Fig. 1. (a) AFM image of the high-quality Bi2Se3 film. It is grown on the p-type Si (111) substrate, which is highly doped by boron, by using the MBE under a base vacuum ∼1.0 × 10−10  Torr. (b) XRD pattern of Bi2Se3 film after subtracting the signal from the p-type Si (111) substrate. (c) and (d) RHEED patterns of the Bi2Se3 film grown on the Si (111) substrate along the [112¯] (Γ–M) and [11¯0] (Γ–K) directions, respectively. (e) Room temperature Raman spectrum of eight QL Bi2Se3 thin film.

Fig. 2. (a) TR spectrum acquired with 1.78–3.04 eV probe energy. (b) The reflection change for probe energy levels at three white dashed lines of (a).

Fig. 3. (a) TR trace acquired at 2.32 eV, which is divided into four parts. (b) The energy spectrum plotted as a function of amplitude. (c) The schematic diagram of the pump and probe processes.

Fig. 4. (a) TR spectrum of eight QL Bi2Se3 thin films grown on the STO substrate. (b) TR spectrum of eight QL Bi2Se3 thin films grown on the Al2O3 substrate.

Fig. 5. (a) Amplitude changes linearly with the increasing pump fluence. (b) The TR traces of samples grown on Al2O3 (black line) and STO (blue line) substrates extracted at the probe energy of 2.32 eV.