Papers by Keyword: Photonics

Abstract: The synthesis and characterization of spin-coated Al-doped ZnO (AZO) thin films with varying Al concentrations (0%, 5%, 10%, 15% and 20%) onto glass substrates have been demonstrated in this paper. The structural, electrical and optical properties of the spin-coated thin films have been investigated by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) analysis, Van Der Pauw method and UV-visible spectroscopy. The EDX study shows well-defined peaks which confirm the presence of only Zn, O and Al and no other impurities in the films. The increase of Al and decrease of Zn weight percentages with increasing doping level confirms the effective substitution of Zn by Al. SEM of the surfaces of the films shows that undoped ZnO films contain particle agglomeration which is reduced with Al doping and the surfaces of the films gradually became more uniform. The thickness of the AZO films varied from 86 to 699 nm with increasing Al doping concentration. The electrical conductivity of the films increased up to ~ 7 × 10^-2 (Ω.cm)^-1 due to doping with 5% Al concentration. The optical transmittance highly increased above 95% in the visible range with the introduction of Al dopant and it kept rising with the increase of Al concentration. The optical energy band gap of undoped ZnO increased from 3.275eV to 3.342 eV with 5% Al doping.

Abstract: Modern electronics is based on semiconductor nanostructures in practically all main parts: from microprocessor circuits and memory elements to high frequency and light-emitting devices, sensors and photovoltaic cells. Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) with ultimately low gate length in the order of tens of nanometers and less is nowadays one of the basic elements of microprocessors and modern electron memory chips. Principally new physical peculiarities of semiconductor nanostructures are related to quantum effects like tunneling of charge carriers, controlled changing of energy band structure, quantization of energy spectrum of a charge carrier and a pronounced spin-related phenomena. Superposition of quantum states and formation of entangled states of photons offers new opportunities for the realization of quantum bits, development of nanoscale systems for quantum cryptography and quantum computing. Advanced growth techniques such as molecular beam epitaxy and chemical vapour epitaxy, atomic layer deposition as well as optical, electron and probe nanolithography for nanostructure fabrication have been widely used. Nanostructure characterization is performed using nanometer resolution tools including high-resolution, reflection and scanning electron microscopy as well as scanning tunneling and atomic force microscopy. Quantum properties of semiconductor nanostructures have been evaluated from precise electrical and optical measurements. Modern concepts of various semiconductor devices in electronics and photonics including single-photon emitters, memory elements, photodetectors and highly sensitive biosensors are developed very intensively. The perspectives of nanostructured materials for the creation of a new generation of universal memory and neuromorphic computing elements are under lively discussion. This paper is devoted to a brief description of current achievements in the investigation and modeling of single-electron and single-photon phenomena in semiconductor nanostructures, as well as in the fabrication of a new generation of elements for micro-, nano, optoelectronics and quantum devices.

Abstract: A novel infrared photodiode based on a graphene/n-type silicon heterojunction is explored. The heterojunction photodiode of interest has a large Schottky barrier that results in a low dark current. Graphene serves as the absorbing medium at a wavelength for which silicon is transparent. Under infrared illumination, photo-excited electrons in the graphene gain energy and thus have a greater probability to overcome the barrier and contribute to the photocurrent. We have demonstrated photodiode operation of a graphene/n-Si heterojunction at 1.3 and 1.55 μm wavelength, with 14% internal quantum efficiency and 1.5 pW/Hz^1/2 noise-equivalent power, for potential use in silicon photonics.

Abstract: We fabricated and characterized record small microdisk resonators in thin (210 nm) 3C-SiC film grown on Si (100) substrate. It was found to support high quality factor whispering gallery modes at visible wavelengths. We demonstrated room temperature coupling of these modes to the intrinsic photoluminescence of 3C-SiC at room temperatures and identified their polarization. Finally, we discussed applications for quasi-phasematched second harmonic generation from infrared visible wavelengths.

Abstract: The particular physical functions of quantum-sized silicon have been investigated, along with exploration of their potential device applications. A strong confinement effect fully modifies the original optical, electrical, and thermal properties of bulk silicon. A discussion regarding their control and applications is presented, which addresses blue phosphorescence, enhanced photoconduction, operation of a ballistic electron emitter in solutions, and digital drive of a thermo-acoustic sound emitter.

