High-temperature annealing induced evolution of strain in AlN epitaxial films grown on sapphire substrates

Abstract

High-temperature (HT) annealing effects on the evolution of strain in AlN films grown on sapphire have been investigated. It is found that there is a significant transition behavior from tensile to compressive strain in AlN before and after HT annealing at an optimal temperature of 1700 °C. Based on a microstructural analysis, it is clarified that the HT annealing will result in the (1) disappearance of grains that account for the tensile stress before HT annealing, (2) generation of a new interface that has little influence on the lattice constant upper/below this interface, and (3) regular 8/9 arrangement of misfit dislocation at the AlN/sapphire interface that relieves almost all stress associated with lattice mismatch. It is thus deduced that the remnant compressive strain in AlN after HT annealing mainly comes from the cooling down process due to thermal mismatch between sapphire and AlN. This understanding of the annealing effect is certainly of great significance in AlN materials science and technology.

High‐Temperature Annealing of AlGaN

“…The XRC‐FWHM of the AlN 10–12 reflection decreases from 852 to 370 arcsec with increasing annealing temperature and therefore, despite of the AlGaN layer, behaves as usually observed for HTA of MOVPE‐grown AlN. [ 11,17 ] The trend of the 10–12 AlGaN XRC‐FWHM is not as clear. For annealing temperatures up to 1650 °C, it decreases from 767 to 545 arcsec, but increases to 580 arcsec for further increasing annealing temperature, indicating an increase in the twist component.…”

“…It is attributed to rearrangement of AlN at high temperatures and the thermal mismatch between AlN and sapphire. [ 7,17 ] For the highest temperature of 1705 °C, a significant Al mole fraction gradient is visible in the RSM by the shift and elongation of the AlGaN peak toward the AlN peak position along the dashed line in Figure 4b. The Al mole fraction increases to 0.80.…”

Temperature Dependence of Stress and Optical Properties in AlN Films Grown by MOCVD

“…The values of stress σ are calculated from the experimental peak positions ω obtained in this work by using the following Equation [ 39 ]: where the stress-shift coefficient κ has the value of 4.04 cm − 1 /GPa [ 40 ] and a stress-free position ω 0 is reported to be 657.4 cm − 1 for E 2 (high) [ 41 , 42 ]. The biaxial stress σ values associated with temperature are plotted in Figure 3 .…”

Carrier Velocity Modulation by Asymmetrical Concave Quantum Barriers to Improve the Performance of AlGaN-Based Deep Ultraviolet Light Emitting Diodes

“…Figure 1(a) shows the schematic structure of these two samples. Both of them are grown on a 1-um-thick annealed AlN buffer layer with a (0001) c-plane sapphire [14], [15], followed by a 0.5-um-thick AlN/AlGaN stress modulation multilayers and a Semiconductor Devices program is adopted in this study to conduct simulations [16], which can help to understand the inherent transport mechanism including the energy band, carrier injection behavior, and carrier distribution within the active region. And the parameter setting can be found in our previous work [9].…”