Abstract
AbstractEarth‐abundant and environmentally friendly semiconductors offer a promising path toward low‐cost mass production of solar cells. A critical aspect in exploring new semiconducting materials and demonstrating their enhanced functionality consists in disentangling them from the artifacts of defects. Nanowires are diameter‐tailored filamentary structures that tend to be defect‐free and thus ideal model systems for a given material. Here, an additional advantage is demostrated, which is the determination of the band structure, by performing high energy and spatial resolution electron energy‐loss spectroscopy in aloof and inner beam geometry in a scanning transmission electron microscope. The experimental results are complemented by spectroscopic ellipsometry and are excellently correlated with first principles calculations. This study opens the path for characterizing the band structure of new compounds in a non‐destructive and prompt manner, strengthening the route of new materials discovery.
Highlights
Earth-abundant and environmentally friendly semiconductors offer a promsynthesize the compound and to demonstrate the functionality
Considering that the size of Zn3P2 nanowire used in this study (Figure 2c) is significantly higher than the Bohr radii for Zn3P2, no quantum confinement effects are expected,[55] and the whole system can be treated from bulk material perspective
Electronic structure investigations of Zn3P2 were performed by valence electron energy loss spectroscopy (VEELS) and spectroscopic ellipsometry
Summary
We move to demonstrate the use of VEELS on Zn3P2 nanowires for a complete determination of the electronic band structure. Zn3P2 is a tetragonally structured semiconductor (space group P42/nmc (D415h)) with a direct bandgap at 1.5 eV, high absorption coefficient of 104–105 cm−1, and carrier diffusion lengths of ≈10 μm.[29,30,31,32,33,34,35] Current record solar cells have efficiencies of up to 6%,[36] which is well below their theoretical limit (>30%),[37] illustrating the improvement potential of this material.[37] While recent breakthrough in synthesis of highly crystalline Zn3P2 using innovative nanoscale methods (e.g., selective area epitaxy)[35,38,39] have rekindled the interest in the material, major limitations related to controllable optoelectronic properties[31,32,34,40,41,42,43,44,45,46,47] and device design still need to be resolved This is the reason why precise determination of the electronic properties of Zn3P2 is of uttermost importance. This includes numerically calculating the function Re[1/ε(ω)] from Im[−1/ε(ω)] by using the following relation:
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