
68 Gallium Nitride (GaN): Physics, Devices, and Technology
substrates have also been used for the demonstration of green lasers [29,30]. For high-
power operations, the thermal conductivity of the substrate is expected to be an impor-
tant design issue and the relatively poor thermal conductivity of sapphire (kSapp =
0.35 W/cm-K) is expected to limit the device output power [7,31]. For the production
of LEDs, industries are now using 150- mm-diameter sapphire as a substrate for the
growth of GaN LED structure using laser lift-off technique [32]. SiC on the other
hand, has good thermal conductivity (k
SiC
= 4.9 W/cm-K) and is an obvious choice