Increased thermal conductivity of free-standing low-dislocation-density GaN films

1 Introduction GaN-based wide-band gap materials continue to attract significant attention as promising candidates for the next generation of microwave communication systems and optoelectronic devices [1–3]. For all envisioned applications of GaN materials, it is important to effectively remove the generated heat. Thus, the thermal conductivity K value of GaN is a very important characteristic. K varies with the crystal quality and the growth methods [4, 5]. The conventional growth methods such as metalorganic vapor phase epitaxy (MOVPE) growth of GaN films on sapphire or SiC substrates with AlN or GaN buffer layers usually result in a high threading dislocation density and stress, due to the lattice mismatch and differences in the thermal expansion coefficient between GaN and the non-native substrate. Dislocations limit the thermal conductivity [6] and electron mobility [7]. Increased thermal resistance of the structure and traps lead to degradation of the GaN-based transistor performance. A very recently developed technique for the growth of free-standing GaN films (substrates), using the hydride vapor phase epitaxy (HVPE), allows one to fabricate GaN films with much lower threading dislocation density [8, 9]. The low dislocation densities, characteristic of HVPE