An extended density matrix model applied to silicon-based terahertz quantum cascade lasers

TL;DR

This paper introduces a comprehensive density matrix model for silicon-based terahertz quantum cascade lasers, enabling more accurate simulations of device performance and effects of interdiffusion, thus advancing design capabilities.

Contribution

It presents a generalized density matrix transport model that requires less prior knowledge of bandstructure, suitable for semi-automated design of Si-based QCLs.

Findings

Devices with 4-5 nm barriers yield highest optical gain.

Interdiffusion lengths up to 1.5 nm have minimal impact on performance.

The model extends beyond the rotating-wave approximation for better accuracy.

Abstract

Silicon-based terahertz quantum cascade lasers (QCLs) offer potential advantages over existing III-V devices. Although coherent electron transport effects are known to be important in QCLs, they have never been considered in Si-based device designs. We describe a density matrix transport model that is designed to be more general than those in previous studies and to require less a priori knowlege of electronic bandstructure, allowing its use in semi-automated design procedures. The basis of the model includes all states involved in interperiod transport, and our steady-state solution extends beyond the rotating-wave approximation by including DC and counter-propagating terms. We simulate the potential performance of bound-to-continuum Ge/SiGe QCLs and find that devices with 4-5-nm-thick barriers give the highest simulated optical gain. We also examine the effects of interdiffusion between Ge and SiGe layers; we show that if it is taken into account in the design, interdiffusion lengths of up to 1.5 nm do not significantly affect the simulated device performance.