位于484nm,二者峰强比值为11∶1,表明生长的纳米ZnO结构具有较高的光学质量。

In recent years, semiconductor nanostructures have attracted much attention due to their potential application in a wide range of advanced devices. ZnO nanostructure has become a promising candidate for applications in functional oxide-based, blue-ultraviolet light emitting, field-effect transistor and transparent conductivity, because of its large direct wide band gap of 3.37 eV and large exciton binding energy of 60 meV. Furthermore, ZnO nanostructure can be used for electromechanical coupled sensor, transducers and biomedical applications. Many researchers reported the synthesis of ZnO nanostructures by a vapor-liquid-solid （VLS） mechanism. This approach is the most widely used technique for synthesizing aligned ZnO nanostruclyst-free sapphire structure growth techniques of ZnO nanostructures. Most of the related works were focused on the silicon and substrates using VLS technique, however there was no report of catalyst-free fabricating ZnO nano- on InP using pulsed laser deposition （PLD） technique. In this paper, we employed InP wafers as the substrates, a undoped thin ZnO film with thickness of 20-30 nm was predeposited on InP substrate surface by PLD as the buffer layer. The predeposited ZnO film assembled uniform ZnO islands on the InP substrate surface. ZnO nanoneedle-type nanostructure were success- fully synthesized on indium phosphide （InP） （100） substrates. It illuminates that the using of catalyst is not absolutely necessary in the growth of ZnO nanostructures. The morphologic, crystal structural and optical properties were characterized with scanning electron microscopy （SEM）, X-ray diffraction （XRD） and photolu- minescence （PL） spectrum analytic approaches, respectively. SEM pattern showed that the ZnO nanoneedle was obtained in high yield and high-quality and had a preferential growth orientation that was perpendicular to the substrate surface and are well separated from each other. From the XRD scan results, a strong diffraction peak was observed at 34.5°, attributing to the ZnO （002） plane, indicating that the growth direction is welloriented along c-axis and has highly crystalline quality. A typical PL spectrum, measured at room tempera- ture, showed a strong free-excition emission at 379 nm with a full width at half maximum （FWHM） value of 13.5 nm, and a weak deep level （DL） emission at 484 nm, the intensity ratio of free-excition emission relative to DL emission was 11：1, indicating that the ZnO nanoneedles produced in this experiment are of high optical quality. The simple and efficient method to fabricate ZnO nanoneedle has the following advantages： low cost, potential for wafer-scale production, and guaranteeing high-purity of ZnO. Therefore, this method may benefit in the applications for nano-devices.