High Temperature Characteristics of AlN on Sapphire: Electrical, Stress, and Optical Behavior +
PAM-XIAMEN can supply sapphire based aluminum nitride(AlN) films. For product details, please consult: [email protected].
Wide bandgap semiconductor AlN has shown significant potential in high-temperature applications due to its excellent properties. However, the performance of AlN devices in high-temperature environments is significantly affected by the temperature dependence of their material properties, specifically involving changes in electrical transport behavior, residual stress states, and optical behavior. Therefore, the systematic study of the electrical, stress, and optical properties of AlN at different temperatures has important theoretical guidance significance for promoting its practical application under high temperature conditions.
1. Temperature Dependence of Electrical Properties of Si Injected AlN Layer
Okumura et al. investigated the electrical properties of Si ion implanted sapphire based AlN layers in the temperature range of 300-1173K. Research has shown that as the temperature increases, the thin layer resistance (Rs) of Si injected AlN gradually decreases from its high value at 500K, and drops to 1.0×10 ⁵ Ω/□ at 1100K, mainly due to a significant increase in carrier concentration (ne) (from 2.5×10 ¹⁶cm⁻³ at 500K to 1.9×10¹⁸ cm⁻³ at 900K). The electron mobility (μe) decreased from 19cm²/V·s to 3cm²/V·s due to enhanced phonon scattering. In addition, the specific contact resistivity (ρc) decreased to 4.0×10⁻³Ω·cm² at 1100K, indicating that the thermal emission mechanism dominates the current transport at high temperatures.
Fig. 1 (a) Temperature dependence of thin layer resistance and specific contact resistivity of Si injected AlN layer; (b) Temperature dependence of electron mobility and electron concentration in Si injected AlN layer
At the device level, AlN Schottky barrier diodes (SBDs) still exhibit good rectification characteristics up to 1100K, with a breakdown voltage of 610V and a barrier height of 3.5eV. Metal semiconductor field-effect transistors (MESFETs) can achieve gate control at 1000K, with a maximum transconductance of 2.8 × 10⁻³S/mm, indicating that AlN devices have the potential for stable operation at extreme temperatures.
Fig. 2 AlN SBD: (a) J-V characteristics; (b) Temperature dependence of ideal factor and apparent barrier height
Fig. 3 AlN MESFET: (a)Transmission characteristics; (b) Temperature dependence of maximum transconductance and threshold voltage
2. Stress Temperature Dependence and Control of AlN Thin Films
Wei et al. analyzed the stress evolution of AlN in the temperature range of 80-300K using Raman spectroscopy and XRD. Research has found that as the temperature increases, biaxial stress gradually relaxes: AlN thin films grown on conventional sapphire substrates (CSS) experience a decrease in stress from 1.59GPa to 0.60GPa; The stress of the sample grown on the nano patterned sapphire substrate (NPSS) decreased from 0.90GPa to 0.38GPa. The reason for the lower stress of NPSS samples is that the nanopore structure provides a release channel for stress, effectively alleviating strain accumulation caused by lattice mismatch (≈ 13.2%) and differences in thermal expansion coefficients (≈ 45.4%).
Fig. 4 Relationship between biaxial stress and temperature in AlN thin film
High temperature annealing (1550°C) further promoted defect healing and stress release, reducing the strain value from 0.1606% to 0.1164%. At the same time, the full width at half maximum (FWHM) of the X-ray rocking curve decreased, indicating an improvement in crystal quality. Transmission electron microscopy (TEM) analysis shows that the stress state gradually transitions from tensile stress at the interface to compressive stress on the surface, and the “keyhole” structure in the NPSS sample facilitates uniform release of internal stress.
Fig. 5 (a) XRD of AlN thin film; (b) Rocking curve
Fig. 6 TEM image of cross-section of AlN sample A on CSS
Fig. 7 TEM image of cross-section of AlN sample B on NPSS
3. Temperature Dependent Optical Properties of AlN
Wei et al. found that the refractive index (n) and extinction coefficient (k) of AlN undergo a red shift with increasing temperature through temperature dependent ellipsoidal polarization spectroscopy (SE) and ultraviolet visible spectroscopy (UV Vis) analysis. In the range of 300-850K, the bandgap energy (Eg) decreased from 6.16eV to 5.73eV for CSS samples and from 6.06eV to 5.64eV for NPSS samples, in accordance with Varshni’s empirical formula. This change is mainly due to the band contraction caused by lattice thermal expansion and electron phonon interactions.
Fig. 8 Temperature dependence of AlN/Sapphire optical properties
AlN materials exhibit excellent electrical stability, controllable stress states, and predictable optical behavior in high-temperature environments. Si injected AlN devices can still operate at 1100K, and the NPSS substrate and high-temperature annealing process effectively reduce residual stress and defect density, improving material quality. The redshift behavior of optical bandgap with temperature conforms to the laws of semiconductor physics, providing a basis for its application in high-temperature optoelectronic devices.
Whether you need AlN on Sapphire template for research or for industrial applications, please contact us email at [email protected] and [email protected].
References:
- Okumura, H., Watanabe, Y., & Shibata, T. (2023). Temperature dependence of electrical characteristics of Si-implanted AlN layers on sapphire substrates. Applied Physics Express, 16(6), 064005.
- Wei, W., Peng, Y., Wang, J., Farooq Saleem, M., Wang, W., Li, L., … & Sun, W. (2021). Temperature dependence of stress and optical properties in AlN films grown by MOCVD. Nanomaterials, 11(3), 698.