Realization of High-Performance and Farinfrared/Teraherz Quantum Cascade Lasers through Electron-Scattering Control

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Control of electron scattering is a key to achieve high-performance and farinfrared/terahertz quantum cascade lasers (QCLs) which are expected as light sources applicable to environmental gas monitoring and life science. Information on the electron scattering can be obtained by investigating the line enhancement factor α and relative intensity noise (RIN) of QCLs. Measurement of α provided us the knowledge of the non parabolicity of subbands in the conduction band and the Bloch gain. We could gain information on nonradiative relaxation time through the measurement of RIN dependence on optical output power and temperatures. We also analyzed a diagonal transition miniband structure for realizing farinfrared/terahertz QCLs. Since electron-electron scattering is proportional to the fourth power and optical transition the square of the overlap of wave functions, it is possible to reduce electron-electron scattering by using the diagonal transition.