Growth of High Quality c-plane AlN on a-plane Sapphire
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1202-I05-02
Growth of high quality c-plane AlN on a-plane sapphire Reina Miyagawa, Jiejun Wu, Hideto Miyake and Kazumasa Hiramatsu Department of Electrical and Electronics Engineering, Mie University, 1577 Kurimamachiya, Tsu 514-8507, Japan [email protected]
Abstract c-plane (0001) AlN layers were grown on (11-20) a-plane and (0001) c-plane substrates by hydride vapor phase epitaxy (HVPE) and metal-organic vapor phase epitaxy (MOVPE). The growth temperature was adjusted from 1430 to 1500 0C and the reactor pressure was kept constant at 30 Torr. Mirror and flat c-plane AlN were obtained on both a-plane and c-plane sapphire. The crystalline quality and surface roughness, evaluated by high-resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM), respectively, improved with increasing growth temperature. The full width at half maximum (FWHM) values of (10-12) diffraction were 519 and 1219 arcsec for c-plane AlN grown on a-plane sapphire and c-plane sapphire, respectively. This indicates that the a-plane sapphire substrate has the advantage of providing decreased dislocation density.
Introduction The strong demand for high-efficiency deep-ultra violet light-emitting diodes (UV-LEDs) and sensors has led to renewed interest in the growth of high-quality AlN. However, the growth of high-quality, thick, and crack-free AlN is very difficult owing to the low surface migration of Al atoms, the large lattice and thermal mismatches in the absence of native substrates, the strong parasitic reaction at elevated temperatures, and the narrow growth window. Some methods, such as maskless lateral epitaxy overgrowth (LEO) [1], and similar techniques such as the use of a patterned AlN template [2] or a patterned substrate [3], pulsed atomic layer epitaxy (PALE) and similar methods [4, 5], and a V/III ratio modulation multi-interlayer method [6], have proven to be effective at decreasing the threading dislocation (TD) density, particularly that of edge-type dislocations, and improving the crystalline quality. Chen et al. used a combination of PALE and a modulation growth (3D-2D) method to reduce the FWHM value of (10-12) diffraction on a SiC substrate to 363 arcsec [4]. However, LEO requires ex situ pattern fabrication and PALE places a critical demand on the shutters of equipment. These methods are also complicated from a technological viewpoint, and a simple method for growing high-quality AlN is desirable. Although c-plane sapphire is normally used as a substrate, a-plane sapphire is actually preferable for some applications such as edge-emitting lasers [7] owing to the easy cleavage along the r-plane. Despite the fact that improved GaN has been grown on a-plane sapphire [8], the growth of AlN on a-plane sapphire by MOVPE or HVPE has seldom been reported. In this study, we report on a simple method of AlN growth on a-plane and c-plane sapphire substrates by HVPE and MOVPE without the use of LEO, PALE, or a multi-interlayer.
Experimental procedure A c-plane AlN layer was grown on c-plane and a-plane sa
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