Exploiting the P L2,3 absorption edge for optics: spectroscopic and structural characterization of cubic boron phosphide thin films

The transmission of cubic boron phosphide (c-BP) thin films, prepared by chemical vapor deposition (CVD), was evaluated near the phosphorous L2,3 and boron K absorption edge. The c-BP films were analyzed with transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES), to study their structural and chemical properties. The TEM analysis reveals that c-BP initially grows in islands. The merging of the P L2,3, P K and B K absorption edges culminates in a sharp absorption feature starting at 130 eV, showing that c-BP can be used in applications that require a relatively transparent material in the energy range just below that absorption feature. Due to experimental constraints the samples were grown at a temperature significantly below the temperature for optimal crystal growth. XANES analysis showed that, as a result of the reduced crystal quality, the intensities of the absorption transitions are reduced compared to those in high quality crystalline reference samples. Optimizing the quality of the BP films will increase the contrast in transmission across the absorption edge.