The Study Of The Growth Of High-quality AlN On Sapphire

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.