This indicates that the internal interface between the two GaAsBi regions of different Bi contents is highly perturbed and prevents the free flow of photo-excited carriers. At RT, the PL emission peaks are
dominated by band-to-band transitions, and hence, the PL peak energies can be tentatively correlated to the Bi composition of the material. From the AZD6244 relationship between band gap energy and Bi composition established by Usman et al.  the PL peaks of S100 at 1,108 and 980 nm correspond to a Bi content of approximately 5.1% and approximately 2.6%, respectively. Similarly, the main peak of S25 at 1,057 nm corresponds to a Bi content of approximately 4.2%. This indicates that the maximum Bi content of S100 is higher than S25, despite nominally identical flux ratios were used Fosbretabulin mw during growth. This discrepancy is believed to be due to an inherent error in the temperature calibration that resulted in S100 being grown approximately 15°C lower than S25 and not a result of the thinner overall layer thickness. Despite the difference in the absolute peak position, the RT-PL spectra of both samples exhibit a similar envelope comprising (1) a high-wavelength tail and (2) a lower wavelength shoulder. This asymmetric emission indicates that both
spectra are formed from the superposition of at least three individual PL peaks. It is therefore possible that the shape of the PL spectra corresponds to structural or compositional features that are present in both samples, whereas the distinct lower energy peak in S100 corresponds to a feature not present in S25. Structural and compositional TEM Protein kinase N1 In order to find an explanation of the PL spectra, TEM studies were carried out by diverse techniques. Low-magnification CTEM images acquired using different diffraction conditions sensitive to defects (not shown in this paper) revealed defect-free epilayers in the electron-transparent area of sample S25 and some isolated dislocations in sample S100. Thus, the RT-PL
intensity of both samples is nominally identical despite the presence of threading dislocations in S100; however, their presence at the internal-interface may explain the splitting of the PL peaks in S100. The physical origin of the each of the PL peaks requires further analysis. HAADF-STEM images were used to study the distribution of bismuth in the GaAsBi layers. see more Interpretation of this kind of image (also called Z-contrast images) is relatively straightforward, since the contrast is roughly proportional to the square of the atomic number at constant sample thickness [29, 30]. Hence, for the case of a ternary alloy where bismuth is the only variable element, brighter contrast should in principle be associated with higher Bi content. Z-contrast images (Figure 2a,b) showed uniform GaAs1−x Bi x layer widths in both samples, corresponding to the nominal ones.