Surface/Interface Defect Engineering on Charge Carrier Transport toward Broadband (UV-NIR) Photoresponse in the Heterostructure Array of p-Si NWs/ZnO Photodetector

The surface/interface properties, especially interfacial states, have a key impact on overall carrier generation, recombination/transport, and/or collection proficiency for heterostructurebased photodetectors. This study demonstrates the significant enhancement of ultraviolet-near infrared (UV-NIR) (300-1100 nm) broadband photodetection in the heterostructure array of p-Si NWs/ZnO photodetectors with engineering of surface/interface charge carrier transportation under different processing conditions. In the case of a pulsed laser deposition (PLD)-grown photodetector, coupling of the subsidiary value of the defect state with the interfacial layer (Si-O-Zn) at the p-n junction reduces the charge carrier recombination, resulting in a large enhancement of transient photocurrent in the visible (Vis)-NIR region. However, in the case of a chemical solution deposition (CSD)-grown photodetector, plenty of oxygen vacancies (Vos) become the trap-assisted recombination centers by capturing of photoinduced carriers. The average value of responsivity (R) at 1 V bias for the PLD-grown detector is -5.5 A/W in the Vis-NIR (500-1100 nm) region, whereas in the UV region (<= 375 nm), the value of R reached -8 A/ W. The value of R in the PLD-grown detector is enhanced -102 folds in the UV region and -20 folds in the Vis-NIR region comparison with the CSD-grown detector. Further, carrier generation, trapping, and transport/recombination processes in the surface/interface are well illustrated to explain the dynamics of the charge carrier contributing to the photoresponse behavior in the UV-NIR broadband region

Piezoelectric Nanogenerators based on Lead Zirconate Titanate nanostructures: an insight into the effect of potential barrier and morphology on the output power generation

The high internal resistance of the perovskite materials used in Nanogenerators (NGs) lowers the power generation. It severely restricts their application for mechanical energy harvesting from the ambient source. In this work, we demonstrate a flexible Piezoelectric NG (PENG) with an improved device structure. Hydrothermally grown one-dimensional Lead Zirconate Titanate (Pb(ZrTi)O-3) of different morphologies are used as the generating material. The morphology of the PZT nanostructures, engineered from nanoparticles to needle-shaped nanowires to increase the surface to volume ratio, provides effective mechanical contact with the electrode. The reduction of the internal resistance of the PENG has been achieved by two ways: (i) fabrication of interdigitated electrodes (IDE) to increase the interfacial polarization and (ii) lowering of Schottky barrier height (SBH) at the junction of the PZT nanostructure and the metal electrode by varying the electrode materials of different work functions. We find that lowering of the SBH at the interface contributes to an increased piezo voltage generation. The flexible nano needles-based PENG can deliver output voltage 9.5 V and power density 615 mu W cm(-2) on application low mechanical pressure (similar to 1 kPa) by tapping motion. The internal resistance of the device is similar to 0.65 M omega. It can charge a 35 mu F super-capacitor up to 5 V within 20 s. This study provides a systematic pathway to solve the bottlenecks in the piezoelectric nanogenerators due to the high internal resistance

Enhanced piezoelectric response in BTO NWs-PVDF composite through tuning of polar phase content

We have fabricated a flexible, environment friendly piezoelectric nanogenerator (PENG) based on the ferroelectric Polyvinylidene fluoride (PVDF) composite incorporated with Barium titanate (BaTiO3) nanowires (NWs) of piezoelectric coefficient d (33) = 308 pm V-1. The single-layered PENG can deliver output power density of 10 mu W cm(-2) and an output voltage of 2 V with a nominal mechanical load of 1 kPa. BaTiO3 (BTO) NWs of different concentrations were incorporated into PVDF to tune the polar phase content, internal resistance, and optimize the output power. We show that there exists a critical value of BTO NWs loading of 15 wt%, beyond which the piezoelectric energy harvesting characteristics of the PVDF nanocomposites decrease. The oxygen vacancies present in the BTO NWs surface attract the fluorine ions of PVDF chain and favour the formation of beta phase. The enhanced value of dielectric constant and dielectric loss of BTO-PVDF samples in the low frequency region suggest strong interfacial polarization in the composite system. The fabricated PENG can charge a super-capacitor up to 4 V within 35 s. The origin of the high power output from the BTO (15 wt%)-PVDF composite is attributed to the combined effect of enhanced polar phase content, strong interfacial polarization, and reduced internal resistance. This study provides an effective pathway in enhancing the performance of BTO-PVDF based piezoelectric energy harvesters

Restoration of perovskite phase in the top layer of thin BTO film by plasma treatment and annealing

We report a simple method to restore the perovskite phase in the top surface/sub-surface region of a thin film (similar to 100 nm) of barium titanate (BTO) fabricated by pulsed laser deposition on a platinized silicon surface and thus enhance its dielectric and ferroelectric properties. Phase evolution, surface morphology with local chemical composition of as-grown BTO films have been studied as a function of laser fluence. Investigations using x-ray diffraction, grazing-angle incidence x-ray diffraction and depth resolved x-ray photoelectron spectroscopy show that even after achieving a good phase formation there can be a presence of non-perovskite TiO2 phase at the surface and subsurface in such films that degrades its dielectric and ferroelectric response. The restoration of the degraded top layer was done by a combination of low energy Ar plasma treatment followed by an annealing process that enhances Ba content