An indirectly pumped terahertz quantum cascade laser with low injection coupling strength operating above 150 K

• Main Authors: Razavipour, S. G. (Author), Dupont, E. (Author), Fathololoumi, S. (Author), Lindskog, M. (Author), Wasilewski, Z. R. (Author), Aers, G. (Author), Laframboise, Sylvain R. (Author), Wacker, A. (Author), Ban, D. (Author), Liu, H. C. (Author), Chan, Chun Wang Ivan (Contributor), Hu, Qing (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science (Contributor), Massachusetts Institute of Technology. Research Laboratory of Electronics (Contributor)
• Format: Article
• Language: English
• Published: American Institute of Physics (AIP), 2014-05-15T19:32:28Z.
• Subjects: Article
• Online Access: Get fulltext

We designed and demonstrated a terahertz quantum cascade laser based on indirect pump injection to the upper lasing state and phonon scattering extraction from the lower lasing state. By employing a rate equation formalism and a genetic algorithm, an optimized active region design with four-well GaAs/Al[subscript 0.25]Ga[subscript 0.75]As cascade module was obtained and epitaxially grown. A figure of merit which is defined as the ratio of modal gain versus injection current was maximized at 150 K. A fabricated device with a Au metal-metal waveguide and a top n[superscript +] GaAs contact layer lased at 2.4 THz up to 128.5 K, while another one without the top n[superscript +] GaAs lased up to 152.5 K ( 1.3ℏω/k[subscript B] ). The experimental results have been analyzed with rate equation and nonequilibrium Green's function models. A high population inversion is achieved at high temperature using a small oscillator strength of 0.28, while its combination with the low injection coupling strength of 0.85 meV results in a low current. The carefully engineered wavefunctions enhance the quantum efficiency of the device and therefore improve the output optical power even with an unusually low injection coupling strength.