Plastic Relaxation of Stressed Semipolar AlN( $$10\bar {1}1$$ ) Layer Synthesized on a Nanopatterned Si(100) Substrate
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ICAL SCIENCE OF MATERIALS
Plastic Relaxation of Stressed Semipolar AlN(1011) Layer Synthesized on a Nanopatterned Si(100) Substrate V. N. Bessolova,*, E. V. Konenkovaa, and V. N. Panteleeva aIoffe
Institute, St. Petersburg, 194021 Russia *e-mail: [email protected]
Received March 25, 2020; revised June 15, 2020; accepted June 30, 2020
Abstract—Plastic relaxation of a stressed semipolar AlN(10 11) layer synthesized on a nanopatterned Si(100) substrate has been investigated using scanning electron microscopy. It is shown that the application of a nanorelief consisting of triangular nanogrooves with inclined faces close to the Si(111) plane in a semipolar AlN layer can lead to the formation of cracks only in the direction perpendicular to a groove. Model concepts of plastic relaxation of the stressed semipolar layer are based on comparison of the threshold stress, above which cracks appear, with the thermomechanical stresses emerging because of the difference between the thermal expansion coefficients of the AlN/Si structure. DOI: 10.1134/S1063784220120051
In the last few years, considerable attention has been paid to III nitrides used for preparing effective optoelectronic devices [1]. However, gallium and aluminum nitrides are piezoelectric materials, and the use of the (0001) plane in optoelectronic devices leads to a manifestation of the Stark effect; for this reason, the replacement of the polar layer in these devices by semipolar or nonpolar layers becomes attractive [2]. At present, Si(100) is considered as a promising substrate for synthesis of GaN layers because of its low cost, large sizes, and quite high thermal conductivity, in addition to as a substrate with a potential for integration of gallium nitride and silicon-based optoelectronics. Attempts are being made at present to synthesize semipolar gallium and aluminum nitrides on silicon substrates [3], as well as on 3C–SiC/Si templates [4, 5]. However, because of a large mismatch between AlN and Si lattices, epitaxial AlN layers grown on Si substrates must withstand a considerable tensile stress, which may lead to cracking upon cooling from the epitaxy temperature to room temperature due to the difference in the thermal expansion coefficients of AlN and Si [6]. Cracking of polar GaN layers during the epitaxy on a sapphire substrate was considered in [7]. In the epitaxy of polar GaN on a silicon, attempts were made at avoiding cracking by using a microstructured Si(100) substrate [8]. However, to our knowledge, the peculiarities of cracking during the formation of AlN semipolar layers have not been described in the literature. This communication is aimed at clarifying the conditions for the emergence of plastic relaxation of the
stressed semipolar AlN layer on a nanostructured NP–Si(100) (nanopatterned Si(100)) substrate. For this purpose, the V-structured substrate with average period λ ≈ 80 nm and height h ≈ 65 nm was formed using the Wostec technology [9] on the Si(100) substrate with a surface orientation to within ±0.5° (Fig. 1a). At the top
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