Growth of GaN thin film on the sapphire covered by hexagonal non-closed packed hollow silica particles

Abstract

In few decades, III-V compound semiconductors have attracted much attention due to theirs excellent optical properties. Especially, because of the suitable band gap of GaN, it is selected and used in the light emitting diode (LED) devices. Comparing with conventional lighting devices, LED devices have many advantages, such as high lighting efficiency, long lifetime of devices, and less heating lighting effect. However, the performance of conventional GaN based LED devices is suffered by high threading dislocation density, low external extraction efficiency and wafer bowing effect. In order to overcome these problems, a method of growth of GaN thin film on the sapphire covered by hexagonal non-closed packed (HNCP) hollow silica particles was proposed in this study. This method concluded three steps. At first, various sized monodisperse shrinkable PS-silica core-shell beads were synthesized. As-synthesized particles had two important features, one was the shrinkable shell, and another was decomposable core. Second step was patterning. Sapphire substrate coated by monolayer core-shell particles with hexagonal closed packed (HCP) structure was fabricated by spin-coating method. Then after thermal treatment, HCP core-shell particles array was transformed to HNCP hollow silica particles array. The main defects in HNCP silica hollow particle pattern was the connection between particles. Due to connection between neighboring particles, HNCP pattern was not perfect. These connection defects were inevitably formed during thermal treatment with low ramping time. However in the case of thermal treatment with high ramping time, connection between neighboring particles could be avoided. In the end, GaN thin film was grown on patterned substrate by metal organic chemical vapor deposition (MOCVD). Due to high coverage percentage of hollow silica beads mask, existence of bilayer and aggregate particles, and imperfect growth condition, GaN films was not fully coalescent. SEM images show that self-assembly HNCP hollow silica particle pattern was successfully embedded with GaN thin films with ultra-high coverage percentage of hollow silica beads. By using HNCP hollow silica beads coated substrate, XRD FWHM value of (102) plane was reduced from 521.1 to 335.1 arcsec, PL intensity was increased by a factor of 7, the PL peak was shift from 361.8 to 363.5. We concluded that GaN films are grown with higher crystal quality, higher external quantum efficiency and lower stress by inserting HNCP hollow silica beads.