# A High-Performance Thin-Film Sensor in 6G for Remote Sensing of the Sea Surface
## 3 Results and Discussion  
The main parameters of THz detectors are total noise (\(V_{n}\)), photoresponsivity (\(R_{A}\)), noise equivalent power (\(NEP\)), detection rate (\(D^{*}\)), and response time. Detector total noise (\(V_{n}\)) is inherent to the detector, and it is impossible to eliminate it artificially. Noise includes external noise (man-made noise and natural noise) and internal noise (scattered particle noise, thermal noise, etc.). The device that generates an alteration in the current or voltage as a result of light reception is referred to as a signal detector. Noise, on the other hand, is an irregular fluctuation in the output that occurs alongside the signal. Typically, noise is regarded as random, and its average over time is zero. Consequently, the magnitude of noise cannot be determined via time averaging. As the total power of noise is the sum of different noise powers, the root mean square noise voltage serves as a suitable measure for assessing the magnitude of noise [38]. \(V_{n}\) mainly includes the thermal Johnson-Nyquist noise (\(V_{t}\)) and the dark current noise (\(V_{b}\)) introduced by the addition of the bias voltage, which is defined as follows [38]:  
\[v_{n}=\left(v_{t}^{2}+v_{b}^{2}\right)^{1/2}=\left(4k_{B}Tr+2 qI_{d}r^{2}\right) ^{1/2} \tag{3}\]  
where \(k_{B}\) is the Boltzmann constant, \(T\) is the absolute detector temperature in Kelvin, \(r\) represents the resistance of the device in \(\Omega\), \(q\) is the fundamental charge, and \(I_{d}\) is the dark current of the device. The thermal Johnson-Nyquist noise is caused by the random thermal motion of carriers inside the material due to thermal stirring, independent of the added voltage, and the total noise \(V_{n}\) rises with an increase in voltage bias, which is caused by an increase in vb due to the change in voltage bias. Photoresponsivity (\(R_{A}\)) is the changing current of the device under illumination, defined as the photocurrent generated per unit of optical power, which can be expressed as follows [38]:  
\[R_{A}=\frac{I}{P} \tag{4}\]  
where \(P\) is the power of the THz source. Thus, the equation represents the effective detection response of the detector to THz waves, and the higher optical responsiveness of the device shows its higher photoelectric conversion efficiency. The noise equivalent power (\(NEP\)) is a metric that quantifies the sensitivity of a detector by measuring the minimum optical power it can detect. It is calculated by dividing the signal optical power by the square root of the bandwidth and the signal-to-noise ratio. A lower NEP indicates a higher ability to detect weak signals [38]:  
\[NEP=\frac{v_{n}}{R} \tag{5}\]The detection rate (\(D^{\star}\)) is a crucial parameter that measures the normalized signal-to-noise performance of a detector. It is directly linked to the equivalent noise power, meaning that a higher detection rate indicates a better detection performance of the device. \(D^{\star}\) serves as a parameter for evaluating the sensitivity of various detectors with different effective areas, allowing for a standardized assessment of their detection capabilities., defined as follows [38]:  
\[D^{\star}=\sqrt{S}/NEP \tag{6}\]  
where \(S\) is the detection effective area and the normalized detection rate \(D^{\star}\) is often used to compare the detection performance of the different detectors. The speed at which a detector responds is a crucial factor for its performance. This is particularly important for applications such as photoelectric detection, remote sensing, and fast imaging. The response time refers to the time it takes for the detector to generate a specific output in response to radiation. This response time is determined by the rise and fall times of the detector's output signal when a step signal light is inputted. In general, the rise time is the time it takes for the detector output pulse signal to increase from 10% to 90% of the leading edge, whereas the fall time is the time it takes for the signal to decrease from 90% to 10% of the trailing edge.