D. H. Zhang

Influence of silane partial pressure on the properties of amorphous SiCN films prepared by ECR-CVD

Abstract The amorphous silicon–carbon–nitrogen (SiCN) films prepared by the industry-used electron cyclotron resonance chemical vapour deposition (ECR-CVD) at different ratios of silane to the mixture of silane-methane-nitrogen were investigated. The C, Si and N compositions are found to be sensitive to the silane partial pressure. The main bonds in the films are the CN, CN, SiN and their densities vary with the ratio of silane to the gaseous mixture. The SiC bonds are not observable, confirming that the Si and C are bridged by N. In addition, the deposition rate, electrical conductivity, optical bandgap and surface roughness can be monitored by varying the ratio of silane to the gaseous mixture. This alloy is suitable for the light emitting sources and light photodetector for visible light.

Dark current and infrared absorption of p-doped InGaAs/AlGaAs strained quantum wells

The dark current as a function of temperature and infrared absorption of the p-doped In0.15Ga0.85As/Al0.45Ga0.55As multiple quantum well structures grown by molecular beam epitaxy are investigated. The dark current Id of the structure is found to be basically symmetrical over a voltage range from −10 to +10 V. It is about 10−9 A at a bias of 1 V at 80 K, more than two orders of magnitude lower than that reported for p-doped GaAs/AlGaAs QW structures with the same size. It is also found that Id is proportional to T exp[−(EC–EF)/kT] at 70 K and above while at temperatures below 30 K it does not change significantly. The EC–EF decreases with the increase in bias in an exponential form, due likely to energy bandgap bending. A strong infrared absorption peaked at a wavelength of 10.7 μm is in excellent agreement with the estimated value of 10.4 μm.

Effects of nitrogen fraction on the structure of amorphous silicon–carbon–nitrogen alloys

Abstract The silicon–carbon–nitrogen (SiCN) alloys prepared by DC magnetron sputtering at room temperature with graphite and silicon targets at different nitrogen partial pressure were systematically investigated. It was found that a high nitrogen fraction in the nitrogen–argon gaseous mixture enhances the incorporation of C and N, but reduces the incorporation of Si. The SiC, SiN, SiSi, CN, CN, CN, CO, CC, CC and NH bonds can all be observed in the alloys. The CN, CC and CN bonds dominate the structure of the alloys, while the SiC, SiSi and SiN bonds are less significant. As the N2/(N2+Ar) ratio increases, the densities of the SiC, SiN and CN bonds decrease, while those of the CN, CC, CC and CN bonds increase. In addition, the deposition rate is found to monotonically increase with the nitrogen partial pressure, probably due to the enhanced incorporation of nitrogen and carbon.

Characterization of beryllium-doped molecular beam epitaxial grown GaAs by photoluminescence

We report a detailed investigation of the Be-doped layers grown at a high AsGa flux ratio as a function of hole concentration using room and low temperature photoluminescence (PL). It has been found that the change of PL spectra with doping differs from that observed in Zn-doped layers grown by liquid phase epitaxy (LPE). The luminescence intensity increased monotonically with free hole concentration. The PL full widths at half maximum (FWHM) at room temperature and 4 K are proportional to the log of doping level and can be used to estimate free hole concentration in the range 1017 < p < 2.25 × 1020 cm−3. In addition, the PL peak energy EM at room temperature was found to drop slowly with hole concentration up to 2.25 × 1020 cm−3 while EM at 4 K did not change significantly up to 3 × 1018 cm−3 and dropped drastically thereafter. The former could be explained by band tail transitions, and the latter, we suggest, is most likely a result of band-acceptor transitions.

Direct patterning of high density sub-15 nm gold dot arrays using ultrahigh contrast electron beam lithography process on positive tone resist

Ultrahigh density nanostructure arrays with controlled size and position have promised a variety of potential applications. However, their practical realization is often hindered by the amount of resources required for large-scale fabrication. Using an ultrahigh contrast electron beam lithography process, we show ultrahigh resolution and high aspect ratio patterning capability which can be done at an exposure dose lower than 100 μC cm(-2). In particular, the high aspect ratio of dot arrays on 110 nm thick resist is confirmed by a standard lift-off process of 20 nm thick gold nanodots at sub-15 nm feature size and 40 nm pitch. The smallest gold nanodot size from our experiment is 11 nm.

