Ultra-high Mobility Of P-type CdS Nanowires:Surface Charge Transfer Doping And Photovoltaic Devices

Low-dimensional semiconductor nanostructures have attracted a wide range ofresearch interests due to their excellent electrical and optical properties. Cadmiumsulfide （CdS）, as an important II–VI semiconductor with a wide direct band-gap of2.42eV at room temperature, is an important building block for optoelectronicdevices. Undoubtedly, doping is the premise of semiconductor materials fordevicesapplications. Hence, n-type doped CdS has been widely researched andsuccessfully prepared by researchers. However, p-type doping of CdS is stillunrealized because of the strong self-compensation effect of CdS. Therefore, thestudy of the p-type doping of CdS need to be expanded urgently.In this article, we realized the p-type doping of CdS nanowires via surfacecharge transfer doping by coating MoO₃thin film. Meanwhile, p-type CdSnanowires based homojunctions and heterojunctions photovoltaic devices weresuccessfully constructed by employing the mirco-nano manufacturing technologies,and their electrical and optical proteries were studied. The specific achievementsare as follows:1. High quality p-type CdS nanowires were successfully prepared via surfacecharge transfer doping by coating MoO₃thin film onto the surface of undoped CdSnanowires. The electrical test of the single CdS nanowire based bottom gatefield-effect transistor devices demonstratesthat the conduction type of CdSnanowires is transferred from weak n-type to p-type after coating MoO₃thin film.The resistance decreases from3.3×10¹¹ to4.7×10³with a decreasingamplitude up to7orders of magnitude. More important, the hole mobility is up to2035cm2V^-1s^-1. By other tests, the as prepared p-type CdS nanowires via MoO₃coating are verified to be repeatable and stabilized.2. We fabricated the single CdS nanowire based homojunctions photovoltaicdevices. The electrical test proved that the conduction type of n-type CdS: Gananowires could also be transferred into p-type by coating of MoO₃thin film.Based on the above results, the single CdS nanowire based homojunctions wereconstructed， demonstrating pronounced recticying behavior with rectification ratioof1.6×102from2V to+2V. The turn-on voltage and the diode ideality factor ofthe homojunction were estimated to be1V and2.8, respectively. Meanwhile, obvious photovoltaic properties were observed for the homojunction devices. Underwhile light illumination (1.5mW·cm^-2), the device demonstrated an open circuitphotovoltage （VOC） of0.10V, a short circuit current density （JSC） of0.72mA·cm2,and a fill factor （FF） of35.23%, yield a power conversion efficiency （η） of1.65%.3. We fabricated p-CdS nanowire/n-Si heterojunction device, which displaysobvious rectifying characteristics with rectification ratio of2.3×10²from1.5Vto+1.5V. The turn-on voltage and the diode ideality factor were calculated to be0.7V and2.4, respectively. What is more, the p-CdS nanowire/n-Si heterojunctiondevice also shown excellent photovoltaic properties. Under while light illumination(1.5mW·cm^-2), an VOCof0.15V, JSCof0.52mA·cm²and FF of19.2%wereobtained,yield a η of0.99%.