Lanzhong Hao

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 ...

The interface effect of the effective electrical conductivity of carbon nanotube composites

A model of the effective electrical conductivity for carbon nanotube (CNT) composites is presented by incorporating the interface effect with an average field theory. The dependence of the effective electrical conductivity on CNT length, diameter, concentration, and interface properties has been taken care of simultaneously in our treatment so that the model can describe well the interface effect of CNT composites. Predictions from the model are in good agreement with the experimental values of the effective electrical conductivity of CNT composites which the classical models have not been able to explain.

Ammonia sensitivity of amorphous carbon film/silicon heterojunctions

The amorphous carbon film/n-Si (a-C∕Si) junctions have been fabricated by magnetron sputtering. The results show that these junctions have good rectifying properties and high ammonia (NH3) gas sensitivity. For a given reverse bias voltage, the resistance of the junction can increase by 100 times rapidly when exposed to NH3 gas. This phenomenon may be attributed to the change of the space charge width of the junction, which is caused by the adsorption of NH3 gas molecules. This study shows that these a-C∕Si junctions have potential application as NH3 gas detect sensors.

Influence of chirality on the interfacial bonding characteristics of carbon nanotube polymer composites

The influence of chirality on the interfacial bonding characteristics of single-walled nanotubes (SWNTs) reinforced polymer composites was investigated using molecular mechanics and molecular dynamics simulations. The simulations indicate that the interfacial bonding and shear stress between the SWNT and the poly(methyl methacrylate) depends on the chirality. For SWNTs with similar molecular weights, diameters, and lengths, nanotubes with larger chiral angles achieve higher bonding energy and the armchair nanotube may be the best nanotube type for reinforcement. The general conclusions derived from this work may be of importance in devising advanced nanotube reinforced composites.

Effect of gas pressure on current-voltage characteristics of amorphous carbon film/silicon heterojunction

Amorphous carbon film/n-Si (a-C∕Si) junctions have been fabricated by direct current magnetron sputtering and their current-voltage (I-V) characteristics have been investigated. The results show that the gas pressure has a large effect on the reverse bias I-V characteristics of the junctions. For example, the reverse current can increase by 3300% when the gas pressure decreases from 100000to100Pa. The effect of gas pressure may be attributed to the physisorption process of gas molecules which increases the space charge width and changes the surface states of the junction.

Abnormal I‐V characteristics and metal-insulator transition of Fe-doped amorphous carbon∕silicon p‐n junction

Simple p‐C∕n‐Si junctions have been fabricated by magnetron sputtering at room temperature and their current-voltage (I‐V) characteristics have been investigated. The p‐n junctions show good rectifying properties in a large voltage scope and interesting I‐V characteristics. The most interesting phenomenon observed in these p‐n junctions is that the temperature dependence of some junction resistance shows a metal-insulator transition whose transition temperature is hugely modulated from 162to236K by a bias voltage increasing from 20to40V. This work shows that amorphous carbon films combined with other semiconductor materials can result in some interesting properties that may have potential applications.

Forward tunneling effect and metal-insulator transition in the BaTiO3 film/Si n-n heterojunction

A n-n heterojunction composed of BaTiO3 film and silicon substrate was fabricated, and it shows good rectifying properties in the temperature range of 80–300K. The forward tunneling effect in the junction at low temperatures ( 12V). The temperature dependence of the junction resistance under a high forward field exhibits an electrical field controlled metal-insulator transition. The results were explained by using the band structure of the junction.

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.