CO/sub 2/ laser processing of alumina (Al/sub 2/O/sub 3/) printed circuit board substrates

We report the results of an investigation of the laser-material interaction processes involved in laser drilling of alumina, through the use of an enhanced peak power (2.5 kW) CO/sub 2/ laser and novel temporal pulse formats. Peak power was varied from 30 W to 2 kW for pulses of constant energy to observe the effect produced on scribe depth. High-speed videography of hole formation has been combined with microscopic analysis to investigate the key processes involved in laser processing of alumina. Plasma screening was observed for short, high peak power laser pulses, and optimal scribing was achieved in the weakly plasma absorbing regime. A new processing technique for scribing alumina has been developed, which exploits the fast response of the laser to produce novel temporal pulse shapes, which can be modified to generate cleaner holes. Scribe speeds of up to 280 mm/spl middot/s/sup -1/ were obtained for scribe holes >200 /spl mu/m deep and 150 /spl mu/m apart, with no material plugging the hole, in 0.635-mm-thick 96% alumina.     

Room temperature photonic crystal defect lasers at near-infraredwavelengths in InGaAsP

Room temperature lasing from optically pumped single defects in a two-dimensional (2-D) photonic bandgap (PBG) crystal is demonstrated. The high-Q optical microcavities are formed by etching a triangular array of air holes into a half-wavelength thick multiquantum-well waveguide. Defects in the 2-D photonic crystal are used to support highly localized optical modes with volumes ranging from 2 to 3 (λ/2n)³. Lithographic tuning of the air hole radius and the lattice spacing are used to match the cavity wavelength to the quantum-well gain peak, as well as to increase the cavity Q. The defect lasers were pumped with 10-30 ns pulses of 0.4-1% duty cycle. The threshold pump power was 1.5 mW (≈500 μW absorbed)     

A 90-nm logic technology featuring strained-silicon

A leading-edge 90-nm technology with 1.2-nm physical gate oxide, 45-nm gate length, strained silicon, NiSi, seven layers of Cu interconnects, and low-/spl kappa/ CDO for high-performance dense logic is presented. Strained silicon is used to increase saturated n-type and p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) drive currents by 10% and 25%, respectively. Using selective epitaxial Si/sub 1-x/Ge/sub x/ in the source and drain regions, longitudinal uniaxial compressive stress is introduced into the p-type MOSEFT to increase hole mobility by >50%. A tensile silicon nitride-capping layer is used to introduce tensile strain into the n-type MOSFET and enhance electron mobility by 20%. Unlike all past strained-Si work, the hole mobility enhancement in this paper is present at large vertical electric fields in nanoscale transistors making this strain technique useful for advanced logic technologies. Furthermore, using piezoresistance coefficients it is shown that significantly less strain (/spl sim/5 /spl times/) is needed for a given PMOS mobility enhancement when applied via longitudinal uniaxial compression versus in-plane biaxial tension using the conventional Si/sub 1-x/Ge/sub x/ substrate approach.     

Hot-carrier dynamics in Ge on single picosecond timescales: Comparing Raman and reflectivity experiments with a self-consistent kinetic model

Through comparisons of picosecond Raman and transient reflection experiments with a comprehensive kinetic model of photo-excited carrier and lattice dynamics in Ge, we demonstrate the ability of these techniques to probe subtle aspects of non-equilibrium carrier dynamics in group IV materials at moderate injected carrier densities. Using material parameters taken from the literature, the temporal evolution of the non-equilibrium optical phonon population generated by the relaxation of photo-excited electrons and holes is obtained by solving a coupled set of Boltzmann equations for the electron and hole particle and thermal currents. The results of the calculation agree, in absolute terms, with the experimentally observed evolution of the non-equilibrium optical phonon population. The calculation also predicts that the hot plasma initially diffuses rapidly away from the sample surface, on a 5 picosecond timescale, and subsequently diffuses much slower as the carrier temperature decays to the lattice temperature, and the density gradient diminishes due to the hot carriers which have already migrated into the material. This prediction is verified by comparison of the calculated change in reflectivity due to the plasma, and picosecond reflectivity measurements performed at room temperature with 575 nm pulses.     

弱P型碲镉汞材料和陷阱模式光导探测器

窄禁带碲镉汞(HgCdTe)为电子和空穴混合导电的多载流子体系材料,特别是对于弱p型材料,由于电子和空穴的迁移率相差大约两个数量级,更容易受到少数载流子电子的干扰,因此单一磁场的霍尔测试无法区分迁移率较低性能较差的n型材料和p型材料.通过变温变磁场的霍尔测试对两种碲镉汞材料的磁输运特性进行了测试区分.另外对由弱p型材料...     

