  AlN is an ultra-wide bandgap semiconductor which has been developed for
applications including power electronics and optoelectronics. Thermal
management of these applications is the key for stable device performance and
allowing for long lifetimes. AlN, with its potentially high thermal
conductivity, can play an important role serving as a dielectric layer, growth
substrate, and heat spreader to improve device performance. However, the
intrinsic high thermal conductivity of bulk AlN predicted by theoretical
calculations has not been experimentally observed because of the difficulty in
producing materials with low vacancy and impurity levels, and other associated
defect complexes in AlN which can decrease the thermal conductivity. This work
reports the growth of thick AlN layers by MOCVD with an air-pocketed AlN layer
and the first experimental observation of intrinsic thermal conductivity from
130 K to 480 K that matches density-function-theory calculations for single
crystal AlN, producing some of the highest values ever measured. Detailed
material characterizations confirm the high quality of these AlN samples with
one or two orders of magnitude lower impurity concentrations than seen in
commercially available bulk AlN. Measurements of these commercially available
bulk AlN substrates from 80 K to 480 K demonstrated a lower thermal
conductivity, as expected. A theoretical thermal model is built to interpret
the measured temperature dependent thermal conductivity. Our work demonstrates
that it is possible to obtain theoretically high values of thermal conductivity
in AlN and such films may impact the thermal management and reliability of
future electronic and optoelectronics devices.
