Abstract
Time-resolved ARPES makes it possible to directly visualize the band dispersion of photoexcited solids, as well as to study its time evolution on the femtosecond time scale. In this article, we show how this technique can be used to monitor the ultrafast hot carrier dynamics and the conduction band dispersion in two typical monochalcogenide semiconductors: direct band gap, n-type indium selenide and indirect band gap, p-type germanium selenide. With this approach, one can directly estimate the effective electron masses of these semiconductors. Moreover, the dynamics of hot electrons in the two semiconductors are analyzed and compared. Our findings provide valuable information for the use of monochalcogenide semiconductors in future optoelectronic devices.
Highlights
The electronic structure is a unique characteristic of a crystalline solid and encodes crucial information that determines the material’s electrical, magnetic and optical properties
Time-Resolved angle resolved photoemission spectroscopy (ARPES), where photoemission spectroscopy is performed in a pump– probe configuration using ultrafast light pulses, makes it possible to extend to the excited states all the advantages of this method, providing the time evolution of the non-equilibrium system, E = E (k, t )
The electron effective mass is extracted from the parabolic dispersion and the time constant of the decay process is obtained by exponential fittings
Summary
The electronic structure is a unique characteristic of a crystalline solid and encodes crucial information that determines the material’s electrical, magnetic and optical properties. In indirect band gap semiconductors, the radiation recombination is far slower compared to direct band gap, as the absorption or emission of phonons need to be involved in the process, which is not suitable for light emission devices [7, 8] In anisotropic semiconductors such as black phosphorus, the dispersions of conductions band along each high symmetric directions are significantly different, which corresponds to giant electron effective mass differences, and the mobility is highly direction dependent [9, 10]. Article we show how time-resolved ARPES can be used to investigate the photoexcited states in n-type InSe and p-type GeSe, and directly observe the dispersion of their conduction band and the hot carrier dynamics. The study of the photoexcited states presented in this work provides important information for further applications of InSe and GeSe in novel optical and optoelectronic devices
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