【作者】 冯超；

【导师】 陈长清；

【作者基本信息】 华中科技大学 ， 光学工程， 2011， 硕士

【摘要】 Ⅲ族氮化物以其优异的特性得到广泛关注,AlGaN体系材料对应发光波长在210-340nm,适合可应用于白光照明、生化检测、消毒净化等领域的紫外发光器件,成为目前研究的热点。而AlGaN材料,由于体单晶的缺失,一般采用AlN作为生长模板。因此,要得到适用制作器件的高质量AlGaN材料,制备高质量AlN材料成为必须要首先解决的难题。AlN薄膜异质外延,常采用SiC、Si或蓝宝石作为衬底材料。而AlN与这些材料不匹配,晶体质量很差。本文围绕高质量AlN材料的生长展开,采用两步法生长,主要研究缓冲层生长参数对外延层的影响。首先详细阐述MOCVD生长原理,本实验所用的表征设备HR-XRD、AFM等及数据处理方法。根据AlN材料的特性,分析衬底选择、表面预处理、反应腔压力、V/III比等对AlN生长影响,确定相关生长参数。然后探讨缓冲层生长温度对外延层结晶质量和表面形貌的影响。在600℃~870℃区间内选取不同温度生长6个样品,而保持其他生长参数不变。用透射谱、AFM、HR-XRD等检测,发现在690℃~780℃时表面出现原子级台阶,尤其在780℃,晶体质量比较好。温度较低,位错密度大;温度较高,表面粗糙,出现许多小坑。进一步改变缓冲层生长时间,来研究缓冲层厚度的作用。生长3个样品,生长时间为4.4分钟时,样品(0002)面FWHM为116arcsec,(1012)面FWHM为1471arcsec,并且表面出现原子级台阶。而外延层较薄较厚,表面均未出现台阶,晶体质量和表面形貌均很差。根据这两组实验结果,分析缓冲层对外延层的作用机理。最后在前面实验较好的生长模板上,采用连续方式生长一层高温AlN。通过两组实验,在不同生长温度下,改变TMAl和NH3流量、V/III比等来初步探讨连续生长方式对AlN质量的影响。更多还原

【Abstract】 Group-III nitrides attain much attention for their outstanding properties. Due to light-emitting wavelength laying at 210~340nm, AlGaN material suitable for ultraviolet(UV) emitters are used in many applications such as white light illumination, biochemistry survey and sterilizers. Since currently the absence of defect-free bulk substrates has led to AlGaN using an AlN underlying layer to avoid cracks, we need to grow high-quality AlN first. In this thesis, we study the growth of AlN on sapphire and discuss the influence on epitaxial layer of the growth parameter of buffer layer.Firstly, the principle of metal-organic chemical vapor phase deposition(MOCVD) and characterization equipments used in this thesis are stated clearly. Then, we optimize the parameters and proceedings, such as substrate type, pre-process, V/III ratio, pressure of the actor. Six samples were grown on sapphire by MOCVD for different growth temperature of the buffer layer within 600℃~870℃. The high temperature layer was grown with pulsed atomic layer epitaxially(PALE) method. The samples have been examined by high-resolution X-ray diffraction(HR-XRD), atomic force microscopy(AFM), transmission spectrum and so on. Atomic step was observed when the temperature lied in 690℃~780℃, especially at 780℃, at which high crystal quality was obtained.Furthermore, 3 samples have been grown with different growth time of buffer layer. When the time is 4.4 minutes, the X-ray diffraction FWHM were ~116 and ~1471arcsec for the (0002) and (1012 ) planes, and atomic-step was observed. When the growth time was longer or shorter, poor crystal quality and rough surface were found.At last, simultaneous method is studied preliminarily. Based on the better template obtained above, a layer of high temperature AlN was grown with simultaneous method. Two groups of experiment were done with varied TMAl and NH3 flow under 1000℃and 1100℃. Although the samples were crack, we have found high growth temperature and low V/III ratio were benefit for obtaining better crystal quality and smooth surface morphology, which are different from the PALE method. More growth experiments are needed to optimize related parameters and study the mechanism of simultaneous method.更多还原