中国激光, 2010, 37 (3): 658, 网络出版: 2010-03-11
砷化镓内电子谷间散射引起的增益
Electrons Intervalley Transfer Gain in Bulk GaAs
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
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。
Abstract
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.
倪争技, 陈麟, 王淑玲, 张大伟, 何波涌, 朱亦鸣. 砷化镓内电子谷间散射引起的增益[J]. 中国激光, 2010, 37(3): 658. Ni Zhengji, Chen Lin, Wang Shuling, Zhang Dawei, He Boyong, Zhu Yiming. Electrons Intervalley Transfer Gain in Bulk GaAs[J]. Chinese Journal of Lasers, 2010, 37(3): 658.