Jiadan Lin

Black Phosphorus Quantum Dots

As a unique two-dimensional nanomaterial, layered black phosphorus (BP) nanosheets have shown promising applications in electronics. Although mechanical exfoliation was successfully used to prepare BP nanosheets, it is still a challenge to produce novel BP nanostructures in high yield. A facile top-down approach for preparation of black phosphorus quantum dots (BPQDs) in solution is presented. The obtained BPQDs have a lateral size of 4.9±1.6 nm and thickness of 1.9±0.9 nm (ca. 4±2 layers). As a proof-of-concept application, by using BPQDs mixed with polyvinylpyrrolidone as the active layer, a flexible memory device was successfully fabricated that exhibits a nonvolatile rewritable memory effect with a high ON/OFF current ratio and good stability.

Surface transfer doping induced effective modulation on ambipolar characteristics of few-layer black phosphorus

Black phosphorus, a fast emerging two-dimensional material, has been configured as field effect transistors, showing a hole-transport-dominated ambipolar characteristic. Here we report an effective modulation on ambipolar characteristics of few-layer black phosphorus transistors through in situ surface functionalization with caesium carbonate (Cs2CO3) and molybdenum trioxide (MoO3), respectively. Cs2CO3 is found to strongly electron dope black phosphorus. The electron mobility of black phosphorus is significantly enhanced to ~27 cm(2) V(-1) s(-1) after 10 nm Cs2CO3 modification, indicating a greatly improved electron-transport behaviour. In contrast, MoO3 decoration demonstrates a giant hole-doping effect. In situ photoelectron spectroscopy characterization reveals significant surface charge transfer occurring at the dopants/black phosphorus interfaces. Moreover, the surface-doped black phosphorus devices exhibit a largely enhanced photodetection behaviour. Our findings coupled with the tunable nature of the surface transfer doping scheme ensure black phosphorus as a promising candidate for further complementary logic electronics.

Plasmonic enhancement of photocurrent in MoS2 field-effect-transistor

The two-dimensional material, molybdenum disulfide (MoS2), has attracted considerable attention for numerous applications in optoelectronics. Here, we demonstrate a plasmonic enhancement of photocurrent in MoS2 field-effect-transistor decorated with gold nanoparticles, with significantly enhanced photocurrent peaked at the plasmon resonant wavelength around 540 nm. Our findings offer a possibility to realize wavelength selectable photodetection in MoS2 based phototransistors.

Improved Photoelectrical Properties of MoS2 Films after Laser Micromachining

Direct patterning of ultrathin MoS2 films with well-defined structures and controllable thickness is appealing since the properties of MoS2 sheets are sensitive to the number of layer and surface properties. In this work, we employed a facile, effective, and well-controlled technique to achieve micropatterning of MoS2 films with a focused laser beam. We demonstrated that a direct focused laser beam irradiation was able to achieve localized modification and thinning of as-synthesized MoS2 films. With a scanning laser beam, microdomains with well-defined structures and controllable thickness were created on the same film. We found that laser modification altered the photoelectrical property of the MoS2 films, and subsequently, photodetectors with improved performance have been fabricated and demonstrated using laser modified films.

Modulating electronic transport properties of MoS2 field effect transistor by surface overlayers

In situ bottom-gated molybdenum disulfide (MoS2) field effect transistors (FETs) device characterization and in situ ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy measurements were combined to investigate the effect of surface modification layers of C60 and molybdenum trioxide (MoO3) on the electronic properties of single layer MoS2. It is found that C60 decoration keeps MoS2 FET performance intact due to the very weak interfacial interactions, making C60 as an ideal capping layer for MoS2 devices. In contrast, decorating MoO3 on MoS2 induces significant charge transfer at the MoS2/MoO3 interface and largely depletes the electron charge carriers in MoS2 FET devices.

