D. Z. Chi

Sulfur-Induced PtSi:C/Si:C Schottky Barrier Height Lowering for Realizing N-Channel FinFETs With Reduced External Resistance

In this letter, sulfur (S) segregation was exploited to attain a record-low electron barrier height (PhiB N) of 110 meV for platinum-based silicide contacts. Sulfur-incorporated PtSi:C/Si:C contacts were also demonstrated in strained FinFETs with Si:C source/drain stressors. Incorporation of sulfur at the PtSi:C/Si:C interface in the source/drain regions of FinFETs provides a 51% improvement in external resistances and a 45% enhancement in drive current as compared to devices without S segregation. The remarkable reduction in PhiB N is explained using charge transfer and dipole formation at the silicide/semiconductor interface with S segregation.

Piezotronic Effect on the Transport Properties of GaN Nanobelts for Active Flexible Electronics

The transport properties of GaN nanobelts (NBs) are tuned using a piezotronic effect when a compressive/tensile strain is applied on the GaN NB. This is mainly due to a change in Schottky barrier height (SBH). A theoretical model is proposed to explain the observed phenomenon.

Assignment of deep levels causing yellow luminescence in GaN

The deep levels in GaN associated with yellow luminescence transitions have been investigated using photoluminescence, Hall measurements, and deep level transient spectroscopy (DLTS). Hall measurements on Si-doped GaN show the presence of donor levels at ∼18, ∼35, and ∼70 meV, which are respectively associated with the Si shallow donors, O impurities, and the nitrogen vacancies (VN). DLTS measurements, on the other hand, reveal trap levels at Ec−0.1 eV, Ec−(0.2–0.24) eV, and Ev+0.87 eV. The trap level at Ec−0.1 eV obtained from DLTS can be correlated to the 70 meV deep donor (VN) obtained from Hall measurements. The deep donor band at Ec−(0.2–0.24) eV is attributed to the ON related defect complex decorated along dislocation sites while the hole level at Ev+0.87 eV is attributed to the Ga vacancy (VGa). Thermal annealing at 750 °C in nitrogen ambient results in reduction of yellow luminescence, which could be due to decrease in the concentration of VN and ON-related defect complexes. From these observatio...

Nanocrystal engineering of sputter grown CuO photocathode for visible light driven electrochemical water splitting

Cupric oxide (CuO) thin film was sputtered onto fluorine-doped tin oxide (FTO) coated glass substrate and incorporated into a photoelectrochemical (PEC) cell as a photocathode. Through in situ nanocrystal engineering, sputtered CuO film shows an improvement in its stability and photocurrent generation capability. For the same CuO film thickness (150 nm), films deposited at a sputtering power of 300 W exhibit a photocurrent of ∼0.92 mAcm(-2) (0 V vs RHE), which is significantly higher than those deposited at 30 W (∼0.58 mAcm(-2)). By increasing the film thickness to 500 nm, the photocurrent is further enhanced to 2.5 mAcm(-2), which represents a photocurrent conversion efficiency of 3.1%. Systematic characterization using Raman, XRD, and HR-TEM reveals that the high sputtering power results in an improvement in CuO film crystallinity, which enhances its charge transport property and, hence, its photocurrent generation capabilities.

Novel Epitaxial Nickel Aluminide-Silicide with Low Schottky-Barrier and Series Resistance for Enhanced Performance of Dopant-Segregated Source/Drain N-channel MuGFETs

We have developed a novel epitaxial nickel-aluminide silicide (NiSi_2-xAl_x) to reduce the Schottky-barrier height (SBH) and series resistance in n-channel MuGFETs with dopant-segregated Schottky-Barrier source/drain (DSS). 10% substitutional incorporation of Al in the Si matrix at the silicide-Si interface leads to a 37% reduction in the intrinsic SBH of nickel silicide. A further 42% effective reduction in the DSS SBH was attained with the combination of NiSi_2-xAl_x and DSS technology. Saturation drive current enhancement of 94% for NiSi_2-xAl_x DSS MuGFETs over NiSi DSS MuGFETs was achieved, attributed to SBH lowering, series resistance reduction and possibly silicide strain effects. As a result, an excellent drive current of 882 muA/mum at V_GS-V_T =V_DS = 1.2 V was achieved for NiSi_2-xAl_xDSS MuGFETs with 55 nm gate length.

