Temperature and doping dependence of phonon lifetimes and decay pathways in GaN

Abstract

The lifetimes of polar optical phonons are known to affect both the electrical and thermal performances of gallium nitride ͑GaN͒ based devices. Hence, understanding the dynamical behavior of these phonons in GaN is integral to the elucidation of carrier drift velocities, hot phonon effects, and temperature localization in these nitride semiconductors. To investigate this dynamic behavior, temperature dependent phonon lifetimes were acquired through utilization of the linewidth of the Raman response for GaN samples having various doping types and concentrations. The temperature dependent lifetimes of the four examined phonon modes were then correlated with the Klemens decay model modified to account for four-phonon processes to deduce the decomposition of the zone center phonons. A graphical method that maps this decomposition in the high symmetry directions of the Brillouin zone is also presented. From the variation in lifetime with free carrier concentration, dominant scattering mechanisms are subsequently found for each of four different phonon modes. It is observed that the phonon-carrier interaction directly determines the lifetimes of the polar optical A1 and E1͑LO͒ modes, while the transverse modes into which these longitudinal phonons decay are independent of this interplay. These results indicate that temperature localization likely arises due to the continual emission and reabsorption between the LO phonon modes and the free carriers rather than the persistence of lattice/carrier interaction throughout the entirety of the energy cascade.

Temperature‐dependent Raman investigation of CuInS2 with mixed phases of chalcopyrite and CuAu

“…(1) describe the contributions of the three‐ and the four‐phonon processes, which are proportional to T and T 2 at high temperature, respectively 24, 29. For the three‐phonon process, two models, namely, the Klemens and the Ridley model have been employed to fit the three‐phonon contribution 24–26, 30, 31. In a Klemens process, it is assumed that an optical phonon decays symmetrically into two acoustic phonons with same energy and opposite momentum, namely, x j = $\hbar \omega $ (0)/2 k B T 32.…”

InAlN‐barrier HFETs with GaN and InGaN channels

“…Fluctuation-based techniques [31,33,46] seem to be the most suitable for obtaining the required experimental data. It should be noted that, the dependence of hot-phonon lifetime on phonon temperature has been recently treated theoretically [47,48].…”

Negative differential resistance associated with hot phonons

“…1 The same is true of measurements of bandwidth, given the assumptions associated with the uncertainty principle. [2][3][4] Other techniques yield lifetimes that are averages over the range of wave vectors most strongly coupled to the hot electrons, typically 0 q 10 9 m À1 in GaN. Extrapolation of Raman results to this regime would be valid only if the lifetime was not a function of wave vector, but, as we will show, coupled-mode effects make such an extrapolation invalid.…”