Fundamental Study of Nitride Semiconductor Materials for UV-Wavelength Laser Diode

在蓝宝石和碳化硅衬底上展示了许多基于InGaN的光电子和电子器件的应用。然而，由于GaN和AlGaN材料具有光子能量高、激光光斑尺寸小等优点，利用GaN和AlGaN材料制作的紫外光器件尚未问世。获得高质量的GaN和AlGaN异质外延是实现紫外光器件的必要条件。GaN和AlN在蓝宝石尤其是硅衬底上的异质外延生长过程尚不清楚。因此，本文研究了在蓝宝石和硅衬底上分子束外延生长GaN和在Si衬底上MEE生长GaN的机理。首先，本文研究了在蓝宝石衬底上采用室温沉积的a-GaN缓冲层生长高质量GaN层的方法。结果表明，采用非晶GaN缓冲层在蓝宝石(0001)衬底上成功地生长出了表面平坦的GaN外延层，然后利用AlN缓冲层在6H-SiC衬底上成功地生长了GaN缓冲层。发现在AlN缓冲层和GaN外延层之间的异质界面处产生了几乎丝状的位错。最后，我们尝试用分子束外延技术在Si(111)衬底上生长GaN缓冲层。用MEM方法在Si(111)衬底上有效地生长出了薄的AlM层，AFM观察发现，在AlN/Si(111)衬底上生长的60 nm厚的GaN外延层表面非常平坦，这一结果可用于在Si衬底上制备高质量的GaN外延层和蓝波光电子器件材料。

Many InGaN-based applications of optoelectronic and electronic devices are demonstrated on sapphire and SiC substrates. UV-wavelength devices with GaN and AlGaN materials, however, have not yet been performed regardless of many advantages such as the high photon energy and a small spot size of laser beam. It is necessary for realization of UV-wavelength devices to obtain high quality GaN and AlGaN hetero epilayrs. Heteroepitaxial growth processes of GaN and AlN on sapphire and especially Si substrates are not clear. Therefore, it has been investigated the growth mechanism of GaN by MBE and AIN by MEE on sapphire and Si substrates.At first, It has been studied that the high quality GaN layr was grown on sapphire substrate using a-GaN buffer layr deposited at room temperature. It has been found that the amorphous GaN buffer laver deposited at room temperature changes to the single crystal by annealing at 700ﾟC.It is concluded that the GaN epilayr with the flat surface is successfully grown on sapphire (0001) by using the amorphous GaN buffer layr.Then a GaN layr was successfully grown on 6H-SiC substrate using the AlN buffer layr. It was found that the almost threading dislocations are generated at the hetero interface between the AlN buffer layr and the GaN epilayr.Finally, we attempted to grow a GaN layr on Si (111) substrate by MBE using an AlN buffer layr by MEE method. The thin AlM layr was effectively grown on the Si (111) substrate by MEE.It is also found that the surface morphology of the 60nm-thick GaN epilayr on the AlN/Si (111) substrate was extremely flat by AFM observation.These results can be applied tothe fabrication of the high quality GaN epilayr on the Si substrate and the materials for the blue-wave length optoelectronic devices.