F-enhanced morphological and thermal stability of NiSi films on BF2+-implanted Si(001)

The morphological and thermal stability of conducting NiSi films formed on Si(001) are significantly enhanced by pre-implantation of the Si wafer with BF2+. In the absence of F, the maximum silicidation temperature Tmax is 650 °C; higher temperatures lead to the formation of the competing high-resistivity NiSi2 phase. Tmax, however, is increased to ⩾750 °C during NiSi formation on Si(001) implanted with 20 keV BF2+ at a dose of 5×1015 cm−2. The observed enhancement in NiSi thermal stability is due to F segregation to the silicide/Si(001) interface and silicide grain boundaries, which retards NiSi grain growth, leading to much smoother layers, and inhibits NiSi2 nucleation.

Effects of AlAs interfacial layer on material and optical properties of GaAs∕Ge(100) epitaxy

GaAs∕AlAs∕Ge(100) samples grown at 650°C with AlAs interfacial layer thickness of 0, 10, 20, and 30nm were characterized using transmission electron microscopy, secondary ion mass spectrometry (SIMS), and photoluminescence (PL) techniques. SIMS results indicate that the presence of an ultrathin AlAs interfacial layer at the GaAs∕Ge interface has dramatically blocked the cross diffusion of Ge, Ga, and As atoms, attributed to the higher Al–As bonding energy. The optical quality of the GaAs epitaxy with a thin AlAs interfacial layer is found to be improved with complete elimination of PL originated from Ge-based complexes, in corroboration with SIMS results.

Interfacial characteristics and band alignments for ZrO2 gate dielectric on Si passivated p-GaAs substrate

The interfacial characteristics and band alignments of high-k ZrO2 on p-GaAs have been investigated by using x-ray photoelectron spectroscopy and electrical measurements. It has been demonstrated that the presence of Si interfacial passivation layer (IPL) improves GaAs metal-oxide-semiconductor device characteristics such as interface state density, accumulation capacitance, and hysteresis. It is also found that Si IPL can reduce interfacial GaAs-oxide formation and increases effective valence-band offset at ZrO2∕p-GaAs interface. The effective valence-band offsets of ZrO2∕p-GaAs and ZrO2∕Si∕p-GaAs interfaces are determined to be 2.7 and 2.84eV, while the effective conduction-band offsets are found to be 1.67 and 1.53eV, respectively.

Effect of oxygen evolution catalysts on hematite nanorods for solar water oxidation

Photochemical deposition of Co and Ni based oxygen evolution catalysts on hematite nanorods cathodically shifted the onset potential of photocurrent near to the flat band potential of hematite. A 9.5 fold enhancement in the photocurrent density at 0.86 V vs. RHE compared to the parent hematite photoanode was observed with the Ni-Bi/Fe(2)O(3) photoanode.

Photovoltaic characteristics of p-β-FeSi2(Al)/n-Si(100) heterojunction solar cells and the effects of interfacial engineering

Heterojunction solar cells with Al-alloyed polycrystalline p-type β-phase iron disilicide [p-β-FeSi2(Al)] on n-Si(100) were investigated. The p-β-FeSi2(Al) was grown by sputter deposition and rapid-thermal annealing. Photocurrent of ∼1.8 mA/cm2 and open-circuit voltage of ∼63 mV were obtained for p-β-FeSi2(Al)/n-Si(100)/Ti/Al control cells with indium-tin-oxide (ITO) top electrode. Open-circuit voltage increased considerably once thin Al layer was deposited before amorphous-FeSi2(Al) deposition. Furthermore, device performances were found to improve significantly (∼5.3 mA/cm2 and ∼450 mV) by introducing germanium-nitride electron-blocking layer between ITO and p-β-FeSi2(Al). The improvement is attributed to the formation of epitaxial Al-containing p+-Si at p-β-FeSi2(Al)/n-Si(100) interface and suppressed back-diffusion of photogenerated electrons into ITO.