Determination of the Temperature Dependent Thermal Expansion Coefficients of Bulk AlN by HRXRD

Abstract

Aluminum nitride is a promising substrate material due to its special characteristics. Because of its large band gap of 6.2 eV, AlN could be used for the realization of optoelectronic devices with an emission in the near to mid-UV region. Possible usages are the puriflcation of water or data storage. Furthermore, AlN is an insulator and has a high thermal conductivity, so it can be used as a substrate for high power and high frequency devices. The hardness also results in high sound velocity, which is useful for the construction of surface acoustic wave (SAW) devices, which are used in communication devices or as sensors. A realization of all these applications fails due to lack of substrates of su‐cient size and quality. Because of the challenging production, which is only possible from vapor phase, up to now only few companies ofier substrates in a reasonable quality. For the production of (opto-)electronic devices, usually epitaxial methods are used, which operate at high temperatures. A big problem is the bending and cracking of the deposited layers, caused by the difierent lattice constants of the used materials, which lead to an intrinsic stress. Furthermore, the thermal expansion can cause additional stress which has to be considered. Hence it is of technological interest to know the thermal behavior of AlN, which will play an increasing role in optoelectronics.