Zhi-Jun Qiu

A Comparative Study of Two Different Schemes to Dopant Segregation at NiSi/Si and PtSi/Si Interfaces for Schottky Barrier Height Lowering

An experimental study is presented to compare two different schemes used to incorporate a high concentration of dopants at the silicide/silicon interface for NiSi and PtSi, i.e., dopant segregation, with the purpose of lowering the Schottky barrier height (SBH) of the contact systems. Specifically, the interfacial dopant is introduced either through silicidation-induced dopant segregation (SIDS) or by silicide as diffusion source (SADS). For the latter, a postimplantation drive-in anneal is needed. For both silicide systems, the dopant segregation gives rise to a predominant effect, leading to an effective SBH that is independent of the original SBHs of PtSi and NiSi, which differs by 0.2 eV. Scheme SIDS is relatively simple in processing, but the silicidation process is dopant-dependent, leading to local variations of silicide formation. Scheme SADS addresses the adverse effect of dopant on silicidation by separating silicidation from dopant incorporation.

Schottky-Barrier Height Tuning by Means of Ion Implantation Into Preformed Silicide Films Followed by Drive-In Anneal

An experimental study on Schottky-barrier height (SBH) tuning using ion implantation followed by drive-in anneal of As, B, In, and P in preformed NiSi and PtSi films is presented. Measured on B-implanted NiSi and PtSi Schottky diodes, the effective SBH on n-type Si is altered to ~1.0 eV. For As- and P-implanted diodes, the SBH on p-type Si can be tuned to around 0.9 eV. The process window for the most pronounced SBH modification is dopant dependent.

SMALL-Hysteresis Thin-Film Transistors Achieved by Facile Dip-Coating of Nanotube/Polymer Composite

Small-hysteresis, high-performance thin-film transistors (TFTs) are readily realized simply by dip-coating of a solution-processable composite. The composite consists of single-walled carbon nanotubes (SWCNTs) embedded in semiconducting polymer used as the channel material. The resultant TFTs simultaneously exhibit large on/off current ratio, high on-current level, high mobility in the range 10-20 cm(2)V(-1)s(-1), and good uniformity and scalability.

Photothermoelectric and photovoltaic effects both present in MoS2

As a finite-energy-bandgap alternative to graphene, semiconducting molybdenum disulfide (MoS2) has recently attracted extensive interest for energy and sensor applications. In particular for broad-spectral photodetectors, multilayer MoS2 is more appealing than its monolayer counterpart. However, little is understood regarding the physics underlying the photoresponse of multilayer MoS2. Here, we employ scanning photocurrent microscopy to identify the nature of photocurrent generated in multilayer MoS2 transistors. The generation and transport of photocurrent in multilayer MoS2 are found to differ from those in other low-dimensional materials that only contribute with either photovoltaic effect (PVE) or photothermoelectric effect (PTE). In multilayer MoS2, the PVE at the MoS2-metal interface dominates in the accumulation regime whereas the hot-carrier-assisted PTE prevails in the depletion regime. Besides, the anomalously large Seebeck coefficient observed in multilayer MoS2, which has also been reported by others, is caused by hot photo-excited carriers that are not in thermal equilibrium with the MoS2 lattice.

Surface-energy triggered phase formation and epitaxy in nanometer-thick Ni1−xPtx silicide films

The formation of ultrathin silicide films of Ni1-xPtx at 450-850 degrees C is reported. Without Pt (x=0) and for t(Ni)= 4 nm, polycrystalline NiSi films form and agglomerate at lower temperatures f ...

SB-MOSFETs in UTB-SOI Featuring PtSi Source/Drain With Dopant Segregation

MOSFETs of both polarities with PtSi-based Schottky-barrier source/drain (S/D) have been fabricated in ultrathin-body Si-on-insulator. The PtSi is formed in the S/D regions without lateral silicide growth under the gate spacers. This design leads to a 30-nm underlap between the PtSi-Si contacts and the gate edges resulting in low drive currents. Despite the underlap, excellent performance is achieved for both types of MOSFETs with large drive currents and low leakage by means of dopant segregation through As and B implantation into the PtSi followed by drive-in annealing at low temperatures.

Interaction of NiSi with dopants for metallic source/drain applications

This work has a focus on NiSi as a possible metallic contact for aggressively scaled complementary metal oxide semiconductor devices. As the bulk work function of NiSi lies close to the middle of Si bandgap, the Schottky barrier height (SBH) of NiSi is rather large for both electron (∼0.65eV) and hole (∼0.45eV). Different approaches have therefore been intensively investigated in the literature aiming at reducing the effective SBH: dopant segregation (DS), surface passivation (SP), and alloying, in order to improve the carrier injection into the conduction channel of a field-effect transistor. The present work explores DS using B and As for the NiSi∕Si contact system. The effects of C and N implantation into Si substrate prior to the NiSi formation are examined, and it is found that the presence of C yields positive effects in helping reduce the effective SBH to 0.1–0.2eV for both conduction polarities. A combined use of DS or SP with alloying could be considered for more effective control of effective SB...

Performance Fluctuation of FinFETs With Schottky Barrier Source/Drain

A considerable performance fluctuation of FinFETs featuring PtSi-based Schottky barrier source/drain is found. The Fin-channels measure 27-nm tall and 35-nm wide. Investigation of similarly processed transistors of broad gate-widths reveals a large variation in the position of the PtSi/Si interface with reference to the gate edge along the gate width. This variation suggests an uneven underlap between the PtSi and the gate from device to device for the FinFETs, since essentially only one silicide grain would be in contact with each Fin-channel at the PtSi/Si interface. The size of the underlap is expected to sensitively affect the performance of the FinFETs.

Magnetoresistance oscillations induced by intersubband scattering of two-dimensional electron gas in Al0.22Ga0.78N/GaN heterostructures

Magnetointersubband scattering (MIS) oscillations of two-dimensional electron gas (2DEG) in Al0.22Ga0.78N/GaN heterostructures have been investigated by means of magnetotransport measurements at low temperatures and high magnetic fields. Double periodic Shubnikov–de Haas oscillations modulated by MIS oscillations have been observed due to the intersubband scattering of the 2DEG at the two lowest subbands in the triangular quantum well at the heterointerface. By using the fast Fourier transform analysis, it is found that the MIS oscillations become slightly weaker with an increase in temperature. From the MIS frequency, the energy separation between the first and the second subbands is determined to be 80 meV. The observation of the MIS effect indicates that the effective masses of the electrons in the first and second subbands are the same in Al0.22Ga0.78N/GaN heterostructures.

Effects of Carbon on Schottky Barrier Heights of NiSi Modified by Dopant Segregation

The presence of carbon at the interface between NiSi and Si has been found to participate in the process of modification of effective Schottky barrier heights using the dopant segregation (DS) method. Carbon alone results in an increased phibn from 0.7 to above 0.9 eV. Boron diffusion in NiSi is inhibited by carbon, and no B-DS at the NiSi/Si interface occurs below 600degC. Above this temperature, B-DS at this interface is evident thus keeping phibn high. The presence of interfacial carbon leads to an increased interfacial As concentration resulting in beneficial effects in tuning phibp above 1.0 eV by As-DS.