Characterization of Hazy Morphology on AlInP/GaAs Epitaxial Wafers Grown by Organometallic Vapor Phase Epitaxy

摘要

6-inch AlInP/GaAs epitaxial wafers grown by organometallic vapor phase epitaxy (OMVPE) technique are being developed for light emitting diodes (LEDs) applications. Recently, dislocation configurations in the GaAs substrates and AlInP epilayers have been characterized and conditions for relaxation and formation of misfit dislocations were analyzed. Apart from defects such as dislocations, epilayer surface reveals a hazy morphology formed when the epitaxial growth pressure is increased. It is observed that the epilayer surface is rougher compared to regular clear regions as revealed by both optical microscopy and atomic force microscopy. Additionally, the size of the hazy regions increases with growth pressure but other growth parameters such as growth temperature, V/III ratio, likely influence the onset of hazy morphology. Previous research on the formation of hazy features reports that these can be caused by the deficiency of phosphorus, lowered V/III ratio or stacking faults. However, the hazy features in our case, are different from the ones reported. Synchrotron X-ray topographs of the hazy regions showed blurred contrast, indicating disordered lattice arrangement. Moreover, internal structure of the hazy regions was studied by reciprocal space mapping (RSM), where weakened and broadened peaks around the clear epilayer peak were observed using 004 reflection, indicating continuously varying strain and tilt between the hazy region and the clear region. The thickness of the hazy regions was also analyzed by employing the 002 RSM, where the X-ray penetration depth is lower. Comparison of the 002 and 004 RSMs reveals that at the beginning of epitaxial growth, the epilayers do not suffer from lattice distortion and the formation of the hazy morphology occurs when a critical thickness is exceeded.