Comprehensive characterization of low-damaged GaN surface exposed to NH3 plasma toward plasma-induced metalorganic chemical vapor deposition

Abstract

To examine the application of plasma-induced metalorganic chemical vapor deposition (MOCVD) toward the epitaxial growth of III-V nitride semiconductors, a GaN surface exposed to NH3 plasma at 0.4 kPa from a novel plasma source was comprehensively characterized using physical and chemical techniques. The exposure time (10–40 min) dependence at 700 °C and substrate temperature (200–700 °C) dependence for 20-min exposure were investigated using various methods, such as photoluminescence (PL), vacuum ultra-violet (VUV) spectroscopic ellipsometry, transmission electron microscopy (TEM), atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and current–voltage (I–V) characteristics. The PL intensity decreased linearly with the increase in exposure time and was maintained at ∼ 60% intensity after an exposure of 10 min. Compared to that of the as-grown GaN, the dielectric function (DF) of the exposed GaN was slightly modulated. For temperature dependence, the PL intensity decreased linearly with temperature and remained at ∼ 80% intensity at 700 °C. The I–V characteristics showed ∼ 50% decrease in conductivity for an exposure time of 20 min at 700 °C. TEM and XPS revealed extremely low modifications. In case of long-term exposure, hexagonal pits and particle-like nanostructures appeared at the surface. Based on the TEM results, the pit is attributed to threading dislocations, and the nanostructure is not really a particle but a protrusion with a GaN crystal structure. From this study, it can be concluded that, compared to the XPS and TEM techniques, optical techniques such as PL measurement and VUV-SE have higher sensitivity for detecting the effect of NH3 plasma exposure on the GaN surface. The comprehensive characterizations revealed that no significant damage is induced by the plasma exposure in the time corresponding to the usual growth time of an InGaN quantum well, that is, several minutes.