Abstract
Low temperature photoluminescence (PL) from InP1−xBix thin films with Bi concentrations in the 0–2.49% range reveals anomalous spectral features with strong and very broad (linewidth of 700 nm) PL signals compared to other bismide alloys. Multiple transitions are observed and their energy levels are found much smaller than the band-gap measured from absorption measurements. These transitions are related to deep levels confirmed by deep level transient spectroscopy, which effectively trap free holes and enhance radiative recombination. The broad luminescence feature is beneficial for making super-luminescence diodes, which can theoretically enhance spatial resolution beyond 1 μm in optical coherent tomography (OCT).
Highlights
As Bi concentration increases, the InPBi peak moves toward low angles and becomes narrow with a FWHM decreasing to 46 arcsec, revealing good crystal quality for such a thin layer
Bi concentration are different from those found in GaAsBi42 and GaSbBi21 where PL peak follows the band gap reduction for small amount of incorporated Bi composition
Similar results were reported in Bi-doped GaP45,46 and InP47 where sharp PL peaks close to the band gap of the host materials together with a broad band lying within the 250 meV below the band gap are clearly observed at low temperatures
Summary
When only doped with 0.3% Bi, a broad InPBi layer peak with a FWHM of 189 arcsec emerges to the left of the InP substrate peak. As Bi composition increases, the band edge of InPBi shifts to longer wavelengths revealing a reduction of the band gap energy.
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