First-principles calculations of perovskite thin films

The results of the electronic structure calculations for different surface terminations of SrTiO₃ (1 0 0) perovskite thin films are discussed. These calculations are based on ab initio Hartree–Fock method with a posteriori electron correlation corrections and density functional theory with a number of different exchange-correlation functionals, including hybrid (B3PW, B3LYP) exchange techniques. Results are compared with previous ab initio plane-wave local density approximation and classical shell model calculations. Calculated considerable increase of the Ti–O chemical bond covalency nearby the surface is confirmed by experimental data. We predict also the band-gap reduction, especially for TiO₂ termination.     

Detailed calculations of transient effects in semiconductor injection lasers

Detailed calculations have been carried out of time delay andQ-switching effects in semiconductor lasers using a model described previously, incorporating saturable absorption and loss of optical confinement. The model has been extended to include the high-current limit on theQ-switching region and also the wavelength dependence of threshold current in grating-controlled lasers. In addition, the full rate equations for the electron concentrations in the lasing and absorbing states and for the photon concentration in the lasing mode have been solved by integration in the time domain using a Runge-Kutta numerical procedure. The results illustrate in a relatively simple form the complicated processes occurring during long time delays, abnormal time delays, andQ-switching.     

First-principles calculations of phonon and thermodynamic properties of OsSi2

The structure, lattice dynamics, and some thermodynamic properties of orthorhombic OsSi₂ were investigated using a first-principles density functional theory (DFT). Linear response theory was used to calculate the phonon dispersion relation and phonon density of states for OsSi₂ as well as its infrared and Raman active mode frequencies. In this study, the thermodynamic properties, including vibrational entropy (S_vib), constant-volume specific heat (C_v), and Debye temperature (Θ_D), were predicted theoretically and discussed.     

First-principles calculations of the electronic and structural properties of GaSb

In this paper, we carried out first-principles calculations in order to investigate the structural and electronic properties of the binary compound gallium antimonide (GaSb). This theoretical study was carried out using the Density Functional Theory within the plane-wave pseudopotential method. The effects of exchange and correlation (XC) were treated using the functional Local Density Approximation (LDA), generalized gradient approximation (GGA): Perdew–Burke–Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang91 (PW91), revised Perdew–Burke–Ernzerhof (rPBE), Armiento–Mattson 2005 (AM05) and meta-generalized gradient approximation (meta-GGA): Tao–Perdew–Staroverov–Scuseria (TPSS) and revised Tao–Perdew–Staroverov–Scuseria (RTPSS) and modified Becke-Johnson (MBJ). We calculated the densities of state (DOS) and band structure with different XC potentials identified and compared them with the theoretical and experimental results reported in the literature. It was discovered that functional: LDA, PBEsol, AM05 and RTPSS provide the best results to calculate the lattice parameters (a) and bulk modulus (B₀); while for the cohesive energy (E_coh), functional: AM05, RTPSS and PW91 are closer to the values obtained experimentally. The MBJ, Rtpss and AM05 values found for the band gap energy is slightly underestimated with those values reported experimentally.     

FFT calculation of two-step semiconductor impurity diffusion

The fast Fourier transform (FFT) is used to efficiently calculate an approximation to the second step of the two-step semiconductor impurity atom diffusion. The linearized one-dimensional diffusion equation is assumed with zero oxide growth. The calculation is shown to be a convolution, and the criteria for minimizing aliasing and overlap are outlined. Calculations for erfc (error function) and ion-implanted profiles are shown. Computation time is about 800 ms for a 256-point profile, using APL on an IBM System/370 Model 168 computer. Less than 2-percent error occurs in curve area and surface concentration for typical profiles.     

Hot electron diffusion in fine line semiconductor devices

We present a simple formalism to include hot electron diffusion into device modeling programs. The effectiveness of this method is illustrated for a DMOS-structure and the permeable base transistor. However, the formalism is general and can be applied to any semiconductor device.     

EBIC measurements of small diffusion length in semiconductor structures

The problems arising under submicron diffusion-length measurements by EBIC are discussed. As an example, the results of diffusion-length measurements in GaN are presented. It is shown that fitting the collection efficiency dependence on beam energy is the most reliable method for this purpose. The depth-dose dependence for GaN is calculated by the Monte-Carlo method and its analytical approximation is presented. This expression was verified experimentally by simultaneous fitting of the collected current dependence on beam energy for a few applied bias values. The text was submitted by the authors in English.     

