摘要
运用时域太赫兹波谱法,低温(10 K)高电场下本征砷化镓中受飞秒激光脉冲激发的电子所辐射出的太赫兹波被准确地测量出来。从样品中辐射出的和电子加速度/减速度成正比的太赫兹电磁波,表现出双极特性。通过分析砷化镓中辐射出的太赫兹波的傅里叶变换谱,在实验上得到阶跃电场下的砷化镓内因电子谷间散射而引起的增益极限频率,可以达到约750 GHz(10 K)。同时通过测量极限频率和温度的关系,发现极限频率是电子经由纵光学声子从L谷到Γ谷的散射能量弛豫过程所需要的时间决定的。通过理论计算电子在Γ谷的弹道加速、电子谷间散射和电子经由纵光学声子连续散射在Γ谷的弛豫等过程的时间得出的增益极限频率与实验值吻合得较好。
By using time-domain terahertz（THz） spectroscopy,the THz waveforms emitted from bulk GaAs photoexcited by femtosecond laser pulses under very high electric fields at 10 K have been recorded.It is clearly seen that the THz emission waveforms show a bipolar feature i.e.,an initial positive peak and a subsequent negative dip.Terahertz intervalley transfer gain under step-function-like input electric fields F has been obtained by calculating Fourier spectrum of the measured THz trace under various biased electric fields.We found it can reach 750 GHz for F 50 kV/cm at 10 K.Furthermore,from the temperature dependence of the cutoff frequency for the gain,it is found that the cutoff frequency is governed by the energy relaxation process of electrons from L to Γ valley via successive longitudinal-optical phonon emission.The estimated cutoff frequencies,at 10 K by considering the time for electrons ballistic acceleration in Γ valley,intervalley transfer,relaxation in Γ valley via longitudinal-optical phonon scattering match the experimental results very well.
出处
《中国激光》
EI
CAS
CSCD
北大核心
2010年第3期658-662,共5页
Chinese Journal of Lasers
基金
上海市教育委员会
上海市教育发展基金会晨光计划(09CG49)
曙光计划(08SG48)
上海市教育委员会科研创新项目(09YZ221)
上海高校选拔培养优秀青年教师科研专项基金(slg08005)
上海市委浦江人才计划(09PJ1407800)
上海市科技委员会项目(07DZ22026
08530707400
08ZR1415400
08DZ2272800)资助项目
关键词
光谱学
砷化镓
电子谷间散射
增益
时域太赫兹波谱法
非平衡载流子
spectroscopy
GaAs
electrons intervalley transfer
gain
time-domain terahertz spectroscopy
nonequilibrium carriers
