Unraveling of free carrier absorption for terahertz radiation in heterostructures

TL;DR

This paper clarifies how free carrier absorption relates to intersubband transitions in semiconductor heterostructures, demonstrating that accurate modeling of these transitions suffices to simulate THz device absorption.

Contribution

It provides a combined numerical and analytical analysis showing the evolution of free carrier absorption from intersubband transitions in heterostructures with many wells.

Findings

Absorption integral matches the f-sum rule.

Proper intersubband transition treatment suffices for THz absorption simulation.

Absorption behavior transitions with increasing number of wells.

Abstract

The relation between free carrier absorption and intersubband transitions in semiconductor heterostructures is resolved by comparing a sequence of structures. Our numerical and analytical results show how free carrier absorption evolves from the intersubband transitions in the limit of an infinite number of wells with vanishing barrier width. It is explicitly shown that the integral of the absorption over frequency matches the value obtained by the f-sum rule. This shows that a proper treatment of intersubband transitions is fully sufficient to simulate the entire electronic absorption in heterostructure THz devices.