Observation of symmetrically decay of A1(longitudinal optical) mode in free-standing GaN bulk single crystal from Li3N flux method

Abstract

We report Raman analysis of A1(LO) (longitudinal optical) and E2(high) phonon lifetimes in a bulk GaN single crystal and their temperature dependence from 77 K to 770 K. Both the A1(LO) and E2(high) phonons in GaN were observed decaying primarily into two phonons of equal energy [Klemens model, P. G. Klemens, Phys. Rev. 148, 845 (1966)]. This is a rare example of a high-quality free-standing GaN bulk single crystal displaying abnormal A1(LO) phonon decay. These results will have significant impact on designing and understanding of GaN-based high-speed, high-power electric devices.

Redshift ofA1(longitudinal optical) mode for GaN crystals under strong electric field

“…6) It is believed that hot-phonon decay can be evaluated in terms of the LO phonon lifetime, which determines the hot-phonon effects, i.e., a sufficiently long LO phonon lifetime reduces the rate at which hot electrons lose energy and reduces the carrier mobility. [7][8][9] Electric field-induced Raman scattering, which allows us to probe the changes of the electric fields in space-charge layers at semiconductor surfaces and interfaces, has also been widely used to investigate the LO phonons of GaAs or CdS under a strong electric field (∼10 6 V=m), 10,11) but has been used rarely for GaN. Consequently, exploring the LO phonon property is crucial for understanding GaN, particularly under nonequilibrium conditions.…”

Photoluminescence Behaviors of Orange-Light-Emitting InGaN-Based Nanocolumns Exhibiting High Internal Quantum Efficiency (17–22%)

“…This temperature characteristic is considered to have resulted from the high indium composition in the NC samples, leading to the creation of crystal defects by an as-yet-unrecognized mechanism and increased fluctuation in the In composition. Here thermally activated carrier delocalization 14) and carrier diffusion, changes in the carrier lifetime, 15) carrier overflow from the QWs, and different Auger coefficients at different temperatures 16) would be related to this phenomenon. To clarify the emission mechanism, further study is needed, which is beyond the scope of this article.…”