D8 discover x

SEM was performed using a Quanta 3D FEG scanning electron microscope. TEM images, high-angle annular dark-field TEM images, SAED patterns, element mappings and EDX line-scan were carried out on a JEOL-2800 TEM/STEM system using gold grids. XPS was recorded using an AXIS Nova spectrometer (Kratos Analytical) equipped with a monochromatic Al Kα X-ray source (1487 eV, 15 mA emission current) and an inert ion gas gun for depth-profiling composition analysis as a function of etching time. For the core-level spectra, the binding energies were calibrated based on the C 1s feature located at 284.8 eV. The nuclear magnetic resonance (NMR) spectroscopy was performed on a Bruker 400 MHz NMR spectrometer. XRD were obtained using a Bruker D8 Discover X-ray diffractometer with Cu Kα radiation ( $\lambda =1.5418\AA$ ).

Photocurrent and XRD were used to estimate the device bandgap energies and Bi contents. A Bruker D8 Discover X-ray diffractometer was used to perform ω-2θ scans on each diode. The Bi contents were determined by fitting the XRD spectra using RADS Mercury software, in which the GaBi lattice constant was assumed to be 6.324 Å^{45 (link)}. Room-temperature photocurrent measurements were undertaken on devices using a tungsten-lamp and a monochromator, and the bandgap energy was deduced from this. The Bi content determined in this manner showed very good agreement with the theoretical curve in Fig. 1c taking into account the strain relaxation (as detailed in the Supplementary section), with an uncertainty in Bi composition of ± 0.1 %. Absorption coefficients were extracted by determining the quantum efficiency of the GaAsBi samples in the range > 900 nm assuming that the GaAs cladding layers were effectively transparent.