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

在蓝宝石和SiC衬底上展示了许多基于InGaN的光电和电子器件的应用。然而，具有GaN和AlGaN材料的UV波长器件尚未被执行，而不管许多优点，例如高光子能量和激光束的小光斑尺寸。获得高质量的GaN和AlGaN异质外延层是实现紫外波长器件的必要条件。GaN和AlN在蓝宝石，特别是Si衬底上的异质外延生长过程尚不清楚。本文首先研究了在蓝宝石和Si衬底上MBE生长GaN和外延生长AlN的生长机理，并利用室温下淀积的a-GaN缓冲层在蓝宝石衬底上生长了高质量的GaN层。发现室温下沉积的非晶GaN缓冲层经700 ℃退火后转变为单晶，从而得出利用非晶GaN缓冲层在蓝宝石（0001）衬底上成功生长出表面平整的GaN外延层，并利用AlN缓冲层在6 H-SiC衬底上成功生长出GaN层的结论。最后，我们尝试了在Si（111）衬底上以AlN缓冲层为衬底，用MBE方法生长GaN层。用AFM观察发现，在AlN/Si（111）衬底上生长的60 nm厚的GaN外延层表面非常平整，这些结果可用于在Si衬底上制备高质量的GaN外延层和蓝波段光电子器件材料。

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.