多晶碲化锌薄膜载能子超快动力学实验研究  

Experimental study of ultrafast carrier dynamics in polycrystalline Zn Te nanofilm

作　　者：贾琳[1] 唐大伟[2] 张兴[1] 

机构地区：[1]清华大学航天航空学院,热科学与动力工程教育部重点实验室,北京100084 [2]中国科学院工程热物理研究所,北京100190

出　　处：《物理学报》2015年第8期327-331,共5页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:51206094,51327001,51336009)资助的课题~~

摘　　要：利用双波长飞秒激光抽运-探测实验方法测量了掺氮多晶Zn Te薄膜在飞秒激光加热情况下载能子超快动力学过程.采用包含电子弛豫过程和晶格加热过程的理论模型拟合实验数据,二者符合得很好.拟合得到10 ps以内影响掺氮多晶Zn Te薄膜表面超快反射率变化的三个弛豫过程的时间常数均为亚皮秒量级.其中,正振幅电子弛豫过程是由电子-光子相互作用引起的载流子扩散和带间载流子冷却过程,负振幅电子弛豫过程是由缺陷造成的光激载能子的俘获效应引起的,晶格加热过程主要通过电子-声子耦合过程进行的.Zinc telluride, due to its direct band gap and broadband light absorption, has the good application prospects in terahertz devices, solar cells, waveguide devices, and green light emitting diodes. In the photovoltaic field, it is possible to further improve the photoelectron conversion efficiency of multi-junction tandem solar cells by combining zinc telluride with III-V semiconductors. Ultrafast photo-excited carrier dynamics is fundamental to understand photoelectron conversion process of nanofilm solar cells. In this study, the ultrafast energy carrier dynamics of N-doped polycrystalline zinc telluride is investigated by using the femtosecond laser two-color pump-probe method at room temperature. The polycrystalline zinc telluride nanofilm is grown on a 500 ~m GaAs （001） substrate via molecular beam epitaxy and doped by using a nitrogen ratio frequency plasma cell. The laser pulses with a central wavelength of 800 nm are divided into pump beam and probe beam by a beam splitter, after which the pump beam passes through a bismuth triborate crystal and its frequency is doubled to 400 nm. The 400 nm pump beam and 800 nm probe beam are focused on the sample collinearly through the same objective lens. Photo-excited carriers will be generated since the excitation photon energy of 400 nm pump beam （3.1 eV） is higher than the band gap of zinc telluride （~ 2.39 eV）. The experimental data are analyzed by using the theoretical fitting model which includes energy relaxation processes of electrons and lattice, and the theoretical curves are consistent well with the experimental data. The fitted results show that the three dominated relaxation processes which affect the initial reflectivity recovery are in sub-picosecond time regime. The positive amplitude electron relaxation process is attributed to inter-band carrier cooling and carrier diffusion through electron-photon interactions, and the deduced decay time of this positive amplitude electron relaxation process is about 0.75 ps. The negative amplitude elect

关 键 词：碲化锌 多晶 飞秒激光 载能子 

分 类 号：O484[理学—固体物理]