A High‐Photocurrent and Fast‐Response Polarity‐Controlled ZnO‐Based UV Photodetector Grown by a Sol–Gel Process

Abstract

Oxygen‐polar (O‐polar) and nonpolar ZnO‐based UV photodetectors (PDs) are fabricated using a sol–gel (SG) method on polarity‐controlled ZnO seed layers grown by atomic layer deposition (ALD). O‐polar c‐plane and nonpolar a‐plane ZnO films grown using the SG process are obtained using ALD‐grown ZnO seed layers on c‐plane and r‐plane sapphire substrates, respectively. In addition, the photoluminescence intensity of the O‐polar c‐plane ZnO film is higher than that of the nonpolar a‐plane ZnO film owing to the introduction of the ZnO seed layer. Therefore, the resulting photocurrent of the O‐polar c‐plane ZnO PD is higher than that of the nonpolar a‐plane ZnO PD. Furthermore, regardless of the crystal polarity, the carrier concentration and the mobility of the ZnO film deposited using the SG method significantly increase because of the ZnO seed layer. In particular, the carrier concentration of the nonpolar a‐plane ZnO film is 2.5 times higher than that of the O‐polar c‐plane ZnO film. Therefore, the time‐dependent photoresponsivity of the nonpolar a‐plane ZnO PD is faster than that of the O‐polar c‐plane ZnO PD. These results indicate that the ZnO seed layers can effectively control the crystal polarity of ZnO films grown using the SG method.

High‐Efficiency ZnO‐Based Ultraviolet Photodetector with Integrated Single‐Walled Carbon Nanotube Thin‐Film Heater

“…It is believed that the decrease in photocurrent above 80 °C is due to thermal oxidation becoming dominant above this temperature. [ 18 ] The thermal oxidation process is thought to accelerate the desorption of surface oxygen, which negatively affects the photocurrent reduction of ZnO PD. Figure 5b illustrates the relationship between the saturation time for the maximum photocurrent of the ZnO PD and the reciprocal temperature of the SWCNT film heater.…”

“…Using Arrhenius equation, the activation energy for the photocurrent saturation time of ZnO PDs is calculated to be 203 meV, which is lower than values obtained from conventional temperaturedependent measurement system. [18,46] It implies that the hybrid ZnO PDs with SWCNT film heater are more efficient in adding thermal energy to improve photocurrent, compared to conventional separated thermal heating system. Figure 5c shows the rise and recovery times of the hybrid ZnO PDs as a function of the operating temperature of the SWCNT film heater, which is controlled by applying a voltage for 0-40 V. The photoresponse rise time is defined as the time required to increase the photocurrent from 10% to 90% of the peak intensity, while the photo-recovery time is achieved by measuring the time required to decrease the photocurrent from 90% to 10% of its peak value.…”

“…[ 17 ] However, one of the main limitations of using sol–gel method is that it often results in lower crystallinity compared to other vacuum processes, leading to lower photo reaction and slower response times. [ 18 ]…”

“…[17] However, one of the main limitations of using sol-gel method is that it often results in lower crystallinity compared to other vacuum processes, leading to lower photo reaction and slower response times. [18] Overcoming challenges in the practical application of ZnObased PDs produced using the sol-gel method is still issues. The photoresponse of ZnO-based PDs can occur through both photoelectric and photoconductive effects, [19] and the resistance change in the ZnO thin film is caused by the adsorption and desorption of oxygen molecules on the surface, leading to a change in photocurrent.…”

High‐Performance Self‐Assembled ZnO Nanowrinkle Network Structured Photodetectors

“…Compared to the results of other research groups shown in Table 1, it is found that the ZnO PDs prebaked at 150 °C had relatively good response times. [35][36][37][38][39] It is believed that this is because the adsorption and desorption reactions of oxygen on the ZnO surface occur most rapidly in PDs with the largest NWNs structure, leading to the fastest response times. [40,41] At 150 °C, the PDs exhibit the largest and most well-defined NWNs structure, which enhances the light absorption and extraction efficiency and leads to the fastest response times.…”