||Nahid Akhter Jahan, Hitoshi Iijima, Claus Hermannstädter, Thomas J. Rotter, Pankaj Ahirwar, Ganesh Balakrishnan, Hidekazu Kumano, Ikuo Suemune
The optical behavior of InGaSb/GaSb QWs has recently attracted attention due to the narrow band-gap properties, high carrier mobility and applications in the infrared spectral region. As a resut of the low temperature GaSb band gap of 0.81 meV (1.53 µm), ternary InGaSb/AlGaSb heterostructures lattice matched on GaSb substrates are suitable to tailor wavelengths around 1.55 µm for usage in silica based fibre communication. Although wavelength-tunable quantum well long wavelength lasers are applicable in gas sensing, phase shifting interferometry, optical detectors, etc., reports on fundamental optical properties of InGaSb/AlGaSb heterostructures are not yet found prolific in number. Considering these aspects, the band structure of strained InGaSb/AlGaSb QWs, as well as optical properties and quantum confinement was examined in this work. The temperature dependent photoluminescence (PL) was measured to study the optical properties of InxGa1-xSb QWs for two different Indium concentrations. From the PL temperature dependence, the thermal quenching energy was found to be around 45 meV by fitting the measurement data with the Arrhenius equation. Based on the measured low temperature exciton recombination energies, the band structure and confinement were calculated by solving the Schroedinger equation for a finite potential well with a small valance band (VB) offset. The theoretical treatment of the strained QWs resulted in a strain contribution of -72 meV to the VB(heavy-holes), measured relative to the VB maximum at zero-strain. Including this band deformation potential and the measured 45 meV activation energy as input parameters, the confinement energy calculation results in a weak hole confinement energy and a thin InGaSb well of around 3 nm width along with a small VB offset. The emphasis on the assumption of a small VB offset comes with the key issue of the small activation energy which is suitably explained by the thermal escape of the single carrier holes from the QW to the barrier. To approve the composition and the calculated well thickness, X-ray diffraction measurements were carried out to precisely characterize the epitaxial layer structure. Both InxGa1-xSb QWs of 32% and 36% indium concentration exhibit a thin well width of around 3nm, which is in excellent agreement with the calculations. The InGaSb QW exhibits 1.52 µm photon emission at 10 K, which is desirable for fiber optical communication, and has the ability to be tuned to longer wavelengths by increasing the temperature. We demostrated a small thickness of the QWs and a small activation energy of 45 meV which is explained by the hole carrier escape because of weak confinement and small VB offset. The next target is to analyze the efficiency of InGaSb/AlGaSb QWs using time resolved spectroscopy.