Fourth, significant injection of photo-excited carriers from GaAs to TI. The evidence for injection of photo-generated carriers from GaAs to TI is directly provided by a substantial increase of PTE current when . (For the measurements of , an imbalanced geometry was employed to provide a non-vanishing that can directly monitor injection of hot carriers from GaAs and its relative contribution as compared with the PTE current component arising from the photoexcitation of the Bi2Te3 film alone.) Carrier injection gives rise to an increase of ～40% in as compared with that observed with , as shown in Fig. 3a. As the contribution to from photo-generation of hot electrons within Bi2Te3 itself should be smoothly varying with near , which is well above the Bi2Te3 bandgap energy , the observed abrupt increase of when must arise from a different source of hot electrons other than Bi2Te3. The possibility that the observed 40% increase in is merely due to reabsorption of the PL emission Led SMD Bulbs from the GaAs substrate by the TI film can be safely excluded here as the DAP intensity from the substrate was experimentally measured to be at least six orders of magnitude weaker than the laser light. This leaves the injection of photo-generated electrons from GaAs to TI, driven by a large bandgap mismatch between them (), as the only plausible explanation for the observed sharp increase of in Bi2Te3.

Figure 3: Carrier and spin injection from GaAs to TI.
Figure 3
(a) PTE current in the S1 sample, generated intentionally under an imbalanced excitation condition. The current rise observed when the photon energy is tuned above the bandgap energy of GaAs (), with the onset around 1.52?eV, is a result of carrier injection from the GaAs substrate to TI. (b) Helicity-dependent photocurrent as a function of excitation photon energy at the normal incidence measured at 5?K from both S1 and S2 samples. The error bars were estimated from the statistics of 300 data points collected in steady-state measurements.
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To further confirm <a href="">carrier </a>injection from GaAs to Bi2Te3, we have conducted time-resolved PL (TR-PL) experiments to examine carrier/exciton lifetime in GaAs that could be affected by the injection process. As band-edge excitons in GaAs are formed by binding photo-generated electron–hole pairs and free excitons additionally have a chance to diffuse to the GaAs/TI interface, thereby contributing to carrier injection, the exciton emission X was closely monitored in our TR-PL studies. It is clearly seen from the results shown in Fig. 2c that the exciton lifetime of the GaAs substrate is significantly shorter in the Bi2Te3/GaAs structure (for example, Sample S2) than that in the reference sample of the bare GaAs substrate (for example, Sample Sub.2). Besides the radiative and non-radiative recombination processes common to GaAs in both the Bi2Te3/GaAs structure and the bare GaAs substrate, a major difference between the two structures that can affect the GaAs exciton lifetime is the presence of an additional loss channel for carriers/excitons in GaAs due to their injection to Bi2Te3 in the former structure. This finding thus provides further evidence for efficient carrier/exciton injection that tends to deplete the carriers/excitons in GaAs at and near the TI/GaAs interface.