Yunjie Liu

Electrical and photovoltaic characteristics of MoS2/Si p-n junctions

Bulk-like molybdenum disulfide (MoS2) thin films were deposited on the surface of p-type Si substrates using dc magnetron sputtering technique and MoS2/Si p-n junctions were formed. The vibrating modes of E12g and A1g were observed from the Raman spectrum of the MoS2 films. The current density versus voltage (J-V) characteristics of the junction were investigated. A typical J-V rectifying effect with a turn-on voltage of 0.2 V was shown. In different voltage range, the electrical transporting of the junction was dominated by diffusion current and recombination current, respectively. Under the light illumination of 15 mW cm−2, the p-n junction exhibited obvious photovoltaic characteristics with a short-circuit current density of 3.2 mA cm−2 and open-circuit voltage of 0.14 V. The fill factor and energy conversion efficiency were 42.4% and 1.3%, respectively. According to the determination of the Fermi-energy level (∼4.65 eV) and energy-band gap (∼1.45 eV) of the MoS2 films by capacitance-voltage curve and ...

Growth and humidity-dependent electrical properties of bulk-like MoS2 thin films on Si

Bulk-like molybdenum disulfide (MoS2) thin films were deposited on Si substrates using a dc magnetron sputtering technique and n-MoS2/p-Si junctions were fabricated at room temperature (RT) and 400 °C, respectively. The typical oscillating modes of E12g and A1g were shown in the Raman spectra of the as-grown MoS2 films. Atomic force microscopy illustrated that the surfaces of the films were composed of dense nanoscale grains and scanning electron microscopy revealed the existence of large quantities of pores in the surface. The current–voltage curves of the junctions showed obvious rectifying characteristics due to the energy-band bending near the interface of MoS2/Si. The fabricated junctions exhibited humidity-dependent electrical properties. Compared with the one with the MoS2 film deposited at RT, the junction fabricated at 400 °C showed much more obvious sensing properties to humid gas. In particular, the sensitivity of the device could be tuned by external electrical fields. In the forward voltage range, the currents increased significantly after the junction was exposed to humid conditions. The response increased with increasing voltage and reached a saturated value after V = 1.9 V. The sensing performance featured high sensitivity, fast response and recovery. The junction current in the reverse voltage range decreased under the humid condition. This was contrary to that in the forward voltage range. We also studied the dependence of the sensing response on humidity levels. An almost linear correlation was obtained in the measured range of humidity levels. The sensing mechanisms of the MoS2/Si heterojunction were proposed.

Self-powered photosensing characteristics of amorphous carbon/silicon heterostructures

Amorphous carbon (a-C) thin films are deposited on p-type silicon (Si) substrates using magnetron sputtering technique and the photodetector devices based on the a-C/Si heterostructures are fabricated. The photosensing characteristics of the devices are investigated. Under light irradiation, the fabricated a-C/Si device exhibits obvious photovoltaic characteristics. This enables its application as a self-powered photodetector operated at zero bias voltage. The obtained results show that the device is highly sensitive to broadband wavelength from the ultraviolet to near-infrared light, showing a high detectivity of ∼2.9 × 1013 cm Hz1/2 W−1, as well as a high responsitivity of ∼292.5 mA W−1, and a fast response speed of ∼8.3 μs. The mechanisms to the self-powered photosensing characteristics are clarified by the determination of the energy-band alignment near the interface of the a-C/Si heterostructures.

Highly Enhanced H 2 Sensing Performance of Few-Layer MoS 2 /SiO 2 /Si Heterojunctions by Surface Decoration of Pd Nanoparticles

A novel few-layer MoS2/SiO2/Si heterojunction is fabricated via DC magnetron sputtering technique, and Pd nanoparticles are further synthesized on the device surface. The results demonstrate that the fabricated sensor exhibits highly enhanced responses to H2 at room temperature due to the decoration of Pd nanoparticles. For example, the Pd-decorated MoS2/SiO2/Si heterojunction shows an excellent response of 9.2 × 103% to H2, which is much higher than the values for the Pd/SiO2/Si and MoS2/SiO2/Si heterojunctions. In addition, the H2 sensing properties of the fabricated heterojunction are dependent largely on the thickness of the Pd-nanoparticle layer and there is an optimized Pd thickness for the device to achieve the best sensing characteristics. Based on the microstructure characterization and electrical measurements, the sensing mechanisms of the Pd-decorated MoS2/SiO2/Si heterojunction are proposed. These results indicate that the Pd decoration of few-layer MoS2/SiO2/Si heterojunctions presents an effective strategy for the scalable fabrication of high-performance H2 sensors.

Enhanced photovoltaic characteristics of MoS2/Si hybrid solar cells by metal Pd chemical doping

MoS2/Si hybrid solar cells are fabricated and the device performances are improved via metal Pd chemical doping. Due to the incorporation of the Pd atoms in the MoS2 films, the photovoltaic characteristics of the solar cell are enhanced significantly and a 375% enhancement of the power conversion efficiency can be obtained.

Density functional theory study of hydrogenation of S to H2S on Pt–Pd alloy surfaces

In this work, the adsorption of S-containing species (S, HS, and H2S) and the hydrogenation of S on the Pt–Pd alloy were investigated by using the periodic density functional theory (DFT). The energy minimum of the adsorbed S, HS, and H2S were identified to bind preferentially on the fcc, bridge and top sites, respectively. Compared to single metal surfaces, the adsorption energies of adsorbates were calculated to be larger on the Pt–Pd alloy surfaces and adsorbed preferably on the sites with a majority of Pt atoms. The reaction pathways and energy profiles for the conversion of adsorbed S and H into gas phase H2S were determined. The results showed that both the S + H and HS + H reactions on Pt–Pd alloy surfaces were endothermic. The energy for the overall reaction on Pt–Pd alloy surfaces decreased significantly by 0.30–0.55 eV compared to pure Pt(111) surface. In addition, the energy barrier on Pt–1Pd(111) (one Pt atom was replaced by Pd atom on Pt(111) surface) was lower than that on other studied alloy surfaces. The above characteristics revealed that the hydrogenation of S to H2S was easier on Pt–1Pd(111) surface than on the other alloy surfaces. The partial density of states was utilized to illustrate the interaction mechanisms between S-containing species and surface atoms.

Correction: Enhanced photovoltaic characteristics of MoS2/Si hybrid solar cells by metal Pd chemical doping

Correction for ‘Enhanced photovoltaic characteristics of MoS2/Si hybrid solar cells by metal Pd chemical doping’ by L. Z. Hao et al., RSC Adv., 2016, 6, 1346–1350.