Abstract: In the broadband communication network, the wavelength-division-multiplexed (WDM) system is widely used to maximize the information that the signals can carry. As a result, the number of channels which are carried by different optical wavelengths in the WDM optical fiber network also keeps increasing. To separate the huge number of different wavelength signals, optical filter is required. The optical filter based on semiconductor has been widely studied due to the maturation of semiconductor fabrication technology and that it is possible to integrate the filter with the stable semiconductor devices such as laser diodes and MOSFETS. The tunable optical filter is basically a selective optical resonator that only allows the resonant modes passing through. Various mechanical methods are studied to achieve the tunable effect by tuning the physical structure of the filter; however, there is not much research on how the semiconductor material will affect the tuning function. In this paper, the author studied the influence of refractive index of the multi-silicon-slabs on the filter, whereby the tuning of refractive index is reached by thermal effect. It is found by simulation that when heating the silicon slabs, the increasing refractive index of silicon will lead to a shift of the resonant mode wavelength. This shift is almost linear with the change of the temperature, which is about 1nm with every 20K temperature increase. For certain devices, the result of the simulation showed it is possible to tune the resonant mode from C band to L band in the Fiber Optical Communication.

Abstract: In this paper, techniques developed in the fabrication of nano-structures such as photonic gratings and vertical tube structures are presented for fabrication development that is applicable in the field of MEMS/NEMS technology – particularly for the optical integrated circuits [1] and sensor devices [2]. In such applications, not only is the resolution enhancements important, it is also often imperative that Critical Dimensions Uniformity (CDU) be kept as low as possible - since device performance often times scales directly with structural dimensions and its accuracy [3]. In this regard, techniques such as phase shift masking, off-axis illumination, optical proximity corrections, and also multiple patterning and resist ashing etc needs to be employed. This, not only increases the number and complexity of processing steps; it (at the same time) implicates other specifications such as illumination apertures, mask designs, optical proximity simulations, tool overlay tolerances etc. Coupled with additional non-CMOS requirements of atypical pattern shapes and densities, such as rings, horse-shoe shapes, sharp edges etc, a comprehensive study of the flexibilities involved with micro-lithography needs to be carried out for novel design prototyping. Here, the above described are illustrated, using examples of (i) a photonic gratings structure patterned with sharp edges, and (ii) a vertical-tube switch device structure, which are presented and discussed for their fabrication techniques and measurement results.

Abstract: The optical sensor achieves its sense function generally by measuring the change of intensity or the phase of the light beams. Compared to conventional sensor types, the optical sensor enjoys the advantages such as great sensitivity, wide dynamic sense range and multiplexing capabilities. In recent years, MEMS technology is widely used on the design of optical sensor due to the small feature of MEMS, which could be high sensitive with tiny change of the detected objective. In this paper, instead of observing the change of intensity and phase, the author studied how the shift of wavelength spectrum can be utilized to sense the physical change of the object such as the pressure, vibration, velocity and electrical field. The author designed and simulated a FP-resonator-like structure which consists of 2 resonant cavities with 2 multi-layer mirrors located on two ends and 1 multi-layer mirror in the middle of the two cavities. The mirror in the middle is movable by physical pressure. In the simulation, it was found that this structure is able to have certain wavelength light resonate inside the cavities. The resonant mode will shift 1nm when the mirror in the center moves forward/backward for every 14nm, which is sensitive enough to detect the small change of the objectives.

Abstract: There is a clear and increasing interest in short time thermal processing far below one second, i.e. the lower limit of RTP (Rapid Thermal Processing) called spike annealing. It is the world of processing in the millisecond or nanosecond range. This was driven by the need of suppressing the so-called Transient Enhanced Diffusion in advanced boron-implanted shallow pnjunctions in the front-end silicon chip technology. Meanwhile the interest in flash lamp annealing (FLA) in the millisecond range spread out into other fields related to silicon technology and beyond. This paper reports shortly about the restart in flash lamp annealing of the Rossendorf group in collaboration with the Mattson group and further on recent experiments regarding shallow junction engineering in germanium, annealing of ITO (indium tin oxide) layers on glass and plastic foil to form an conductive layer as well as investigations which we did during the last years in the field of wide band gap semiconductor materials (SiC, ZnO). Moreover recent achievements in the field of silicon-based light emission basing on Metal-Oxide-Semiconductor Light Emitting Devices will be reported. Finally it will be demonstrated that the basic principle of short time thermal processing, i.e. surface heating on a colder bulk, features also advantages regarding the casting of lead sheets to produce organ pipes in the spirit of the 17th century.

Abstract: The high density of interface electron traps in the SiC/SiO2 system, near the conduction band of 4H-SiC, is often ascribed to graphitic carbon islands at the interface, although such clusters could not be detected by high resolution microscopy. We have calculated the electronic structure of a model interface containing a small graphite-like precipitate of 19 carbon atoms, with a diameter of ~7 Å, corresponding to the experimental detection limit. The analysis of the density of states shows only occupied states in the band gap of 4H-SiC near the valence band edge, while carbon related unoccupied states appear only well above the conduction band edge.