Analysis of Surface Morphology Control Mechanism of AlN on Sapphire +

AlN on sapphire templates are available for deep ultraviolet optoelectronic devices, acoustic resonators, and power electronic devices. For product details, please contact: [email protected]. The surface morphology directly affects the performance and reliability of the device. Based on three related studies, this article systematically summarizes the main factors affecting the surface morphology of AlN thin films, including growth temperature, reaction chamber pressure, V/III ratio, and the relationship between surface roughness and oxygen impurity concentration.

1. Influence of Growth Temperature on Surface Morphology

The growth temperature is a key parameter that affects the quality and surface roughness of AlN crystals. Lin et al. found that increasing the growth temperature during MOCVD growth significantly enhances the surface migration ability of Al atoms, promotes two-dimensional layered growth, and thus reduces surface roughness. The AlN thin film grown at 1300°C exhibits excellent crystal flatness with a full width at half maximum (FWHM) of 0.033° and a surface roughness of only 8.4nm for the (002) crystal orientation X-ray rocking curve.

Fig. 1 X-ray rocking curve of AlN film (002) peak: (a) grown at different growth temperatures and fixed reactor pressures (5500Pa); (b) Growing under different reactor pressures at a fixed growth temperature (1300℃). X-ray rocking curve of AlN thin film (102) peak: (c) grown at different growth temperatures under a fixed reactor pressure (5500Pa); (d) Growing under different reactor pressures at a fixed growth temperature (1300℃)

Fig. 2 Variations of Roughness with growth temperature and reactor pressure

2. Regulation of Reaction Chamber Pressure and V/III Ratio

The pressure in the reaction chamber directly affects the growth rate and the degree of parasitic reactions in the gas phase. Lin et al. pointed out that low-pressure conditions (such as 50mbar) can help suppress pre reactions in the gas phase, reduce the formation of AlN particles, and thus improve surface morphology. Streicher et al. found that high V/III ratios (such as 2560) can promote atomic step flow growth mode, achieve slow layer by layer growth, effectively cover three-dimensional nucleation layers, and reduce dislocation density and surface roughness. However, excessive pressure (such as 95mbar) can lead to step-bunching, indicating insufficient surface supersaturation, which is not conducive to smooth growth.

Fig. 3 AFM under growth pressures ranging from 50mbar to 95mbar (2μm²): (a) 50mbar; （b）80mbar; (c) 90mbar; (d) As the pressure increases, the full width at half maximum of reflections 00.2 and 10.2 decreases; (e) Growth rate decreases with increasing pressure

3. Relationship Between Surface Roughness and Oxygen Impurity Concentration

Surface roughness not only affects the optical and electrical properties of thin films, but is also closely related to impurity doping. Zhang et al. found through cathodoluminescence (CL) and secondary ion mass spectrometry (SIMS) analysis that the concentration of oxygen impurities in AlN is positively correlated with the surface roughness during growth. The rough surface exposes more m-faces or a-sides, which have stronger adsorption capacity for oxygen, resulting in uneven distribution of oxygen impurities, which in turn leads to specific changes in the luminescence intensity of oxygen impurities with temperature variation. At low temperatures, the luminescence intensity is enhanced due to the capture of charge carriers by oxygen impurities; At high temperatures, the luminescence intensity decreases due to the thermal excitation of charge carriers. A smooth c-face can effectively suppress oxygen doping and improve material purity.

Fig. 4 Growth conditions of AlN samples

Fig. 5 (a) the integrated intensity of oxygen impurity related luminescence peaks varies with temperature; (b) SIMS of oxygen distribution in AlN samples

In summary, the surface morphology of AlN thin films is influenced by multiple process parameters. High temperature, low pressure, and high V/III ratio are beneficial for achieving a smooth and low defect surface morphology, while controlling surface roughness further affects impurity distribution and device performance.

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

 

References:

1. Lin, B., Cai, Y., Wang, Y., Zou, Y., Gao, C., Liu, Y., … & Sun, C. (2023). Effects of growth temperature and reactor pressure on AlN thin film grown by metal-organic chemical vapor deposition. Thin Solid Films, 783, 140037.
2. Streicher, I., Leone, S., Kirste, L., & Ambacher, O. (2022). Effect of V/III ratio and growth pressure on surface and crystal quality of AlN grown on sapphire by metal-organic chemical vapor deposition. Journal of Vacuum Science & Technology A, 40(3).
3. Zhang, Y., Yang, J., Liang, F., Liu, Z., Hou, Y., Liu, B., … & Zhao, D. (2024). Dependence of oxygen impurity concentration in AlN on the surface roughness during growth. Journal of Applied Physics, 135(16).