In‐situ deposited SiN_x nanomask for crystal quality improvement in AlGaN

Abstract

We report the growth of high crystal quality Al0.3Ga0.7N directly on sapphire substrates with metalorganic vapour phase epitaxy. We studied the improvements in crystal quality by introducing an in‐situ deposited SiNx interlayer. It acts as a nanomask which results in termination of the dislocations near the interface between the nanomask and epilayer. The epilayers with no SiNx interlayer have very low density of screw type dislocations evident from transmission electron microscopy (TEM) investigations confirmed by a very narrow X‐ray diffraction symmetric reflection (60”). This is a result of our oxygen doped AlN nucleation layer used to grow such epilayers. On the other hand, such epilayers have very broad XRD asymmetric reflections (typically a few thousand arcsec) indicating a high density of edge type dislocations. We could decrease the latter which are the main existing dislocations in our AlGaN epilayers. In TEM micrographs, we observed the formation of dislocation “bundles” when introducing SiNx interlayers. This phenomenon promotes the dislocation free areas on the surface of the wafer. We carried out accurate optimizations of the SiNx deposition. Consequently, we could grow high quality Al0.3Ga0.7N epilayers with much narrower XRD asymmetric peaks–782” with total sample thickness of 1.4 µm (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

TEM investigations on growth interrupted samples for the correlation of the dislocation propagation and growth mode variations in AlGaN deposited on SiN interlayers

“…ABABABCBCBCBC. Such intrinsic I 1 type stacking fault has to be bounded by a FrankShockley partial dislocation with Burgers vector b¼1/6 [20][21][22][23]. It is known, that the I 1 type BSF is likely to be formed during the growth process and not due to distortions induced by stress during or after growth [33].…”

“…For all samples the growth was started by a low temperature 20-nm-thick oxygen doped AlN:O nucleation layer to improve the crystal quality [19], followed by a 150-nm-thick high temperature Al 0.2 Ga 0.8 N layer. Subsequently an intermediate nominal SiN x sub-monolayer was in-situ deposited on the Al 0.2 Ga 0.8 N, using silane (SiH 4 ) as precursor with a deposition time of 4 min at a pressure of 160 hPa and at the same temperature as for AlGaN growth [20,21]. The growth of sample S1 was completed by a 1-mm-thick Al 0.2 Ga 0.8 N layer, whereas the growth of the same layer was stopped after 4 and 13 min for sample S2 and S3, respectively.…”

Correlation of structural and optical properties of AlGaN films grown on SiN-treated sapphire by MOVPE

“…However, several methods have been suggested to reduce the effects associated with mismatches between the AlGaN layer and sapphire substrate, e.g., the deposition of a low-temperature buffer layer of GaN or AlN on the substrate [24] and the epitaxial lateral overgrowth [6]. Furthermore, the use of an in situ SiN x nano-masking on the sapphire substrate, the so-called Si/ N treatment, has been proved to be a promising technique to enhance the AlGaN layer quality [25]. An improvement in the AlGaN crystalline quality has also been reported when a high-temperature GaN layer, i.e., GaN template, is sandwiched between the AlGaN layer and the substrate [26].…”

Effects of the diameter of thermally generated nanopits on carrier dynamics in AlGaN/GaN heterostructures

“…4,24 Hence, reducing point defects in AlGaN layers is the key to improving the performance of AlGaN-based devices. For this purpose, various strategies and growth techniques have been suggested, such as the epitaxial lateral overgrowth, 15 the SiN treatment of sapphire substrate, 25 the deposition of low-temperature GaN or AlN buffer layer, 26 and the insertion of high-temperature GaN template layer between the buffer layer and the AlGaN active layer. 4 Despite the noticeable improvement in the layer quality using the aforementioned methods, the density of point defects in AlGaN is still higher than the level aimed to reach the full potential of AlGaN-based applications and devices.…”