The bandgap value is obtained from the linear extrapolation of the rising part for each sample [16] and shown in Figure 3, where
the error bars are also labeled. By using the linear fitting of the experimental data, the Bi-induced bandgap reduction of about 56 meV/%Bi is obtained, which is smaller than the value of 88 meV/%Bi for GaAsBi [1] close to 55 meV/%Bi for InAsBi [15], but larger than 23 meV/%Bi for InSbBi [17]. Figure 2 Square of absorption coefficient Selleckchem Tideglusib of InPBi samples. Square of absorption coefficient of InPBi samples with various Bi compositions as a function of photon energy at room temperature. Figure 3 Bandgap energy of InPBi measured from absorption spectra as a function of Bi composition. The error bars of the experimental data are labeled. The solid line is the fitting line of the experimental data. Figure 4 shows the PL
spectra of InPBi films with Bi composition x Bi from 0.6% to 2.4% at RT. Strong and broad PL peaks are observed for the samples, except for the sample with the highest Bi composition. The PL peak energy BTK animal study first shifts from 0.9 eV (1.4 μm) to 0.65 eV (1.9 μm), when x Bi increases from 0.6% to 1.0%, and then turns back for the samples with a higher x Bi, but in all cases far from the bandgap energy. On the other hand, the InP reference sample only shows one PL peak at around 1.34 eV (0.93 μm) corresponding to the band-to-band transition. The InPBi sample with x Bi = 0.6% shows a very broad PL envelope from about 1.2 eV (1 μm) to 0.5 eV (2.5 μm), with a peak wavelength at around 0.9 eV (1.4 μm). The sample with 6-phosphogluconolactonase x Bi = 1.0% reveals the longest PL wavelength (peak at about 1.9 μm) and the strongest intensity. As the Bi composition further increases, the PL wavelength starts to blueshift and the PL FHPI intensity decreases. For the sample with 1.4% Bi, the PL peak is blueshifted to around 0.73 eV (1.7 μm) and the PL intensity is weakened to about 1/40 of the sample with the strongest PL intensity.
No PL signal was detected for the sample with 2.4% Bi. The clear RT PL signals far from the InPBi bandgap are unexpected. The Bi incorporation into GaAs was found to induce shallow localized states associated with Bi clusters above the top of the GaAs valence band due to the valence band anticrossing interaction, thus causing the red shift of PL [1, 18]. In addition, the Bi in InP with a doping level was found to act as isoelectronic impurities and revealed rich spectroscopic information near the bandgap of InP (1.3 to 1.4 eV) at low temperatures [10, 11]. However, the effects of cluster localization and isoelectronic impurities both introduce the PL peak red shift near the InP bandgap energy, in contrast to the PL signals observed from the middle of the bandgap. Figure 4 PL spectra of InPBi films with various Bi compositions at RT. The PL spectrum of InP reference sample is also shown.