# A Near-Ultraviolet Photodetector Based on the TaC: Cu/4 H Silicon Carbide Heterostructure
## 3 Results and Discussions
### Photoreponse Characteristics  
The performance of the photoresponse device was evaluated through its current-voltage (I-V) characteristics. Figure 6 illustrates the variation in dark current with applied voltage. In the reverse bias region, the dark current increases exponentially as the voltage rises from \(-1.75\) V to 0 V. When the bias voltage shifts to the positive range (forward bias), the current shows a rapid exponential growth from 0 V to 1.75 V.  
Figure 7a shows the relationship between the total current and applied bias voltage at different light intensities. It reveals that the total photocurrent increases linearly with light intensity under reverse bias. Furthermore, the relationship between photocurrent and light power at a reverse voltage is depicted in Figure 7b. The photocurrent initially grows linearly with increasing light power but reaches a saturation point beyond 400 \(\mu\)W, after which no significant increase is observed. Figure 5: (**a**) The schematic structure of the TaC: C/4H SiC hybrid structure. (**b**) The FDTD simulation region used to simulate the optical absorption and transmittance of the TaC: Cu alloy on SiC. (**c.d**) The simulated optical absorption and transmission as a function of the wavelength for the TaC: Cu alloy on SiC, respectively. Figure 6: The dark current of the TaC: Cu/4H SiC heterostructure. The responsivity of the fabricated device was calculated using the following equation [60]:  
\[R=\frac{|I_{total}-I_{dark}|}{P_{optical}} \tag{1}\]  
where \(I_{light}\) denotes the illuminated current, \(I_{dark}\) represents the dark current, and \(P_{optical}\) stands for the incident optical power. Figure 8a illustrates the relationship between responsivity and incident optical power. The responsivity exhibits significant variation with changes in incident power. Initially, it increases with rising incident power and stabilizes at approximately 380 uW. Beyond this threshold, the responsivity decreases sharply as the incident power continues to rise. This behavior is attributed to the saturation of the photocurrent at higher power levels, which reduces the responsivity. The measured responsivity values at applied voltages of 0.4 V, 1 V, and 1.75 V were 0.195, 0.544, and 1.66 A/W, respectively. Figure 8b presents the normalized responsivity of the photodetector across different wavelengths. The normalized responsivity was measured using four LED sources and relatively normalized to the responsivity at 405 nm. The graph includes three curves corresponding to different applied voltages: the black line for 0.4 V, the red line for 1 V, and the blue line for 1.75 V. The responsivity reaches its peak value of 1 at 405 nm and gradually decreases to 0.915 at 650 nm. Another critical parameter for evaluating photodetector performance is detectivity (D*), which was determined using the following equation [61]:  
\[D^{*}=R\sqrt{\frac{A_{e}}{2 qI_{dark}}} \tag{2}\]  
Figure 8: (**a**) Photresponsivity as a function of input power. (**b**) The normalized responsivity plotted against wavelength. Figure 7: (**a**) The total illuminated current and (**b**) the photocurrent variation with power. where \(R\) refers to the responsivity, \(A_{e}\) represents the area under illumination, \(q\) is the electron charge, and \(I_{dark}\) denotes the dark current. By applying these parameters to the above equation, the highest obtained detectivity was \(2.69\times 10^{8}\) [PERSON] at 1.75 V, and this dropped with the increase in the incident power. To evaluate the time response of the device, a Q-switched laser source with a peak power of 1500 W, a pulse duration of 10 ns, and a repetition rate of 1 kHz was employed. An optical attenuator was utilized to decrease the average beam power to 1 mW.