Inversion-Mode Self-Aligned

A high-performance In_0.53Ga_0.47As n-channel MOSFET integrated with a HfAlO gate dielectric and a TaN gate electrode was fabricated using a self-aligned process. After HCl cleaning and (NH₄)₂S treatment, the chemical vapor deposition HfAlO growth on In_0.53Ga_0.47As exhibits a high-quality interface. The fabricated nMOSFET with a HfAlO gate oxide thickness of 11.7 nm shows a gate leakage current density as low as 2.5 times 10^-7 A/cm² at V_g of 1 V. Excellent inversion capacitance was illustrated. Silicon implantation was self-aligned to the gate, and low-temperature activation for source and drain was achieved by rapid thermal annealing at 600degC for 1 min. The source and drain junction exhibited an excellent rectifying characteristic and high forward current. The result of an In_0.53Ga_0.47As nMOSFET shows well-performed I_d-V_d and I_d-V_g characteristics. The record high peak electron mobility of 1560 cm²/Vs has been achieved without any correction methods considering interface charge and parasitic resistance.

\hbox{In}_{0.53}\hbox{Ga}_{0.47}\hbox{As}

Plasma-based PH<inf>3</inf> passivation technique is extensively studied for the surface passivation of InGaAs substrate prior to high-k deposition. The comparative analysis reveals that the striking improvement is achieved when a stable covalent-bond P<inf>x</inf>N<inf>y</inf> layer forms at the interface during plasma PH<inf>3</inf>-passivation. We report that P<inf>x</inf>N<inf>y</inf> passivation layer improves thermal stability of high-k/InGaAs gate stack up to 750°C, which enables successful implementation of InGaAs MOSFETs by self-aligned gate-first process. By adopting P<inf>x</inf>N<inf>y</inf> passivation on InGaAs with MOCVD HfAlO and metal gate stack, we achieved subthreshold slope of 98mV/dec, G<inf>m</inf>=378mS/mm at V<inf>d</inf>=1V, and effective mobility of 2557cm²/Vs at E<inf>eff</inf>=0.24MV/cm.

N-Channel Metal-Oxide-Semiconductor Field-Effect Transistor With HfAlO Gate Dielectric and TaN Metal Gate

Interfacial reaction study using x-ray photoelectron spectroscopy was carried out for metal-organic chemical-vapor-deposited HfO2 and HfAlO gate dielectrics on p-In0.53Ga0.47As layer as compared to the cases of p-GaAs substrate. The results show that the alloying of GaAs with InAs (In0.53Ga0.47As) in the III-V channel layer and the alloying HfO2 with Al2O3 in the high-k dielectric can be an effective way to improve the interface quality due to their significant suppression effects on native oxides formation, especially arsenic oxide which causes Fermi level pinning on the high-k/III-V channel interface during the fabrication processes. Transmission electron microscopy result and the electrical characteristics of HfAlO∕p-In0.53Ga0.47As capacitors further validate the x-ray photoelectron spectroscopy observations.

Thermally robust phosphorous nitride interface passivation for InGaAs self-aligned gate-first n-MOSFET integrated with high-k dielectric

By using in situ field effect transistor characterization integrated with molecular beam epitaxy technique, we demonstrate the strong surface transfer p-type doping effect of single layer chemical vapor deposition (CVD) graphene, through the surface functionalization of molybdenum trioxide (MoO3) layer. After doping, both the hole and electron mobility of CVD graphene are nearly retained, resulting in significant enhancement of graphene conductivity. With coating of 10 nm MoO3, the conductivity of CVD graphene can be increased by about 7 times, showing promising application for graphene based electronics and transparent, conducting, and flexible electrodes.

Study on interfacial properties of InGaAs and GaAs integrated with chemical-vapor-deposited high-k gate dielectrics using x-ray photoelectron spectroscopy

Using in situ field effect transistor (FET) characterization combined with the molecular beam epitaxy technique, we demonstrate a significant depletion of electron charge carriers in single zinc oxide (ZnO) nanowire through the surface modification with molybdenum trioxide (MoO3) and 1, 4, 5, 8, 9, 11-hexaazatriphenylene hexacarbonitrile (HATCN) layers. The electron mobility of ZnO nanowire was found to sharply decrease after the surface modification with MoO3; in contrast, the electron mobility significantly increased after functionalization with HATCN layers. Such depletion of n-type conduction originates from the interfacial charge transfer, corroborated by in situ photoelectron spectroscopy studies. The air exposure effect on MoO(3-) and HATCN-coated ZnO nanowire devices was also investigated.