Zhipeng Wu

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.

Fabrication and electrical properties of LiNbO3/ZnO/n-Si heterojunction

Lithium niobate (LiNbO3 or LN) ferroelectric films were grown on n-type Si (100) substrates using ZnO as buffer layers by pulse laser deposition technique. The microstructures and electrical properties of the heterojunctions were studied. X-ray diffraction results showed that single (001) orientation for the LN films can be promoted on Si (100) substrates with the buffer effect of the ZnO layers. Due to the ferroelectric polarizations of the LN films, hysteretic characteristics were observed from the capacitance-voltage (C-V) curves of the LN/ZnO/n-Si heterojunctions. Obvious photoresponse characteristics were exhibited in the fabricated heterojunction. High performance of the photoresponse of the heterojunction was shown, such as a large ON/OFF ratio, short photoresponse time, steady ON or OFF states, and well reversible. These characteristics make it possible for the heterojunctions to develop multifunctional applications, such as memory devices, eletro-optic devices, and etc. The studied results show t...

Enhancing electrical properties of LiNbO3/AlGaN/GaN transistors by using ZnO buffers

LiNbO3 (LN) ferroelectric films were deposited on the ZnO buffered AlGaN/GaN templates by pulse laser deposition technique. The microstructures of the buffer layers and LN films were characterized by reflective high energy electron diffraction, atomic force microscope, and X-ray diffraction, respectively. With the help of Cu/Si3N4 double-layer masks, LN/ZnO/AlGaN/GaN transistors were fabricated and the electrical properties were studied. Normally off characteristics were exhibited for the fabricated transistors with LN gate layers. Due to the modifications of the 5-nm-thick ZnO layer to the interface, the electrical properties of the transistor were enhanced greatly. The maximum transconductance increased from 27 to 46 mS/mm, and the maximum drain current increased from 97 to 204 mA/mm. The operation mechanisms of the devices were proposed by the numerical calculations of the electronic band structure and charge distribution.

Enhanced Ferroelectric Properties of Pb(Hf0.3Ti0.7)O3 Thin Films by SrRuO3 Bottom Electrode

Lead Hafnate-Titanate, Pb(Hf0.3Ti0.7)O3 (PHT), films were fabricated by PLD on Al2O3 (0001) substrates with Pt or SrRuO3 (SRO) bottom electrodes, respectively. There is a certain amount of pyrochlore phase in PHT films on Pt/Al2O3. In contrast, the PHT films on SRO/Al2O3 show pure pervoskite phase. Furthermore, the PHT thin films on SRO/Al2O3, show uniform gain size and significantly enhanced ferroelectric properties with larger remnant polarization (2 Pr = 59.1μC/cm2), better fatigue endurance and lower leakage current density (8.5 × 10−8A/cm2 at 150 kV/cm). With the enhanced properties, PHT ferroelectric film on SRO electrode could be a promising structure which can be applied in FeRAM.