Abstract
Boron (B) has the potential for generating an intermediate band in cubic silicon carbide (3C-SiC), turning this material into a highly efficient absorber for single-junction solar cells. The formation of a delocalized band demands high concentration of the foreign element, but the precipitation behavior of B in the 3C polymorph of SiC is not well known. Here, probe-corrected scanning transmission electron microscopy and secondary-ion mass spectrometry are used to investigate precipitation mechanisms in B-implanted 3C-SiC as a function of temperature. Point-defect clustering was detected after annealing at 1273 K while stacking faults, B-rich precipitates and dislocation networks developed in the 1573 - 1773 K range. The precipitates adopted the rhombohedral B13C2 structure and trapped B up to 1773 K. Above this temperature, higher solubility reduced precipitation and free B diffused out of the implantation layer. Dopant concentrations of \mathbf{10^{19}\:\mathrm{\mathbf{at.cm}}^{-3}}1019𝐚𝐭.𝐜𝐦−3 were achieved at 1873 K.
Highlights
An intermediate band (IB) in the energy band gap of a semiconductor allows photons with lower energy than the band gap to excite electrons from the valence to the conduction band, increasing the photocurrent generated [1]
Lattice images were indexed using fast Fourier transforms (FFT) and strain was evaluated by geometric phase analysis (GPA) using the FRWRtools plugin [15] implemented in Digital Micrograph (Gatan Inc)
Cross-sectional scanning transmission electron microscopy (STEM) images obtained directly after implantation and after annealing at 1273 K are shown in figure 1 together with the corresponding concentration profiles obtained by secondary-ion mass spectrometry (SIMS)
Summary
An intermediate band (IB) in the energy band gap of a semiconductor allows photons with lower energy than the band gap to excite electrons from the valence to the conduction band, increasing the photocurrent generated [1]. Due to the potential for enhanced efficiency in energy conversion, intermediate-band solar cells are promising candidates for the generation of photovoltaic devices. The hydrogen-like model with the values of permittivity and effective hole mass reported for 3C-SiC [5] estimates 1019 - 1020 at.cm−3 as the minimum concentration of shallow acceptors for their energy levels to merge into impurity bands. The two acceptor levels associated with B in SiC are rather deep Correlation of the microstructural observations with secondary-ion mass spectrometry (SIMS) data was used to evaluate B solubility
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