硼掺杂对单晶金刚石薄膜结构及生长的影响

Microstructure and Growth of Epitaxial Single Diamond Films with Boron-Doping

采用自制的环形谐振腔式微波等离子体化学气相沉积(MPCVD)设备,在其他工艺参数不变的情况下,通过改变反应气中掺杂源硼烷的浓度,制备不同掺硼量的外延单晶金刚石薄膜。通过激光拉曼光谱(Raman)、激光荧光发射光谱(PL)以及X射线衍射(XRD)摇摆曲线等测试手段对外延金刚石薄膜的微观结构进行分析,结果表明,在325 nm波长的激光激发下,外延金刚石薄膜在524 nm处产生了与硼相关的荧光峰位,且随气源中硼烷浓度增加,荧光峰(524 nm)峰强增大,拉曼特征峰和XRD摇摆曲线特征峰半高宽(FWHM)都呈增加趋势,说明随着硼烷浓度增加,金刚石薄膜中硼含量增加,晶体结构的完整性逐渐降低,外延薄膜的质量变差。通过光学显微镜(OM)、原子力显微镜(AFM)对外延单晶金刚石薄膜的表面生长形貌进行分析,结果表明,随着气源中硼烷浓度增加,薄膜表面的台阶流生长模式没改变,但台阶流的台阶数量逐渐减少,台面宽度台面高度逐渐增加,说明随着硼烷浓度增加,台阶流生长状态改变。因此,硼掺杂变化将导致外延单晶金刚石膜的结构及生长特征发生显著改变。

Using a self-made ring-type resonator microwave plasma chemical vapor deposition( MPCVD) system,the epitaxial single diamond films with different boron content was prepared by changing the concentration of borane in the reaction gas while other process parameters maintained constant. Then the microstructure of the obtained films was investigated by Raman spectroscopy,laser fluorescence emission spectroscopy and X-ray diffraction( XRD) rocking curve. The results showed through 325 nm wavelength laser exciting,the films produced a fluorescence peak at 524 nm associated with boron doping,and along with the increase of borane concentration in the reaction gas,the intensity of fluorescence peak and the full width at half maxima( FWHM) of characteristic peaks of Raman spectroscopy as well as XRD rocking curve would also increase,which indicated that the enhancement of borane concentration in the reaction gas would give rise to the boron content in the epitaxial single diamond film and at the same time,the crystal structure integrity and quality would decay gradually. Finally the surface morphologies of the epitaxial single crystal diamond films were analyzed by optical microscope( OM) and atomic force microscope( AFM),which predicted that all films grew in the step flow pattern,but as the borane concentration in reaction became bigger,the number of the steps would decrease and its height and width increased gradually.Therefore,boron-doping would result in significant changes in the microstructure and growth characteristics of epitaxial single crystal diamond films.