Narrow Results

This chapter discusses two limitations which restrict the design of modern electronic circuits. The first is how small a circuit can be made, which is ultimately governed by the size of the individual electrons inside a circuit. Physicists are probing this limit, and in doing so are finding ways to control with great precision the movement of single electrons. The second limitation is the operational frequency of electronic systems, which is currently restricted to frequencies below approximately 1 THz. At frequencies in the terahertz range, the concepts governing electronic circuits design start to merge with concepts from the field of photonics. Experiments which are probing these two limitations are discussed in the context of their implications for future microelectronic circuit design.

Recent progress of radiation therapy is rapid. However, medical accidents like the irradiation of over and under dose occur frequently. To reduce these accidents and to increase accuracy of radiation therapy, we are developing an implantable real time microdosimeter system. CdTe semiconductor is used as a detector. And the doses of radiation are monitored by measuring the magnetic field converted from the current. We investigated the relationship between dose rate and current value from CdTe semiconductor(4mm×4mm×0.5mm). The data showed that 70 to 90 nA of electric current is proportionally generated from the CdTe semiconductor when the LINAC is working in air by the dose rate of 1 ~6Gy/min. In addition, the proportion of irradiate dose and the current was confirmed in subaqueous condition(15cm in depth). To investigate the influence of a magnetic field on a human body, we calculated the tolerance frequency to human body using FEM simulation method. The data showed that the sending and receiving of data as a frequency of magnetic field should be set 100MHz or less. We are now miniaturizing the dosimeter circuit based on these data.

The near band-edge polarized optical optical absortion spectra of EuTe at low temperatures and high magnetic fields were investigated. The samples were grown by MBE on BaF₂ substrates, and the thickness varied in the 0.18-2.0 µm range. At high magnetic fields, the well-known 4f⁷ → 4f⁶5d(t_2g) optical transition splits into two well resolved lines at σ⁺ and two lines for σ−. These lines can be described by localized transitions tunable by the d − f exchange interaction, with a quadratic dependence on the intensity of the external magnetic field. Comparative measurements of the magnetization and the optical absorption as a function temperature provides a further test of the model of a localized excitation extending over a few lattice sites.

Doped superlattices of GaAs/Al_0.21Ga_0.79As composition, with a carrier concentration of n = 1.4 × 10¹²cm⁻² and n = 1.7 × 10¹²cm⁻² per superlattice period, where studied by photoluminescence in high magnetic fields. The photoluminescence intensity at fixed photon energies showed weak oscillations. From the oscillatory photoluminescence the superlattice miniband energy width and the renormalized bandgap were deduced.

We theoretically propose that the spin Hall effect occurs in p-type semiconductors even without an aid of impurity scattering. An effect of disorder is also investigated. We also discuss a criterion for nonzero spin Hall effect. With this criterion, we predict that some band insulators have nonzero spin Hall effect.

The simulation of semiconductor devices has become a standard tool in the construction process. A very detailed description of the transport processes in semiconductors is provided by kinetic transport models. However, the numerical approaches to this kind of equation which have been presented so far are not competitive with respect to the computation time to other methods. In this paper, we investigate approaches to speed up numerical methods like box methods and WENO schemes for solving the Boltzmann transport equation.

EUV lithography is the exposure technology in which even 15 nm node which is the limit of Si device can be achieved. Unlike the conventional optical lithography, this technology serves as a reflection type optical system, and a multilayer coated mirror is used. Development of manufacturing equipment is accelerated to aim at the utilization starting from 2011. The critical issues of development are the EUV light source which has the power over 115 W and resist with high sensitivity and low line edge roughness (LER).

Rare earth-based compounds exhibit excellent properties for application in solar cells such as luminescence and photo-electric transformation due to their 4f electronic structures. In this paper, a novel Yb-doped CuIn_1-xYb_xTe₂ semiconducting compound is synthesized and its crystal structure and optimal property are analyzed using X-ray diffraction (XRD) and ultraviolet and visible (UV-Vis) spectrophotometer. The experiment results demonstrate that the doping of ytterbium into CuInTe₂ (CIT) can stabilize the chalcopyrite structure and the lattice parameters highlights a fluctuating phenomenon with Yb doping in CIT. The band gap E_g corresponds to 1.25eV and 1.50 eV before and after 0.1 mole Yb doping respectively. Therefore, the doping of Yb into CuInTe₂ improves the absorption spectra with special frequencies.

The following sections are included:

• Ultrafast Processes in Semiconductors
• Ultrafast Processes in Metal Nanoparticles
• Ultrafast Processes in Quantum Dots
• References

Structural and bandgap properties of Be_xZn_1-xO alloy films were investigated by first-principles calculations. The alloy phase segregation caused by large lattice distortion and bowing parameter was predicted at intermediate Be content and was latterly confirmed by X-ray diffraction (XRD) measurement. In the case of the phase segregated BeZnO, two absorption edges, a weak absorption shoulder and a near band edge absorption, were observed in our calculated optical absorption spectra. The shoulder absorption trends to be eliminated by suppressing the phase segregation of BeZnO. By the further study on detailed density of states (DOS), the weak non-band-edge absorption shoulder is essentially originates from the electrons transferring from the 2p orbitals of oxygen atoms nearby the grain boundary between ZnO and BeO crystallites to the 4s orbitals of all of Zn atoms in the system. Such optical absorption spectra features provide a new phenomenon and mechanism in the novel alloy system BeZnO.

Material characterization is challenged by continuously decreasing device dimensions placing significant demands on characterization instruments and measurement interpretation. Numerous techniques exist and a few are highlighted here. Some of these have existed for a long time, while others have only emerged from the laboratory recently. Generally they are more user-friendly and have reasonable turn-around times. The trend in many techniques is clearly toward characterization of smaller dimensions. Among the myriad of characterization techniques in use today, I will discuss recent advances in transmission electron microscopy (TEM), electron holography, magnetic exchange force microscopy (MExFM), atom probe ion field ion microscopy, and X-ray tomography. They have made significant advances in the last few years and in some cases have produced very impressive results. For example, TEM is now able to generate images with 0.05 nm resolution, allowing display of individual atoms. MExFM in conjunction with magnetic fields has demonstrated vertical resolution of 0.0015 nm. Helium ion microscopy is also highlighted because it contributes a new application of ion beams, which had been largely the domain of Rutherford backscattering. Progress in developing further advances in nm dimensional characterization will, no doubt, continue to satisfy the demand for such measurements in the future.

Power semiconductor devices are important for numerous applications with power conversion being an important one. Wide energy gap semiconductors SiC and GaN have properties that make them attractive for such applications. Among these properties are high thermal conductivity, high breakdown electric field, wide energy gap, low intrinsic carrier concentration, high thermal stability, high saturation velocity and chemical inertness. These lead to low on-resistance, high breakdown voltage, high frequencies, small volume, and small passive inductors and capacitors. These desirable properties are offset by the higher material costs and higher defect densities. Although wide energy gap devices have been in development for many years, only recently have they become available commercially. Their main competition is silicon power devices with breakdown voltages up to 8000 V and very high surge current capacity. However, silicon power devices are approaching their material limits and wide energy gap devices are beginning to have an impact in the power electronics space. SiC has the advantage of substrates with diameters approaching 150 mm and the ability to grow thermal SiO₂. GaN has the heterojunction advantage, but no viable substrate technology. In fact, a large portion of SiC production is used for GaN substrates. GaN material development has also benefited significantly from the development of optical devices, e.g., light-emitting diodes and lasers.