Raman spectroscopy of macroscopic defects of GaAs grown by molecular beam epitaxy

Macroscopic defects of the GaAs surface grown by molecular beam epitaxy (MBE) have been investigated by using a micro-probing method of Raman spectroscopy. Especially, the oval defects, the most common macroscopic defects in MBE GaAs, were focused in this study. In Raman spectroscopy for the oval defect on the (100)GaAs surface, TO phonon mode of the 269 cm^-1 peak was observed. This indicates that the oval defects can include the (111) growth direction or the amorphized surface. The TO/LO intensity ratios for the defects are in the range from 0.3 to 1.0. In the sample grown under the condition that the substrate temperature is 580° C with the As/Ga ratio of 20, the density of the oval defects is about 200 cm^-2 at a growth thickness of 5 μm. With increasing thickness of the epilayer, the density and the size of the α-tye oval defect increased, while the TO/LO ratio decreased. From the spatial measurement by Raman spectroscopy for the α-type oval defect, it is supposed that the α-type oval defect remains in a rather good crystalline state and its orientation along the (100) growth direction is much closer to the (111) direction, but the growth direction of the defect might tend toward the (100) direction with a thicker layer.