# A High-Performance Thin-Film Sensor in 6G for Remote Sensing of the Sea Surface
## 3 Results and Discussion
The experimental setup is schematically shown in Figure 1a. First, all test benches were strictly grounded to prevent electrostatic generation, and the THz detector was placed in the center of the probe platform with two tungsten probes (with a 1 \(\upmu\)m tip) in contact with the metal electrodes of the device and connected to a digital source meter. The digital source meter (Keithley2400) applied a voltage range of 0-200 V and had a current test accuracy of 2 nA. A TeraSense IMPATT diode at 0.1 THz with an output power of 70 mW was employed as the THz emitter. The THz beam was not focused on the sample. A copper conical horn antenna was used for the coupling output. In addition, a THz power meter (ELVA-1 DPM R-1612) was first used to measure the THz power before starting the experiment, when the distance between the emitting end of the IMPATT diode and the power meter was equal to the distance where the sample was to be placed on the probe platform. The THz response of the device was obtained from the tested I-V curve. The response characteristics of three large-area Te films with different degrees of crystallization to THz waves were tested in the experiment. The noise characteristics are shown in Figure 4. For the Te films annealed at 100 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, and no annealing, the total noise (\(V_{n}\)) was \(1\times 10^{-7}\) V/Hz\({}^{1/2}\), \(1.12\times 10^{-7}\) V/Hz\({}^{1/2}\), \(1.32\times 10^{-7}\) V/Hz\({}^{1/2}\), respectively. The experimental results show that a higher degree of Te crystallization leads to lower noise. The increase in Vn with increasing bias is mainly caused by an increase in \(V_{b}\). In addition, Figure 4 shows the \(R_{A}\), \(NEP\), and \(D^{\star}\) of the device at different bias voltages when operating in the 6G experimental band, i.e., 0.1 THz, at room temperature (26 \({}^{\circ}\)C, 70% air humidity). For 100 \({}^{\circ}\)C annealing temperature, 200 \({}^{\circ}\)C annealing temperature, and no annealing temperature, the \(R_{A}\) of the Te films at a bias voltage of 20 V were 19.8 A/W, 18.2 A/W, and 13.5 A/W. The NEP are 2.8 pW\(\cdot\)Hz\({}^{-1/2}\), 3.1 pW\(\cdot\)Hz\({}^{-1/2}\), and 3.6 pW\(\cdot\)Hz\({}^{-1/2}\). The final detection rates \(D^{\star}\) were 1.85 \(\times\) 10\({}^{10}\) cm Hz\({}^{-1/2}\) W\({}^{-1}\), 1.79 \(\times\) 10\({}^{10}\) cm Hz\({}^{-1/2}\) W\({}^{-1}\), and 1.53 \(\times\) 10\({}^{10}\) cm Hz\({}^{-1/2}\) W\({}^{-1}\), respectively. We tested the THz detection performance of Te films under different annealing conditions and found that the better the crystallization effect of the Te films, the higher the detection performance, which was reflected in the parameters, namely, the large photo-sponsivity \(R_{A}\), small \(NEP\), large \(D^{\star}\), and small overall noise. Thin films with a higher degree of crystallization exhibited higher carrier migration efficiency and a more beneficial energy band structure of the Weyl semiconductor for THz detection, i.e., the unique optical selection rules followed by Te during the leap within a single Weyl cone and between different Weyl cones. The crystalline Weyl semiconductor Te exhibited ultra-high mobility, a strain- and thickness-tunable band gap, and a two-dimensional layered structure with outstanding air stability. These results eventually led to a high light-current response from Te. So, the detection efficiency of the crystallized Te film was further enhanced, and considering its excellent stability and non-hygroscopic properties, it can be used in high-humidity environments, making it an ideal detector for ocean remote sensing. The response rates of devices with Te thin films annealed at 100 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, and no annealing of 78 ms, 93 ms, and 104 ms were obtained due to the limitation of the test sampling rate (as shown in Figure 5). The results of the response rate correspond to the detection performance and Raman test results. In addition, the test can be more accurate if it is performed at a high current sampling time.