Intersubband Transitions in InAs/AlSb Quantum Wells
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Intersubband Transitions in InAs/AlSb Quantum Wells J. Li, 1) K. Kolokolov, 1) C. Z. Ning, 1) D. C. Larraber, 2) G. A. Khodaparast, 2) J. Kono, 2) K. Ueda, 3) Y. Nakajima,3)S. Sasa, 3) and M. Inoue3) 1)
Center for Nanotechnology, NASA Ames Research Center, Moffett Field, CA 94035 Department of Electrical and Computer Engineering, Rice University, Houston, TX 77005 3) Department of Electrical Engineering, Osaka Institute of Technology, Osaka, Japan 2)
ABSTRACT We have studied intersubband transitions in InAs/AlSb quantum wells experimentally and theoretically. Experimentally, we performed polarization-resolved infrared absorption spectroscopy to measure intersubband absorption peak frequencies and linewidths as functions of temperature (from 4 K to room temperature) and quantum well width (from a few nm to 10 nm). To understand experimental results, we performed a self-consistent 8-band k⋅p band-structure calculation including spatial charge separation. Based on the calculated band structure, we developed a set of density matrix equations to compute TE and TM optical transitions self-consistently, including both interband and intersubband channels. This density matrix formalism is also ideal for the inclusion of various many-body effects, which are known to be important for intersubband transitions. Detailed comparison between experimental data and theoretical simulations is presented.
INTRODUCTION Antimonide-based quantum wells formed by three nearly lattice matched binaries, InAs, GaSb, AlSb, and their alloys have attracted much interest due to their wide range of potential applications in devices such as long AlSb wavelength detectors [1,2] and lasers [3]. Of special interest for optical applications are the extremely large conduction band offsets in InAs/AlSb heterostructures. Due to the large GaSb band gap difference and the special band-edge 7 lineups (see Fig. 1), the conduction band well 3 . 2 1 defined by the Γ−points of the two materials is as 8 . deep as 2 eV. Obviously, such a deep well offers great flexibility in realizing intersubband InAs 6 transitions (ISBTs) of a wide wavelength range, 5 . 4 . i.e., from the near-infrared (NIR) all the way to 4 . the far-infrared (FIR), or terahertz (THz) region. It was recently shown theoretically that a proper multi-well design using deep InGaAsAlAsSb-InP quantum wells allows completely FIGURE 1 Band gaps and their intersubband-based, optically-pumped THz lineups (unit is in eV)
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generation [4,5]. The advantage of such a scheme is that the pumping laser can be another compact semiconductor laser operating at 1.5 µm, instead of a CO2 laser commonly used for GaAs-based quantum wells. Similarly, InAs/AlSb quantum wells can be used for intersubband-pumped long-wave generation. As a first step towards realizing such a THz source, we have conducted a systematic study of optical transitions in InAs/AlSb quantum wells for a wide range of well widths. Specifically, we studied intersubband absorption spectra with varying temperatures and well widths. A la
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