Abstract
The effect of high-temperature annealing (HTA) at 1700 °C on AlN films grown on 4H–SiC substrates by metalorganic vapor phase epitaxy has been studied. It is shown that the structural quality of the AlN layers improves significantly after HTA similar to what has been demonstrated for AlN grown on sapphire. Dislocation densities reduce by one order of magnitude resulting in 8 × 108 cm−2 for a-type and 1 × 108 cm−2 for c-type dislocations. The high-temperature treatment removes pits from the surface by dissolving nanotubes and dislocations in the material. XRD measurements prove that the residual strain in AlN/4H–SiC is further relaxed after annealing. AlN films grown at higher temperature resulting in a lower as-grown defect density show only a marginal reduction in dislocation density after annealing. Secondary ion mass spectrometry investigation of impurity concentrations reveals an increase of Si after HTA probably due to in-diffusion from the SiC substrate. However, C concentration reduces considerably with HTA that points to an efficient carbon removal process (i.e., CO formation).
Highlights
Despite a comparatively low lattice mismatch, the epitaxial growth of AlN on 4H–SiC results in a high dislocation density and suffers from a strong tendency to form small pits.3,4 Different approaches to improve the structural quality of AlN on SiC have been reported, mostly based on high-temperature growth in combination with a proper substrate treatment.5,6 As published by Chen et al.,7 a structurally improved
Epitaxial growth was carried out in a modified AIX2600G3HT “planetary” and a vertical closed-coupled showerhead (CCS) Metalorganic Vapor Phase Epitaxy (MOVPE) system, both configured for high-temperature growth
The high-temperature setup of the CCS system allows for a surface temperature of Ts = 1350 ○C, which is about 150 K higher compared to the temperature routinely achieved in the planetary system (Ts ∼ 1200 ○C)
Summary
Despite a comparatively low lattice mismatch, the epitaxial growth of AlN on 4H–SiC results in a high dislocation density (typically above 109 cm−2) and suffers from a strong tendency to form small pits.3,4 Different approaches to improve the structural quality of AlN on SiC have been reported, mostly based on high-temperature growth in combination with a proper substrate treatment.5,6 As published by Chen et al.,7 a structurally improved. The effect of high-temperature face-to-face annealing of Metalorganic Vapor Phase Epitaxy (MOVPE)-grown AlN layers on 4H–SiC substrates is investigated. High-temperature treatment at 1700 ○C for 3 h results in the removal of these pits [Fig. 1(b)] without changing the step-terrace structure of the surface.
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