## 3 Results
### Relationship between THz Time-Domain Waveform and Photocurrent
\[\frac{\frac{1}{k}}{\frac{1}{2.59\times 10^{5}}}=\frac{(n_{1}*\mu_{1}+n_{2}*\mu_{ 2})*E}{(n_{1}+n_{2})*\mu_{1}*E}, \tag{3}\]  
Assuming the \(\Gamma\) valley mobility is 6000 cm\({}^{2}\)/V \(\cdot\) s and 8000 cm\({}^{2}\)/V \(\cdot\) s, respectively, the electron mobility of its satellite valley (L valley) is 920 cm\({}^{2}\)/V \(\cdot\) s. The calculated photogenerated carrier transfer rate is shown in Table 1. \begin{table}
\begin{tabular}{c c c c} \hline
**Biased Electric Field (kV/cm)** & **Conversion Ratio (k)** & \(\Gamma\)**Valley (6000 cm\({}^{2}\)/V-s)** & \(\Gamma\)**Valley (8000 cm\({}^{2}\)/V-s)** \\ \hline
2.00 & \(2.59\times 10^{5}\) & \(\sim\)100\% & \(\sim\)100\% \\
3.33 & \(2.76\times 10^{5}\) & 92.73\% & 93.04\% \\
5.00 & \(3.60\times 10^{5}\) & 66.93\% & 68.30\% \\
6.67 & \(3.92\times 10^{5}\) & 60.04\% & 61.74\% \\
8.33 & \(4.35\times 10^{5}\) & 52.25\% & 54.28\% \\
10.00 & \(4.80\times 10^{5}\) & 45.46\% & 47.98\% \\
11.67 & \(5.28\times 10^{5}\) & 39.83\% & 42.43\% \\
13.33 & \(5.65\times 10^{5}\) & 36.06\% & 38.83\% \\ \hline \end{tabular}
\end{table} 
Table 1: The calculated of photogenerated carrier transfer rate. Figure 4: (**a**) THz time-domain waveform electric field integral curve. (**b**) Comparison between the photocurrent of THz integral and the measured by oscilloscope for a bias voltage of 100 V.  
Figure 5: The mean value and standard deviation of conversion ratio \(k\)  
The calculated results indicate that, with increasing electric field bias, the more photogenerated carriers in the \(\Gamma\) valley can receive extra enough energy from the bias electric field and finally transfer to the satellite valley, as shown in Figure 6.  
Figure 7 shows the carrier occupancy rate for the \(\Gamma\) valley when the \(\Gamma\) valley mobility is 8000 cm\({}^{2}\)/V \(\cdot\) s, fitted (using Origin 8.5) with the exponential function:  
\[\eta=1.0389*\exp\biggl{(}-\frac{E}{5.9953}\biggr{)}+0.277, \tag{4}\]  
Here, \(\eta\) is the carrier occupancy rate for the \(\Gamma\) valley, and \(E\) is the electric field bias. In the same way, when the \(\Gamma\) valley mobility is 6000 cm\({}^{2}\)/V \(\cdot\) s, the fitting curve can be described using Equation (5). \[\eta=1.0867*\exp\biggl{(}-\frac{E}{6.0065}\biggr{)}+0.244, \tag{5}\]  
In Equations (4) and (5), \(\eta\) is equal to 1. The initial electric field of inter-valley scattering of photogenerated carriers are 2.17 kV/cm and 2.18 kV/cm, respectively. In other words, when the  
Figure 6: The carrier occupancy rate for the \(\Gamma\) valley when the \(\Gamma\) valley mobility is 6000 cm\({}^{2}\)/V \(\cdot\) s and 8000 cm\({}^{2}\)/V \(\cdot\) s, respectively. Figure 7: Fitted curve to the carrier occupancy rate for the \(\Gamma\) valley when the \(\Gamma\) valley mobility is 8000 cm\({}^{2}\)/V \(\cdot\) s.  
electric field is less than 2.17 kV/cm and the \(\Gamma\) valley mobility is 8000 cm\({}^{2}\)/V \(\cdot\) s, all photogenerated carriers are located in the \(\Gamma\) valley. When the electric field is less than 2.18 kV/cm and the \(\Gamma\) valley mobility is 6000 cm\({}^{2}\)/V \(\cdot\) s, all photogenerated carriers are located in the \(\Gamma\) valley.