Influence of surface passivation on ultrafast carrier dynamics and terahertz radiation generation in GaAs

TL;DR

This study investigates how surface passivation of GaAs affects ultrafast carrier behavior and enhances terahertz radiation, demonstrating significant improvements in device performance due to surface chemistry modifications.

Contribution

It provides new insights into the impact of (NH4)2S passivation on GaAs surface electric fields, carrier dynamics, and THz emission efficiency, combining experimental and simulation approaches.

Findings

Surface electric field reverses after passivation

Photoexcited electron conductivity doubles post-passivation

Passivation enhances THz emission power in photoconductive switches

Abstract

The carrier dynamics of photoexcited electrons in the vicinity of the surface of (NH4)2S-passivated GaAs were studied via terahertz (THz) emission spectroscopy and optical-pump THz-probe spectroscopy. THz emission spectroscopy measurements, coupled with Monte Carlo simulations of THz emission, revealed that the surface electric field of GaAs reverses after passivation. The conductivity of photoexcited electrons was determined via optical-pump THz-probe spectroscopy, and was found to double after passivation. These experiments demonstrate that passivation significantly reduces the surface state density and surface recombination velocity of GaAs. Finally, we have demonstrated that passivation leads to an enhancement in the power radiated by photoconductive switch THz emitters, thereby showing the important influence of surface chemistry on the performance of ultrafast THz photonic devices.