pISSN 0374-4914 eISSN 2289-0041

## Research Paper

New Physics: Sae Mulli 2016; 66: 472-477

Published online April 29, 2016 https://doi.org/10.3938/NPSM.66.472

## Study of the Characteristics of Quantum Cascade Lasers Employing a Tapered-active Region

Byeong Min AHN1, Jae Cheol SHIN*1, Yo han LEE2

1 Department of Physics, Yeungnam University, Gyeongsan 38541, Korea

2 Department of Sustainable Development, Yeungnam University, Gyeongsan 38541, Korea

Correspondence to:jcshin@yu.ac.kr

Received: December 14, 2015; Revised: January 18, 2016; Accepted: January 25, 2016

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

### Abstract

Conventional quantum cascade lasers (QCLs) are composed of a superlattice structure with identical compositions of quantum wells and barriers. In this structure, the energy difference between the upper laser state and the upper energy states leads to a significant leakage current from the upper laser state to the continuum band at room temperature. As a result, the operating characteristics ($i.e.$, T$_{0}$ and T$_{1}$) of QCLs at roon temperature are poor. In order to suppress carrier leakage in the active region, we suggest a QCL structure employing a tapered-active region (TA). Importantly, the alloy composition of the quantum wells and barriers are varied in this structure. In order to compare the operating characteristics of conventional QCL’s at room temperature with those of TA QCLs, we have examined the leakage current density at various temperatures by using a K$\cdot$P simulation. A significant reduction in the carrier leakage is found for the TA QCL structure. The reduction in the carrier leakage may improve the output power and the wallplug efficiency of the QCL during room-temperature, continuous-wave

Keywords: Quantum well, Mid-infrared, Tapered-active region, Quantum cascade laser