We study ultrafast relaxation of nonthermal electrons confined within the Γ valley of GaAs, based on the momentum-resolved transient electron distribution functions determined using time- and angle-resolved photoemission spectroscopy at 293 K. To elucidate the fundamental processes that lead to the electronic quasithermalization at the nonthermal regime of relaxation, the dynamics in both $p$- and $n$-type samples of GaAs are investigated. In $p$-type GaAs, photoinjected electrons form the electron ensembles quasiequilibrated only in the momentum space within 100 fs of excitation by the Coulomb interaction among photoinjected electrons. However, the ensembles maintain strong nonthermal populations in the energy space. They are quasithermalized only after certain time delays of a few hundred femtoseconds, which depend on the excess energy of photoinjected electrons. These features in $p$-type samples are not sensitively dependent on the excitation density in the range from $1.5\times {10}^{16}$ to $5\times {10}^{17}\mathrm{c}{\mathrm{m}}^{\text{–}3}$. On the other hand, in $n$-type samples, which include the cold electrons populated near the conduction-band minimum with the density of $\sim 1\times {10}^{18}\mathrm{c}{\mathrm{m}}^{\text{–}3}$, photoinjected electrons are quasithermalized within 170 fs of excitation. The main interaction for the fast quasithermalization is attributed to the inelastic scattering among the cold electrons and photoinjected electrons by a dynamics screened Coulomb interaction like the electronic thermalization in metals.

中文翻译：

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通过时间和角度分辨光电子能谱研究 GaAs Γ 谷中光注入非热电子的超快弛豫

我们研究了限制在 GaAs Γ 谷内的非热电子的超快弛豫，基于使用 293 K 的时间和角度分辨光电子能谱确定的动量分辨瞬态电子分布函数。 阐明导致电子准热化的基本过程在非热弛豫状态下，两者的动力学 $p$- 和 $n$研究了 GaAs 的 - 型样品。在$p$型 GaAs，光注入电子通过光注入电子之间的库仑相互作用形成仅在 100 fs 激发内的动量空间中准平衡的电子系综。然而，这些系综在能量空间中保持着强大的非热种群。它们仅在几百飞秒的特定时间延迟后准热化，这取决于光注入电子的过剩能量。这些特点在$p$- 型样品不敏感地依赖于范围内的激发密度 $1.5\times {10}^{16}$ 到 $5\times {10}^{17}\mathrm{C}{\mathrm{米}}^{\text{——}3}$. 另一方面，在$n$型样品，其中包括密度为导带最小值附近的冷电子 $～1\times {10}^{18}\mathrm{C}{\mathrm{米}}^{\text{——}3}$，光注入电子在激发的 170 fs 内准热化。快速准热化的主要相互作用归因于冷电子和光注入电子之间的非弹性散射，通过动力学筛选库仑相互作用，如金属中的电子热化。