高质量ZnO及BeZnO薄膜的发光性质

用分子束外延设备插入缓冲层在c面蓝宝石上生长得到高质量ZnO和BeZnO薄膜。XRD测试显示薄膜具有六方结构和c轴取向,并具有良好的晶体质量,其中ZnO薄膜的半高宽仅为108 arcsec,Be_xZn_1-xO薄膜的半高宽小于600 arcsec。对ZnO和BeZnO薄膜的拉曼光谱进行对比研究发现,随着Be元素的掺入,A₁(LO)、A₁(2LO)声子模频率往大波数方向移动,并且首次发现了与Be元素掺杂有关的局域振动模。利用变温光致发光光谱研究了薄膜的发光性质,结果显示ZnO薄膜室温光致发光只出现一个紫外发发光峰(378 nm),而低温光谱(80 K)则出现了很强的自由激子发光峰。随着温度的升高,束缚激子发光逐渐湮灭向自由激子发光转变,并且峰值位置红移。相对于ZnO薄膜,BeZnO薄膜的紫外发光主峰位置蓝移,并且由于Be元素的掺入导致薄膜晶体质量下降,在低温(80 K)光致发光光谱中没有出现强的自由激子发光峰。另外,在低温光致发光及拉曼光谱中,主峰位置在100~200 K之间有局部最大值,推测为由于合金晶格热膨胀系数失配而引起的应力效应。

Luminescence Characteristics of High-quality ZnO and BeZnO Films

High-quality ZnO and BeZnO films were grown on c-plane sapphire substrate using plasma-assisted molecular beam epitaxy (P-MBE) by inserting metal oxide buffer layers. X-ray diffraction(XRD) results show that all films have hexagonal wurtzite structure and highly c-axis orientation. The full width at half maximum (FWHM) of ZnO film is as low as 108 arcsec,and the FWHM of BeZnO film is less than 600 arcsec. The resonance Raman spectra show that both A₁(LO) and A₁(2LO) phonon modes shift to larger wavenumber with more Be doping. For the first time, the local vibration mode related to Be doping is found. The photoluminescence (PL) spectrum of ZnO films has only one emission peak(378 nm) at room temperature. However, another peak due to the strong free exciton emission is observed at low temperature (80 K). With the temperature increasing, the free exciton emission dominated over the bound exciton emission, and its peak shows gradual red shift. As for BeZnO film, the strong free exciton emission peak is not found at low temperature (80 K) due to the declined crystal quality caused by the incorporation of Be. It is also found that the peak position of BeZnO films in the PL and Raman spectra have local maximum values between 100~200 K, which is suggested to be caused by the stress effect due to the thermal expansion mismatch of the alloy lattices.