Temperature distribution in semiconductor wafers heated in avertical diffusion furnace

The transient temperature distribution in a row of wafers in a vertical diffusion furnace was calculated as the heating power of the furnace was PID (proportional-integral-derivative)-controlled. Radiative heat transfer was combined with axisymmetric unsteady conduction in wafers and the furnace. With feedforward control of the heating power (which means that when wafers are inserted into the furnace, heater temperature is set higher than the desired heating temperature), the temperature of the wafers reached the heating temperature rapidly. The radiative properties of silicon wafers changed from semitransparent to opaque at 500°C, and the effect of this change on the temperature distribution in the wafers was calculated. It was found that thermoplastic deformation of the wafers is more likely to occur during withdrawal than during insertion     

铁链镶嵌锯齿形氮化硼纳米带半金属铁磁性的第一性原理研究

基于第一性原理,研究了铁链单侧边界钝化型的锯齿形氮化硼纳米带（简称为Fe-terminated ZBNNRs）和铁链连接型的锯齿形氮化硼纳米带（简称为Fe-jointed ZBNNRs）的电子结构及磁性。Fe-terminated ZBNNRs 对于不同带宽的BN纳米带都是半导体型的,而Fe-jointed ZBNNRs 对于不同带宽的BN纳米带则为半金属型。这两种 结构各自的磁性主要都是来自于所掺杂的铁原子。Fe-jointed ZBNNRs 的半金属性源自Fe原子的3d轨道与N原子的2p轨道间的强耦合作用。通过分子动力学模拟,证实了该 结构在常温下可以稳定存在。Fe-jointed-ZBNNRs 对于两种不同自旋方向电子的选择过滤作用可以被应用于自旋电子学器件的设计。其它各种不同的过渡金属所形成的连接型的锯齿形氮化硼纳米带（简称为M-jointed ZBNNRs）既可以是金属型的、半金属型的,也可以是半导体型的。     

Quantum calculations on quantum dots in semiconductor microcavities. Part II

In this work we continue considering solid hybrid systems formed from semiconductor quantum dots and microcavities integrated into a single optical scheme. In the second part, the main emphasis is on the methods of investigation and on the schemes for recording of the spectra and the time dependences of the population energy level, which illustrate the modern control level of the quantum state of these systems.     

Island size distribution under conditions of dislocation-surface diffusion in semiconductor heterostructures

A mechanism of Ostwald ripening of islands under conditions of dislocation-surface diffusion is suggested for semiconductor heterostructures with quantum dots. The island size distribution is calculated for the suggested growth mechanism. Experimental histograms are compared with calculated curves.     

Temperature distribution in semiconductor wafers heated in ahot-wall-type rapid diffusion furnace

Transient temperature distribution was calculated for wafers heated in a new hot-wall-type rapid diffusion furnace. Two-dimensional radiative heat transfer was combined with unsteady conduction in wafers and the furnace. The furnace is composed of parallel plate heaters, and heats wafers to a temperature of about 1000°C. The heaters are divided into four zones and their heating powers are PID-controlled. Two wafers on a holder are inserted vertically from the bottom of the furnace, and heated for three minutes. The calculated results show the wafer temperature approached the desired heating temperature about one minute after insertion, agreeing with experimental results. The average temperature distribution in the wafers during heating is found to be within ±1°C at 1000°C, when the heating power (temperature) of the four zones is properly controlled. The effects of heater temperature, insertion speed, and holder thickness on the temperature distribution in wafers were calculated. The new hot-wall-type rapid diffusion furnace can be used to manufacture future VLSI     

New analytical expressions for dark current calculations of highlydoped regions in semiconductor devices

We studied highly doped quasi-neutral regions of semiconductor devices with position dependent doping concentration in the absence of illumination. An important parameter of a highly doped region is its dark current. To clarify how the doping profile influences the dark current, simple analytical expressions are useful. To this end, we first transformed the transport equations to a simple dimensionless form. This enables us to write already existing analytical expressions in an elegant way. It is demonstrated how, from any analytical dark current expression, a direct counterpart can be derived. Next, we derived a dimensionless form for a nonlinear first-order differential equation for the effective recombination velocity. Starting from the analytical solution of this differential equation for uniformly doped regions and using linearization techniques, we obtained two new simple and accurate expressions for the dark current. The expressions are valid for general doping profiles with different minority carrier transparencies. The exact solution is included between both new approximate solutions. The new expressions are compared with previous approximate solutions     

Bulk carrier lifetime measurement from transient diffusion photocurrent in semiconductor diodes

