高Al组分AlGaN的MBE生长及表面活性机理

MBE Growth and Surface Activity Mechanism of High Al-Component AlGaN

采用分子束外延(MBE)方法制备了高质量的高Al组分AlGaN薄膜,在室温下获得了266 nm波长的深紫外发光。利用原位监控系统,结合原子力显微镜(AFM)和变温光致发光(PL)谱研究了生长前端的Ga原子的表面活性作用对AlGaN薄膜的生长模式、表面形貌和光学性质的影响,并通过二次离子质谱仪(SIMS)探究了生长温度与p型AlGaN Mg掺杂浓度的变化关系及内在机理。结果显示,Ga原子不仅参与AlGaN的结晶,而且在薄膜生长和Mg掺杂中发挥着表面活性剂的作用,能够促进Al原子的迁移与并入。Ga原子作为表面活性剂有利于AlGaN薄膜进行二维层状生长,改善AlGaN薄膜的表面形貌和光学特性;它还能够提高Al原子的并入效率,使AlGaN薄膜具有更短的发光波长。此外,适当降低p型AlGaN薄膜的生长温度,能减少Mg原子脱吸附并增强Ga原子的表面活性剂作用,从而提高Mg的掺杂浓度。

High quality and high Al-component AlGaN films were prepared by molecular beam epitaxy(MBE)method,and the deep ultraviolet emission at a wavelength of 266 nm at room temperature was obtained.The surfactant effect of Ga atoms at AlGaN growth front on the growth mode,surface morphology and optical properties of AlGaN films were investigated by using the in-situ monitoring system,atomic force microscope(AFM)and temperature-dependent photoluminescence(PL)spectrum.And the relation between the growth temperature and Mg-doping concentration of p-type AlGaN and its internal mechanism were explored by using secondary ion mass spectrometer(SIMS).It is revealed that Ga atoms not only participate in the crystallization of AlGaN,but also play the role of surfactant in enhancing the mobility and incorporation of Al atoms during the film growth and Mgdoping.As a surfactant,Ga is beneficial to the two-dimensional layered growth of AlGaN films,and then improves the surface morphologies and optical properties of AlGaN films.It also can improve the incorporation efficiency of Al atoms and make AlGaN films have shorter light-emitting wavelength.Furthermore,Mg-doping concentration can be increased by appropriately decreasing the growth temperature of p-type AlGaN films,because lower temperature can reduce the desorption of Mg atoms and enhance the effect of Ga as a surfactant.