Temperature effect on the coupling between coherent longitudinal phonons and plasmons in n- and p-type GaAs

TL;DR

This study investigates how temperature influences the coupling between LO phonons and plasmons in doped GaAs, revealing unexpected suppression of coherent oscillations in p-type at low temperatures due to carrier diffusion effects.

Contribution

It provides new insights into temperature-dependent phonon-plasmon coupling in GaAs, highlighting differences between n- and p-type doping and the impact of depletion layer dynamics.

Findings

Suppression of coherent oscillations in p-type GaAs at low temperature

Enhanced coupling in n-type GaAs with cooling

Cooling-induced elongation of depletion layer affects phonon-plasmon dynamics

Abstract

The coupling between longitudinal optical (LO) phonons and plasmons plays a fundamental role in determining the performance of doped semiconductor devices. In this work, we report a comparative investigation into the dependence of the coupling on temperature and doping in n- and p-type GaAs by using ultrafast optical phonon spectroscopy. A suppression of coherent oscillations has been observed in p-type GaAs at lower temperature, strikingly different from n-type GaAs and other materials in which coherent oscillations are strongly enhanced by cooling. We attribute this unexpected observation to a cooling-induced elongation of the depth of the depletion layer which effectively increases the screening time of surface field due to a slow diffusion of photoexcited carriers in p-type GaAs. Such an increase breaks the requirement for the generation of coherent LO phonons and, in turn, LO phonon-plasmon coupled modes because of their delayed formation in time.