Transverse effective charge and its pressure dependence in GaN single crystals

The pressure dependence of the A{sub 1}(TO) and A{sub 1}(LO)thinsp phonon modes of bulk, single crystals of wurtzite GaN has been measured by Raman scattering in a diamond-anvil cell up to 40 GPa. The measured phonon frequencies have been used to determine the LO and TO phonon-mode Gr{umlt u}neisen parameters and also the value of effective transverse charge e{sub T}{sup {asterisk}}=2.6 and its pressure derivative de{sub T}{sup {asterisk}}/dP={minus}2.4{times}10{sup {minus}3} GPa{sup {minus}1}. The experimentally obtained values are compared with results of calculations by means of tight-binding formalism combined with {ital ab initio} linear muffin-tin orbital calculations. {copyright} {ital 1999} {ital The American Physical Society}