The lifetimes of polar optical phonons are known to affect the electrical and thermal performance of gallium nitride (GaN) based devices. Utilizing the energy-time uncertainty relation, this study investigates these lifetimes using Raman spectroscopy for a series of samples having free carrier concentrations ranging from 1.24e18 to 3e17 cm−3. By measuring across the typical operating temperatures of these devices, the mechanisms responsible for scattering of 5 separate optical modes are elucidated. It is found that phonon-carrier interaction directly determines the lifetime of the polar optical A1(LO) mode while indirectly influencing the modes into which this longitudinal phonon decays, namely, E1 and A1(TO). Thus understanding the entire phonon energy cascade is vital both for management of the so called “hot phonon” effect as well as modeling of carrier-phonon interactions.
Role of interfacial mode coupling of optical phonons on thermal boundary conductance
