Characterization of the three-well active region of a quantum cascade laser using contactless electroreflectance

Abstract

Quantum cascade (QC) lasers with emission at wavelengths below 4 μm are difficult to achieve from conventional III-V materials systems lattice matched to GaAs and InP due to the limited conduction band offset (CBO) of those materials that results from the presence of intervalley scattering. The II-VI materials ZnCdSe/ZnCdMgSe, with a CBO as high as 1.12 eV and no intervalley scattering, are promising candidates to achieve this goal. Using molecular beam epitaxy (MBE), the authors grew a QC laser structure with a three-well active region design made of ZnCdSe and ZnCdMgSe multilayers closely lattice matched to InP. A test structure, which contains only the active region of the QC laser separated by quaternary barrier layers, was also grown. The test structure was characterized by contactless electroreflectance (CER). Photoluminescence measurements and a model based on the transfer matrix method were used to identify the CER transitions. The energy levels obtained for the test structure were then used to predict the Fourier transform infrared (FTIR) absorption spectrum of the QC laser structure. Excellent agreement between the predicted values based on the test structure and the experimental FTIR absorption peaks of the full QC laser structure was observed.