Electric-Field Ionization of Gallium Acceptors in Germanium Induced by Single-cycle Terahertz Pulses

TL;DR

This study investigates how single-cycle terahertz pulses can ionize gallium acceptors in germanium, revealing field-dependent ionization dynamics and supporting a tunneling model through spectroscopic measurements.

Contribution

It demonstrates the electric field ionization of acceptors using terahertz spectroscopy and models the process as direct field-assisted tunneling.

Findings

Decreased acceptor transition absorption with increasing field

Emergence of lower frequency absorption indicating ionization

Model accurately reproduces electric field dependence of hole density

Abstract

The electric field ionization of gallium acceptors in germanium was studied by using terahertz time-domain spectroscopy after single-cycle terahertz pulse excitation. As the peak electric field of the excitation pulse increases, the distinct absorptions due to acceptor transitions centered at 2.0 and 2.2 THz decrease, and simultaneously, absorption emerges in the lower frequency region. These behaviors clearly show that the terahertz pulse ionizes neutral acceptors. The electric field dependence of the released hole density is well reproduced by a model assuming direct field-assisted tunneling of acceptors.