Hot electron cooling in InSb probed by ultrafast time-resolved terahertz cyclotron resonance

TL;DR

This study introduces a time-resolved magneto-THz spectroscopy technique to measure electron effective mass changes in InSb, revealing rapid electron cooling and effective mass reduction within 200 ps after photoexcitation.

Contribution

The paper presents a novel ultrafast magneto-THz spectroscopy method capable of measuring cyclotron effective mass dynamics on a picosecond scale in semiconductors.

Findings

Electron effective mass decreases from 0.032m_e to 0.017m_e within 200 ps.

Measured effective mass variation aligns with ab initio conduction band non-parabolicity predictions.

Technique enables separation of charge-carrier cooling effects from recombination in conductivity measurements.

Abstract

Measuring terahertz (THz) conductivity on an ultrafast time scale is an excellent way to observe charge-carrier dynamics in semiconductors as a function of time after photoexcitation. However, a conductivity measurement alone cannot separate the effects of charge-carrier recombination from effective mass changes as charges cool and experience different regions of the electronic band structure. Here we present a form of time-resolved magneto-THz spectroscopy which allows us to measure cyclotron effective mass on a picosecond time scale. We demonstrate this technique by observing electron cooling in the technologically-significant narrow-bandgap semiconductor indium antimonide (InSb). A significant reduction of electron effective mass from 0.032$m_\mathrm{e}$ to 0.017$m_\mathrm{e}$ is observed in the first 200ps after injecting hot electrons. Measurement of electron effective mass in InSb as a function of photo-injected electron density agrees well with conduction band non-parabolicity predictions from ab initio calculations of the quasiparticle band structure.