超低温高电场下GaAs的电子太赫兹功耗谱的研究

Terahertz power dissipation spectra of electrons in bulk GaAs under high electric fields at low temperature

利用自由空间太赫兹电光取样方法,测量了在高电场下,GaAs中受飞秒激光脉冲激发的电子所辐射出的太赫兹电磁波,发现从样品中辐射出的和电子加速度成正比的太赫兹电磁波电场强度ETHz(t),表现出双极特性.通过分析GaAs中辐射出的太赫兹电磁波的傅里叶变换谱,首次实验上得到在阶跃电场下的GaAs的电子太赫兹功耗谱.研究发现,当电场小于50kV/cm时,由电子谷间散射引起的负功耗(即增益)的截止频率νc,随着电场的增大而增大;当电场大于50kV/cm时,负功耗的截止频率νc开始在750GHz(10K)附近饱和.

By using the free-space terahertz（THz）electro-optic（EO）sampling technique,the THz electromagnetic wave waveforms emitted from intrinsic bulk GaAs photo-excited by femto-second laser pulses under strong bias electric fields up to 300 kV/cm were recorded.From the experimental data,we can clearly see the THz electromagnetic wave emission waveforms,ETHz（t）,which are proportional to the acceleration/deceleration of electrons,have a bipolar feature.Power dissipation spectra of electrons for step-function-like input electric fields have been obtained by calculating Fourier spectra of the measured THz traces.The cutoff frequency,νc,for negative power dissipation（i.e.,gain）due to intervalley transfer is found to gradually increase with increasing bias electric fields,F0,for F0 〈 50 kV/cm and saturate at 750 GHz above ～50 kV/cm at 10 K.