Temperature dependence of the thermal expansion of AlN

The thermal expansion of wurtzite AlN bulk crystals grown by physical vapor transport was studied by high resolution x-ray diffraction in a temperature range from 20 to 1250 K. The temperature dependence of the derived anisotropic thermal expansion coefficients along the a- and c-directions could be well described over the entire temperature range within both the Debye model and the Einstein model. In comparison to GaN, larger expansion coefficients and higher characteristic temperatures have been found. The resulting thermal mismatch of AlGaN/GaN heterostructures are presented.