Effects of arsenic beam equivalent pressure on InGaAsP grown by solid source molecular beam epitaxy with continuous white phosphorous production

Abstract We report the effects of arsenic beam equivalent pressure on lattice mismatch, electrical properties, surface roughness and morphology of InGaAsP grown by solid source molecular beam epitaxy using valve arsenic and phosphorous cracker cells with continuous white phosphorous production. Arsenic is found to have a higher sticking coefficient than phosphorous in almost all arsenic pressure employed in the growth. The incorporation of arsenic is found to fit a polynomial expression, Y =1.56 R −0.59 R 2 , with the beam equivalent pressure ratio R = f As /( f As + f P ). The incorporated arsenic elements significantly affect lattice mismatch and electrical properties. They also dominate surface construction of the quaternary material.

Experimental demonstration of coupled-resonator-induced-transparency in silicon-on-insulator based ring-bus-ring geometry

We experimentally demonstrate coupled-resonator-induced-transparency (CRIT) phenomenon in ring-bus-ring (RBR) geometry synergistically integrated with Mach-Zehnder interferometer (MZI). The RBR consists of two detuned resonators indirectly coupled through a center bus waveguide. The transparency is obtained by increasing the light intercavity interaction through tailoring the RBR phase response while ensuring balanced MZI operation. In this work, a CRIT resonance with a quality factor of ~18,000 is demonstrated with cavity size detuning of ~0.035% and power coupling of ~60%, which are in good agreement with the theory.

Physical properties of InGaAsP/InP grown by molecular beam epitaxy with valve phosphorous cracker cell

InGaAsP films grown on InP substrate by solid source molecular beam epitaxy (SSMBE) using a valve phosphorous cracker cell are investigated. It is found that the films grown at flux ratios f As /(f As + f p ) from 0.45 to 0.50 show a superior quality. It is also found that As pressure plays a crucial role in the scattering process; for the films grown at higher arsenic beam pressure (BEP), the Hall mobility μ is dominated by impurity scattering, polar phonon scattering and alloy scattering. For the films with high quality, optical scattering and alloy scattering dominate the mobility. The exponent of T for the films grown at low BEP is found to be as high as 2.54, which cannot be explained by impurity scattering alone. It is believed that, in addition to the impurity-related scattering, some defects associated with As vacancies also significantly contribute to the scattering, especially at low temperatures.

Phase singularity of surface plasmon polaritons generated by optical vortices

We demonstrate an experimental result that shows the phase singularity of surface plasmon waves generated by the direct transform of optical vortices at normal incidence focused on a structureless metal surface. The near-field two-dimensional intensity distribution near the focal plane is experimentally examined by using near-field scanning optical microscopy and shows a good agreement with the finite-difference time-domain simulation result. The experimental realization demonstrates a potential of the proposed excitation scheme to be reconfigured locally with advantages over structures milled into optically thick metallic films for plasmonics applications involving plasmonic vortices.

Metal contacts to n-type AlGaAs grown by molecular beam epitaxy

Abstract We report for the first time the barrier heights of Cu, Ni, Ag, Ti on etched n-type Al 0.33 Ga 0.67 As and their dependence on annealing temperature with I–V and C–V techniques. The barrier heights of Al and Au, measured for comparison, are 0.96 and 1.06 eV, respectively, in excellent agreement with the results reported previously. The barrier heights of the Cu, Ni, Ag and Ti/nAl 0.33 Ga 0.67 As diodes are found to be 1.08, 0.90, 0.87 and 0.87 eV, respectively. It is observed that the barrier heights for Al, Au, Cu and Ti contacts monotonically decrease with annealing temperature. For the Ag and Ni contacts, however, they become higher after being annealed at 473 K for 10 min and become lower thereafter, accompanied by a change of their ideality factors in opposite direction. The barrier heights extrapolated from C–V measurements for all metals studied are higher than that deduced from I–V data, and become higher after annealing at high temperatures, indicating the existence of a thin oxide layer at interface and broadening of the oxide after annealing. Our results can be qualitatively explained by the quality of contact and defects created at the semiconductor surface due to interdiffusion.