Time-resolved differential reflectivity as a probe of on-resonance exciton dynamics in quantum wells
Time-resolved differential reflectivity as a probe of on-resonance exciton dynamics in quantum wells
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时间分辨微分反射率作为量子阱中共振激子动力学的探针
DOI：
10.1103/physrevb.67.165328
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发表时间：
2003
影响因子：
3.7
通讯作者：
S. Selci
中科院分区：
文献类型：
--
作者：
F. Fernandez;M. Righini;A. Franco;S. Selci
我们研究了利用时间分辨微分反射率来研究共振激发的量子阱激子的超快和复合动力学。我们使用飞秒激光脉冲在4 nm的${\mathrm{In}}_{0.1}{\mathrm{Ga}}_{0.9}\mathrm{As}上进行了广泛的时间分辨测量，|GaAs量子阱。适用于量子阱系统的简单考虑使我们能够将反射率的一般变化与跃迁振子强度的变化联系起来，而跃迁振子强度又与强泵浦光束产生的激子密度（粒子数反转）成比例。作为一个起点的时间演化的两个级别的系统下的共振激发，我们解释差分反射率测量的动态过程，范围从偏振退相（数百飞秒）辐射和非辐射复合（纳秒）。这些不同的动态过程跨越了四个数量级的时域，可以从一个单一的时间分辨差分反射率实验中提取。我们还发现，所观察到的时间衰减是相当敏感的初始（和冷）光生人口。我们发现，可以利用差分反射率信号的功率依赖性来获得激子饱和密度的估计，以及研究激子-激子散射和热化对总复合时间的作用。在低功率激发条件下，我们与微分反射率衰减的总激子复合寿命。作为温度的函数的寿命测量证实了这一分配，因为它们显示了在低温下的初始和准线性上升$（Tl70\mathrm{K}）$，随后在较高的温度下由于非辐射复合通道的主导地位下降。
We investigate the use of time-resolved differential reflectivity for the study of the ultrafast and recombination dynamics of resonantly excited quantum-well excitons. We illustrate the technique with extensive time-resolved measurements using femtosecond laser pulses on a 4-nm ${\mathrm{In}}_{0.1}{\mathrm{Ga}}_{0.9}\mathrm{As}|\mathrm{GaAs}$ quantum well. Simple considerations applicable to quantum-well systems allow us to relate a generic change in reflectivity to a change in transition oscillator strength, which in turn is proportional to the exciton density (population inversion) created by an intense pump beam. Having as a starting point the temporal evolution of a two-level system under resonant excitation, we interpret differential reflectivity measurements in terms of dynamical processes that range from polarization dephasing (hundreds of femtoseconds) to radiative and nonradiative recombination (nanoseconds). These various dynamical processes span over four orders of magnitude in the time domain and may be extracted from a single time-resolved differential reflectivity experiment. We also find that the observed temporal decays are quite sensitive to the initial (and cold) photogenerated population. We show that a power dependence of the differential reflectivity signal can be utilized to obtain estimates of the exciton saturation density as well as to study the role of exciton-exciton scattering and thermalization on the total recombination time. Under low-power excitation conditions, we relate the differential reflectivity decay to the total exciton recombination lifetime. Lifetime measurements as a function of temperature confirm this assignment as they show an initial and quasilinear rise at low temperatures $(Tl70\mathrm{K})$ followed by a decrease at higher temperatures owing to the dominance of nonradiative recombination channels.