衬底温度对ZnO薄膜的结构和光学特性的影响

Substrates Temperature Influence on the Structural and Opticcal Properties of ZnO Films

利用等离子体辅助分子束外延(P-MBE)设备在蓝宝石衬底上通过改变生长温度,制备了不同的ZnO样品。研究了衬底温度对ZnO的结构、光学和电学性质的影响。样品的晶体结构利用X射线衍射谱进行表征。X射线衍射谱表明,所有的ZnO样品都是(002)取向的六角纤锌矿结构。随着生长温度的升高,X射线的(002)衍射峰的半峰全宽逐渐减小。样品的表面形貌随着衬底的温度改变而变化,在800℃得知了平整的ZnO表面。通过光致发光的实验得知,ZnO的紫外发光随着生长温度的升高,强度逐渐增强。光致发光的来源为ZnO的自由激子发光。在生长温度为800℃时,得到了高质量的ZnO单晶薄膜,X射线衍射峰的最大半峰全宽为0.05°,霍尔迁移率为51 cm2/(V.s),载流子浓度为1.8×1018cm-3。

The ZnO films grown with different growth temperature have been deposited on c-Al2O3 substrates by plasma assistant molecular beam epitaxy（P-MBE）.Their crystal structures are characterized by X-ray diffraction（XRD）.The XRD results indicate that all the ZnO films with the（002） preference orientation of hexagonal wurtzite structure.The full width at half maximum（FWHM） of the（002） diffraction peak decreases as the growth temperature increasing.The surface morphology of the ZnO films is measured by scanning electron microscope（SEM）,the surface morphology of the ZnO films grown at different growth temperature changes gradually.In the SEM image of the film grown at 500 ℃,there are a large number of particles,and the surface of the film is rough.The particle size is about 50~100 nm.The particle size increases（about 100~200 nm） at 600 ℃ growth,which indicates that the particle size increase with the increasing of the growth temperature.As the film growth temperature reaches 700 and 800 ℃,it can be found that the surface of the film become uniform and smooth from the SEM image.The photoluminescence（PL） intensity of the ZnO film increased with the increasing of the growth temperature.The origin of the PL peak is the free exciton emission.The carrier concentration and Hall mobility of the films as a function of growth temperature are studied.Hall measurements show that all the films are n-type.The carrier concentration value decreases gradually from 3.4×1018 cm-3 to a value of 1.8×1018 cm-3 with increasing the growth temperature from 500 to 800 ℃.The Hall mobility of ZnO films rises from 11 cm2/（V·s） to 51 cm2/（V·s） with the increase of film growth temperature.The high quality ZnO thin films was obtained at 800 ℃,exhibiting that the FWHM of XRD is about 0.05°,the Hall mobility is about 51 cm2/（V·s）,the carrier concentration is about 1.8×1018 cm-3.