Growth of High-Quality GaN Heterostructures Based on AlN Template +

AlN templates are available for GaN heterostructure growth. Please contact at [email protected] for additional wafer information.

Gallium nitride (GaN)-based heterostructures serve as the core material system for high-performance optoelectronic and power electronic devices. However, the quality of heterostructures is limited by factors such as interfacial defects, lattice mismatch, and polarization effects. Aluminum nitride (AlN) thin films, due to their lattice constant and thermal expansion coefficient being close to those of GaN, have become a key buffer layer for improving heterostructure quality. Studies show that using sapphire based AlN templates not only regulates the polarity growth of GaN but also reduces dislocation density through complementary deformation mechanisms, laying the foundation for high-quality heterostructure epitaxy.

1. The Key Role of AlN Template in GaN Epitaxy

Single crystal AlN templatess significantly improve GaN epitaxial quality through unique deformation mechanisms. Sumiya et al. (2020) found that during the initial growth stage of GaN, the a-lattice constant of the AlN template gradually increased, and the full width at half maximum (FWHM) of the XRD rocking curve expanded from 50arcsec to 300arcsec before recovering, indicating dynamic lattice adjustment in AlN. This complementary deformation allows the AlN film to function similarly to a low-temperature buffer layer, enabling GaN to achieve a smooth surface and excellent crystalline quality in a shorter time (10 min) and at a lower temperature (930 °C). Photothermal deflection spectroscopy further confirmed that GaN grown on AlN templates exhibits lower Urbach energy (30meV) and fewer band-gap defect states.

Fig. 1 Evolution of structural parameters of the AlN template with GaN growth time: (a) XRD ω-2θ scans of the AlN (0002) plane; (b) variation in diffraction peak area of the AlN (0002) and (10-14) planes with GaN deposition time; (c) variation curves of a- and c-lattice constants of AlN with GaN growth time

Fig. 2 Evolution of crystal quality of the AlN template and GaN thin film with growth time: (a) FWHM of XRD rocking curves for the AlN (0002) and (10-14) planes as a function of GaN deposition time; (b) corresponding FWHM variation of rocking curves for GaN thin film directly grown on AlN

Fig. 3 Comparison of photothermal deflection spectra of GaN thin films grown on different substrates: sapphire substrate (blue) and AlN template (red)

2. Control of GaN Polarity and Interfacial Defects by AlN Thickness

Li et al. (2021) systematically investigated the fine-tuning effect of AlN thickness on GaN growth behavior. When the AlN thickness was 150 nm, a smooth N-polar GaN surface free of hexagonal defects was obtained, with a spiral dislocation density as low as 4.2 × 10⁸ cm⁻². Reducing the thickness to 80nm resulted in numerous columnar inversion domains and deteriorated crystal quality. Increasing the thickness to 200 nm caused GaN polarity to reverse to Ga-polarity, with TEM revealing the formation of abundant pyramid-like defects at the interface. This indicates that AlN thickness, by regulating interfacial defect structures and strain distribution, serves as an important tool for polarity engineering.

Fig. 4 Optical micrographs of GaN thin film surfaces grown with different AlN buffer layer thicknesses: (a) image of sample S1 (AlN: 70nm) at 50× magnification; (b) enlarged view of sample S1 at 200× magnification; (c) image of sample S2 (AlN: 150nm); (d) image of sample S3 (AlN: 200nm)

Fig. 5 X‑ray diffraction analysis of GaN thin films: (a) ω-2θ scan curves of the (000-2)/(0002) planes for samples S1–S3; (b) corresponding XRD rocking curves and FWHM values for the (000-2)/(0002) planes; (c) Williamson–Hall plots; (d) variation of FWHM with tilt angle.

Fig. 6 AFM images of GaN thin film surfaces: (a) sample S1 (AlN: 70nm) showing step bunching, RMS roughness 5.73nm; (b) sample S2 (AlN: 150nm) with a smooth surface, RMS roughness 0.85nm; (c) sample S3 (AlN: 200nm) exhibiting step-flow growth mode, RMS roughness 1.24nm.

Fig. 7 Cross-sectional TEM images and selected area electron diffraction patterns of different samples: (a–c) TEM, HRTEM, and SAED patterns of sample S1 (AlN: 70nm), showing columnar inversion domains; (d–g) TEM, clear HRTEM of the AlN/GaN interface, AlN/sapphire interface, and SAED patterns of sample S2 (AlN: 150nm), revealing moderate interfacial fluctuations; (h–j) TEM, HRTEM near pyramid-like defects, and SAED patterns of sample S3 (AlN: 200nm), with severe interfacial undulations and numerous pyramid defects.

3. Construction of High-Quality Heterostructures Based on AlN Templates

Building on optimized GaN/AlN thin films, Sumiya et al. (2020) successfully grew high-quality InGaN thin films and AlGaN/InGaN heterostructures. By adjusting the InGaN thickness to 90nm, the minimum Urbach energy was achieved, indicating the lowest structural disorder at this thickness. The fabricated Al0.25Ga0.75N/In0.055Ga0.945N heterostructure exhibited clear Shubnikov–de Haas oscillations at 1.7K, with a two-dimensional electron gas mobility of 2000 cm²·V⁻¹·s⁻¹ and a carrier density of 7.2 × 10¹² cm⁻². This demonstrates that heterostructures based on AlN templates possess excellent interfacial quality and transport properties.

Fig. 8 Photothermal deflection spectroscopy and structural disorder analysis of InGaN thin films grown on AlN templates

Fig. 9 Magnetoresistance and Shubnikov–de Haas oscillation curves of the AlGaN/InGaN heterostructure

AlN templates, through their unique lattice adjustment capability, polarity control function, and defect suppression mechanisms, provide an effective platform for the epitaxial growth of high-quality GaN heterostructures. An appropriately thick AlN layer enables the synergistic optimization of crystal quality and polarity growth, while characteristics such as SdH oscillations in heterostructures demonstrate their potential for application in high-efficiency electronic devices.

Whether you need AlN templates for research or for industrial applications, please contact us email at [email protected] and [email protected].

 

References:

1. Sumiya, M., Fukuda, K., Yasiro, S., & Honda, T. (2020). Influence of thin MOCVD-grown GaN layer on underlying AlN template. Journal of Crystal Growth, 532, 125376.
2. Sumiya, M., Kindole, D., Fukuda, K., Yashiro, S., Takehana, K., Honda, T., & Imanaka, Y. (2020). Growth of AlGaN/InGaN/GaN heterostructure on AlN template/sapphire. physica status solidi (b), 257(4), 1900524.
3. Li, Y., Hu, X., Song, Y., Su, Z., Wang, W., Jia, H., … & Chen, H. (2021). The role of AlN thickness in MOCVD growth of N-polar GaN. Journal of Alloys and Compounds, 884, 161134.