MS-8-P-5731 TEM investigation of semipolar GaN grown on Si(001) offcut substrates using AlN and 3C-SiC buffer layer

Gallium nitride (GaN) has been recognized as a promising material for high-performance light-emitting devices. Commercial nitride semiconductors are grown on single-crystal substrates with (0001) oriented surfaces. However, electrostatic fields generated by the spontaneous and piezoelectric polarization along [0001] axis in wurzite GaN layers lower the luminous efficiency of the devices. One way to increase the efficiency is use of GaN layers grown on semipolar planes [1]. Mostly, GaN-based devices are fabricated using silicon carbide or sapphire substrates. These substrates are expensive and insulating and are not available in large diameter. On the other hand, silicon is inexpensive material and has reasonable thermal and electrical conductivity. Si(001) substrate is preferable for GaN growth since Si(001) single crystal is the material of the electronic silicon industry.
In this work results of TEM investigation of thick (up to 15 µm) semipolar GaN layers grown on 1.5-inch Si(001) offcut substrates with 3C-SiC and AlN buffer layers are presented. The offcut angles were 0°, 4° and 7° toward the Si [110] direction (samples 1, 2 and 3). The growth of GaN layer was realized by hydride-chloride vapor-phase epitaxy (HVPE) on AlN/3C–SiC/Si template. The SiC and AlN buffer layers were formed by solid-phase epitaxy [2] and HVPE respectively without any prior masking and etching of silicon substrate.
It has been established that GaN layer of sample 1 consists of oriented wurzite grains. The [2-1-10] axis of all GaN grains is parallel to [110] directions of silicon substrate. The [0001] axis of the majority of GaN grains is near parallel to <111> Si so the angle between GaN [0001] axis and normal to substrate is equal approximately 52°. Grains contain basal plane stacking faults with a density varying from grain to grain within 2×10⁵ - 3×10⁶ cm^-1.
In the case of samples 2 and 3 structure of the GaN layer changed significantly. The layer is a single crystal and the density of stacking faults decreased considerably (fig. 1). Unusual orientation relations were revealed in these heterostructures: the GaN [0001] axis is still near parallel to Si<111>, however, the angle between AlN[0001] and GaN[0001] is ~1.5° (fig. 2).

References
1. A. E. Romanov _ T. J. Baker, S. Nakamura, J. S. Speckb. Strain-induced polarization in wurtzite III-nitride semipolar layers// J. Appl. Phys. 100, 2006, p. 023522(1-10)
2. Kukushkin S.A., Osipov A.V. A new method for the synthesis of epitaxial layers of silicon carbide on silicon owing to formation of dilatation dipoles // J. Appl. Phys., 113, 2013, P. 024909(1-7)