Structure, optical spectra and biaxial stress of (0002) AlN epilayers grown on c‐sapphire by high‐temperature chemical vapor deposition

Abstract

(0002) AlN epilayers were grown on c‐sapphire at temperatures of 1100, 1200, 1300, 1400, and 1500 °C, respectively, by a homebuilt high‐temperature chemical vapor deposition system. The structure, optical properties and biaxial stress of these epilayers were characterized by scanning electronic microscope, XRD, Raman scattering, and UV absorption. The results revealed that smooth layers were obtained below 1400 °C, while stripe‐shaped and hexagon‐aligned islands grew on the surface of the layer at 1500 °C due to inhomogeneous nucleation in decreased supersaturation. Moreover, the narrowing FWHM of (0002) reflection and phonon modes indicated that the crystal quality improved with increasing temperature. The optical bandgap enlarged with the increasing growth temperature, owing to decreasing dislocations and domain boundaries as well as increasing compressive stress, except that the optical bandgap shrank at 1500 °C because light scattering at the rough surface of the epilayer flattened its optical absorption edge. Furthermore, the results of XRD and Raman studies demonstrated that the biaxial stress in the epilayers turned from tensile stress to compressive stress linearly below 1.8 GPa, resulting in a biaxial stress coefficient of −1.9 cm−1 GPa−1. Therefore, the improving structure together with the increasing biaxial compressive stress of the epilayer enlarged its optical bandgap with a large coefficient of −426 meV GPa−1.

Highly c-axis oriented AlN film grown by unbalanced magnetron reactive sputtering and its electrical properties

“…To control and optimize these properties is an important and active subject for the growth of AlN films. AlN films can be prepared by various techniques such as chemical vapor deposition (CVD) [6,7], reactive magnetron sputtering [1,8], molecular beam epitaxy (MBE) [9,10], ion beam-assisted deposition, and metal organic chemical vapor deposition (MOCVD) [11].…”

Preparation of high-quality thick AlN layer on nanopatterned sapphire substrates with sputter-deposited annealed AlN film by hydride vapor-phase epitaxy

“…The molar concentration of KOH solution was 8 mol l −1 . Specimens for cross-sectional transmission electronic microscopy (TEM) observation along the [11][12][13][14][15][16][17][18][19][20] AlN direction were prepared using a focused ion beam.…”

“…Numerous groups have attempted to grow AlN crystals. [11][12][13][14][15][16] Hydride vapor-phase epitaxy (HVPE) is one of the promising approaches for the preparation of freestanding AlN substrates or thick templates because of its high growth rate and low carbon impurity incorporation. [17][18][19] Several groups have demonstrated the growth of AlN directly on sapphire substrates by HVPE.…”

Epitaxial Growth of AlN on (0001) Sapphire: Assessment of HVPE Process by a Design of Experiments Approach

“…These data allow the determination of mean values of residual stress. For all reactor designs and all optimized conditions by the authors [18][19][20][21][22][23][24][25][26][27][28], FWHM values were in the range of 100 to 600 arcsec and 500 to 800 arcsec for on-axis and off-axis peak, respectively. It is clear that the optimal temperature range is 1200-1400 • C to increase the Al mobility on the surface while avoiding sapphire degradation and/or etching [38].…”

“…In most recent papers [17][18][19][20][21][22][23][24][25][26][27][28] dealing with HVPE growth of AlN at high temperature from chlorinated precursors, intense efforts have been made to reduce defect densities caused by stress [29][30][31] before optimizing optical properties [18]. In situ etching to control void formation and stress release [17], multi-step methods to control island coalescence [32][33][34] or N/Al ratio [33,35], pulse injection of precursors [36], substrate position in turbulent flow [37] have been proposed to reduce strain, high dislocation densities and the appearance of cracks.…”