The characteristic emission from tail states below the bandgap of GaAsBi/GaAs quantum wells is studied using photoluminescence spectroscopy over a 10–300 K temperature range and a 0.1–1000 mW pump power range. The tail states exhibit two characteristic energies: A deeper one that is temperature independent at 29 meV and one nearer to bandgap that is temperature dependent, broadening from 17 meV at 10 K–29 meV at room temperature. The tail states are thought to originate from localization of the Bi states and disorder effects due to alloy fluctuations and clustering on the group-V sublattice.
The optical properties of bulk InAs0.936Bi0.064 grown by molecular beam epitaxy on a (100)-oriented GaSb substrate are measured using spectroscopic ellipsometry. The index of refraction and absorption coefficient are measured over photon energies ranging from 44 meV to 4.4 eV and are used to identify the room temperature bandgap energy of bulk InAs0.936Bi0.064 as 60.6 meV. The bandgap of InAsBi is expressed as a function of Bi mole fraction using the band anticrossing model and a characteristic coupling strength of 1.529 eV between the Bi impurity state and the InAs valence band. These results are programmed into a software tool that calculates the miniband structure of semiconductor superlattices and identifies optimal designs in terms of maximizing the electron-hole wavefunction overlap as a function of transition energy. These functionalities are demonstrated by mapping the design spaces of lattice-matched GaSb/InAs0.911Sb0.089 and GaSb/InAs0.932Bi0.068 and strain-balanced InAs/InAsSb, InAs/GaInSb, and InAs/InAsBi superlattices on GaSb. The absorption properties of each of these material systems are directly compared by relating the wavefunction overlap square to the absorption coefficient of each optimized design. Optimal design criteria are provided for key detector wavelengths for each superlattice system. The optimal design mid-wave infrared InAs/InAsSb superlattice is grown using molecular beam epitaxy, and its optical properties are evaluated using spectroscopic ellipsometry and photoluminescence spectroscopy.
Articles you may be interested inAlloying bismuth with InAs provides a ternary material system near the 6.1 Å lattice constant, which covers the technologically important mid-and long-wavelength infrared region. One challenge for this material system is that it is not straightforward to incorporate bismuth into the bulk InAs lattice, since bismuth has a tendency to surface-segregate and form droplets during growth. In this work, the conditions for InAsBi growth using molecular beam epitaxy are explored. A growth window is identified (temperatures կ 270 C, V/III flux ratios 0.98 խ As/In խ 1.02, and Bi/In ffi 0.065) for droplet-free, high-quality crystalline material, where InAsBi layers with compositions of up to 5.8% bismuth (nearly lattice-matched to GaSb) are attained. The structural quality of InAsBi bulk and quantum well samples is evaluated using x-ray diffraction and transmission electron microscopy. The optical quality is assessed using photoluminescence, which is observed from quantum well structures up to room temperature and from thick, low Bi-content bulk layers at low temperatures. Bismuth is also used as a surfactant during the growth of InAs/InAsSb superlattices at 430 C where it is observed that a small bismuth flux changes the surface reconstruction of InAs from (2Â1) to (1Â3), reduces the sticking coefficient of antimony, results in a slight increase in photoluminescence intensity, does not significantly incorporate, and does not alter the surface morphology.
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