Fig. 1. (a) Schematic diagram of the device structure and measurement geometry. (b) Photocurrent as a function of the phase angle φ of the 10-QL (Bi0.9Sb0.1)2Te3 sample when the light spot is illuminated at oblique incidence of θ=30°. The solid line (black) is the fitting curve using Eq. (1). The dotted lines (purple and blue) and the dashed line (red) are the photocurrent induced by linearly and circularly polarized light, respectively. The dash-dotted line (green) indicates the polarization-independent current D.

Fig. 2. Dependence of the coefficients (a) C, (b) L1, and (c) L2 on the light incident angle (θ), which are extracted by fitting Eq. (1) to the polarization-dependent photocurrent of the 7-QL (Bi0.8Sb0.2)2Te3, 10-QL (Bi0.9Sb0.1)2Te3, and 20-QL (Bi0.9Sb0.1)2Te3 samples. The solid curve in (a) is the fitting curve by using JyCPGE+JyCPDE expressed by Eq. (2). The solid curves in (b) and (c) represent the fitting curve by using Eq. (7) and Eq. (8), respectively.

Fig. 3. Dependence of (a) CPGE and (b) LPGE currents of the 10- and 20-QL BST samples on the gate voltage, measured under θ=−30° at 77 K. (c) Dependence of the CPGE, LPGE, and LPDE currents on the gate voltage for the 7-QL BST sample measured at the incident angle θ=−30° at 77 K. (d) Dependence of the value of |C|/(|C|+|L1|+|L2|) on the gate voltage, which is the ratio of |C| to the sum of the absolute values of the polarization-dependent photocurrents (|C|+|L1|+|L2|).

Fig. 4. Dependence of the sheet resistance on the gate voltage for (a) the 10- and 20-QL (Bi0.9Sb0.1)2Te3 samples and (b) the 7-QL (Bi0.8Sb0.2)2Te3 sample at 77 K. The inset shows the schematic drawing of the position of Fermi level for the BST samples under different back gate voltages.

Fig. 5. Light incident angle dependence of the CPGE current under the front and back illuminations at room temperature for the 10- and 20-QL (Bi0.9Sb0.1)2Te3 samples. (a) Schematic illustrations of the CPGE measurement under the front and back illuminations. (b)–(d) Dependence of the CPGE current on the incident angle under the front and back illuminations for the 10-QL (Bi0.9Sb0.1)2Te3 sample, the 20-QL (Bi0.9Sb0.1)2Te3 sample, and the 7-QL (Bi0.8Sb0.2)2Te3 sample. The solid lines are the fitting curves using Eq. (2a).

Fig. 6. (a) Schematic diagram of the device structure and measurement geometry for the modulation of the CPGE by ionic liquid gating. (b) Schematic drawing of the band structure and the Fermi level position of the BST thin film under different ionic liquid voltages. (c) Comparison of the gating voltage dependence of the CPGE current under the back and top gatings for the 20-QL BST sample measured at θ=−30°.

Fig. 7. Dependence of the ratio Itotal/(IC+ID) of the measured and calibrated photocurrent on the phase angle φ under incident angle θ=±30°. The photocurrent is measured under the light illumination with a power of 110 mW at 77 K and back gate voltage of Vbg=−30  V. The intersections of the ratio Itotalmea/(ICcal+IDcal) and Itotalcal/(ICcal+IDcal) are marked out at φ=35°, 128°.

Fig. 8. Dependence of the fitting parameters C, D, L1, and L2 on the incident light power in the 7-QL (Bi0.8Sb0.2)2Te3 thin film under an incident angle (a) θ=−30° and (b) θ=30° at 77 K. (c) Dependence of the photoconductance on incident light power in the 7-QL (Bi0.8Sb0.2)2Te3 thin film.

Fig. 9. Dependence of the photocurrent, with the polarization-independent current D being substrated, on the angle of the quarter-wave plate α in the 7-QL BST sample. The photocurrent is measured under a light power of 110 mW and a back gate voltage of 260 V at 77 K.