The theoretical analysis of the transient diffusion photocurrent i_D(t) created in the diode substrate, following weak carrier injection level by a homogeneous photoexcitation of short duration T, shows that the decay i_D(t) can be used in two ways to obtain the substrate bulk carrier lifetime τ_ν. Depending both on the decay times t considered and the values of the substrate parameters τ_ν, D (minority carrier diffusion constant), W (thickness), s (back contact carrier recombination velocity), β (carrier velocity ratio at the p?n junction boundary), then either (1)τ_ν may be deduced from the i_D(t) decay time constant τ if τ is measured at long enough times t>t₁, or else (2)τ_ν is given by the $\text{i}{}_{\mathrm{<mtext>D</mtext>}}\text{(t)×}\text{t}$ product decay time constant θ if θ measured at short enough times t.The numerical illustration of the accuracy and validity conditions of each of the above two ways of exploiting the decay of i_D(t) is given in the case of a P type silicon substrate with a resistivity of 0.2, 1 or 10 Ω cm, W from 50 to 500 μm, τ_ν from less than 0.1 μs to more than 100 μs and various pairs of s (0 or ∞) and β (0 to ∞) values.In practice, the use of a transient photocurrent decay to obtain the diode substrate carrier lifetime also implies a previous analysis of factors such as the device response time constant and transient bias modulation, and the carrier photoexcitation level in the substrate.Experimental results obtained with N⁺P silicon-cells (W = 460 μm and 200 μm) are given and discussed as an illustration of the above study.     

Reliability of semiconductor devices for submarine-cable systems

The Bell System initiated development of semiconductor devices for use in broad-band repeatered coaxial submarine-cable telephone systems in the early 1960's. Development of such devices has continued at varying levels of activity to this date. Now, over a decade later, more than five years of successful operational life have elapsed on the first installed system; one transatlantic system is in operation and several more of equal or greater length are in various stages of construction. Laboratory-like life validation tests have been conducted on all the devices for use in these systems, and up to seven years of history have elapsed on groups of 100 devices representative of the five varieties used in the first system. No failures have been observed either in service or in life validation tests, thereby confirming a FIT rate of better than five. Moreover, variables data for the representative samples aged for seven years indicate that the confirmed FIT rate may be extremely conservative. Silicon diodes aged below breakdown are more stable than the life-test system designed to evaluate their reliability. Silicon diodes aged in breakdown show a linear drift in leakage current which is so small that it is not detectable except with an ultrasensitive test system. Germanium transistors evaluated over this same period show that the change in current gain they exhibit will be substantially less than the goal established for them at the inception of development. Silicon transistors being developed for a new higher capacity system show promise of exceeding the stability of the more extensively evaluated germanium devices. These results have broader implications than their relevance to submarine-cable system performance since they indicate that the reliability which has long been considered to be inherent in semiconductor devices not only has been demonstrably achieved in quantitative terms but can be considered to be designable for future system applications.     

Control of batch processing systems in semiconductor waferfabrication facilities

Loading policies for a batch processing machine, i.e. a machine that can process more than one job at a time, when the arrival times of jobs to the machine are uncertain, are described. The motivation for the study is the structure of process flows and the predominance of batch processing systems in a semiconductor wafer fabrication facility. A two stage serial-batch system with the serial stage (e.g. photolithography) feeding the batch (e.g. furnace) is considered. Machines in the serial stage process one job at a time; further, these machines are subject to failure. A control limit policy for loading the batch machine is assumed, i.e. load if the queue length ⩾Q, else wait until the number of jobs in queue is at least Q. The basic tradeoffs considered are delay (waiting too long) vs. capacity utilization (loading early with very few jobs). An average cost analysis is done and optimized to compute the critical number Q. In an extension to the basic model, the effect of due dates on the critical number is analyzed. Comparison with simulation results is very encouraging     

Theoretical basis for field calculations on multi-dimensional reverse biased semiconductor devices

In this report the theory and the computational methods used to perform numerical field calculations on reverse biased two-dimensional (or three-dimensional with circular symmetry) structures are fully described and completely justified. Finite difference methods are used to approximate Poisson's equation and, together with a depletion region logic, solutions to semiconductor field problems are obtained without the need to solve the complete set of device equations. Two unique aspects of the methods are the depletion logic and the approach taken to handle dielectric interfaces.     

CRC32在光通信系统中的快速计算

文章利用C 编程建立了一个可产生CRC32(32位循环冗余校验)各位并行计算的异或表迭式生成模型,并利用Verilog HDL语言在FPGA(现场可编程门阵列)上进行了验证,结果表明,该模型产生的各位异或表达式适合于高速数据传输情况下CRC32的并行计算.     

Optimized cooling systems for high-power semiconductor devices

Straightforward air cooling of semiconductor devices has gradually been replaced by methods using liquid coolants, especially water cooling. In this paper, more advanced cooling devices for hockey-puck-type and module-type semiconductors are suggested. An established heat sink made of aluminum nitride for the water cooling of hockey-puck-type semiconductors has been used as a basis for the development of high-performance heat sinks for increased heat flux densities. By means of thermal and fluid dynamics simulation tools the internal geometry has been optimized with regard to improved heat transfer and reduced pressure drop. The simulation results have been confirmed by a number of experiments using various measuring techniques. As an alternative cooling method for semiconductor modules, a modified baseplate comprising a number of fins for direct water cooling has been suggested. For an intelligent temperature management control algorithms have been developed, resulting in a prototype application-specific integrated circuit which has been implemented for test purposes