Boundary-enhanced momentum relaxation of longitudinal optical phonons in GaN
In this work,we studied the high-field electron transport properties in n-GaN charmels designed to have varied dimensions.The influence of the channel geometry on the high-field electron drifl velocities is discussed.High-field I-V curves were obtained by nanosecond pulsed technique on H-shape sample mounted in a 50 Ω matched circuit.The channels were divided into two groups:group A,with channel width (W) > 18 μrn and group B,with W< 5 am.It is observed that electrons in group B drift much faster than those in group A at high fields.Meanwhile,the electron temperature in group A is obviously higher than those in group B..Since the LO-phonon lifetime (τph) is much longer than the spontaneous LO-phonon emission time (~10 fs) in GaN,the LO phonons tend to accumulate to form hot phonons (HP) in GaN.From the perspective of momentum relaxation,it is found that the hottest-state HP scatter electron momentum most efficiently.Considering that the drift velocity of electrons in narrow channels is higher than that in wide ones,one can speculate that the boundary can affect the HP distribution at high fields.The boundary scattering can be induced by the specular or rough surface of the sample or some charged center arround the surface.Since HP exist in the form of a nonequilibrium state,this state tends to be destroyed by any kind of randomization scattering and returns to the equilibrium state.The experimental results of the energy loss rate as a function of the reciprocal Te and the calculated curves indicate that the equivalent τPh is shorter in group B with value of about 0.4 ps while rPh in Group A is around 1 ps.The obtained τb is about 0.67 ps.It is certain that the boundary scattering of HP can accelerate the transition of the HP system into the equilibrium lattice vibration system,and thus weaken the HP effect in GaN bulk layers.
N.Ma B.Shen F.J.Xu L.W.Lu L.Guo X.Q.Wang X.L.Yang
State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics,Peking University
国内会议
开封
英文
11-11
2012-11-07（万方平台首次上网日期，不代表论文的发表时间）