Improvement of responsivity of high-speed infrared detector using hot carriers in semiconductors

A room temperature, high-speed and high-sensitive infrared hot carrier detector using p-type Ge has been investigated at 10.6 μm. The detector is composed of a whisker antenna and a diode contact forming an ohmic contact on p-type Ge. This detector has the merit that one can easily have impedance matching between the antenna and the diode contact without any matching section, so that high sensitivity can be obtained. A voltage sensitivity 16 dB higher than that of metal-insulator-metal (MIM) point contact diode has been observed from this detector.     

应变Si1-xGex pMOSFET反型沟道空穴低场迁移率模型

在考虑应变对SiGe合金能带结构参数影响的基础上,提出了一个半经验的应变Sil-xGex/Si pMOSFET反型沟道空穴迁移率模型.在该模型中,给出了迁移率随应变的变化,并且考虑了界面陷阱电荷对载流子的库仑散射作用.利用该模型对室温下空穴迁移率随应变的变化及影响空穴迁移率的因素进行了分析讨论.     

Growth and electrical properties of the (Si/Ge)-on-insulator structures formed by ion implantation and subsequent hydrogen-assisted transfer

Systematic features of endotaxial growth of intermediate germanium layers at the bonding interface in the silicon-on-insulator structure consisting of buried SiO₂ layer implanted with Ge⁺ ions are studied in relation to the annealing temperature. On the basis of the results for high-resolution electron microscopy and thermodynamic analysis of the Si/Ge/SiO₂ system it is assumed that the endotaxial growth of the Ge layer occurs via formation of a melt due to enhanced segregation and accumulation of Ge at the Si/SiO₂ interface. Effect of germanium at the bonding interface on the Hall mobility of holes in silicon layers with nanometer-scale thickness is studied. It is found that the structures including the top silicon layer with the thickness 3–20 nm and incorporating germanium feature the hole mobility that exceeds by a factor of 2–3 the hole mobility in corresponding Ge-free silicon-on-insulator structures.     

GeOI pMOSFETs空穴迁移率的物理模型

A physical model of hole mobility for germanium-on-insulator p MOSFETs is built by analyzing all kinds of scattering mechanisms, and a good agreement of the simulated results with the experimental data is achieved, confirming the validity of this model. The scattering mechanisms involved in this model include acoustic phonon scattering, ionized impurity scattering, surface roughness scattering, coulomb scattering and the scattering caused by Ge film thickness fluctuation. The simulated results show that the coulomb scattering from the interface charges is responsible for the hole mobility degradation in the low-field regime and the surface roughness scattering limits the hole mobility in the high-field regime. In addition, the effects of some factors, e.g. temperature, doping concentration of the channel and the thickness of Ge film, on degradation of the mobility are also discussed using the model, thus obtaining a reasonable range of the relevant parameters.     

Observation of Nanosecond Carrier Pulses

The present paper describes theory and experiments on the observation of nanosecond carrier pulses in the microwave region. The advancement of microwave nanosecond techniques requires measurement of waveforms which is more accurate than conventional methods. The measuring method described here was developed to satisfy this requirement. The new method, using a synchronous or heterodyne detector, gives accurate and complete information on nanosecond pulse waveforms in the microwave region. Applying this method, we constructed an experimental system to generate and observe the nanosecond pulses in the 11-Gc region. The over-all rise and fall time and delay resolution of this system are as small as 0.5 nsec. Pulse modulators, detectors and filters were measured or adjusted with this experimental system. The experimental results are described in this paper. The pulse generation and observation system developed here is expected to be useful for measuring and adjusting microwave nanosecond pulse devices with accuracy.     

Measurement of hole mobility in heavily doped n-type silicon

Accurate measurements of the mobility (and diffusion coefficient) of minority-carrier holes in Si:P with doping in the 10¹⁹cm^-3range have been done. The technique employed the measurement of diffusion length by means of lateral bipolar transistors of varied base widths, and the measurement of minority-carrier lifetime on the same wafers from the time decay of luminescence radiation after excitation with a short laser pulse. Minority-carrier hole mobility is found to be about a factor of two higher than the mobility of holes as majority carriers in p-type Si of identical doping levels.     

The Effects of High Power Microwave Pulses on Red Blood Cells and the Relationship to Transmembrane Thermal Gradients

Calculations based on an idealized sphericaf model show that the relaxation times of transmembrane thermal gradients in red blood cells, and cells in general, are much less than 1 µs. Heat cannot be stored across the membrane during microwave pulses and only intense pulses can cause substantial transmembrane temperature gradients. Experiments show no hemolysis in red blood cells exposed in vitro to large microwave pulses with peak SAR's of more than 1 kW/g.     

Yb∶YAG陶瓷强化Cr,Yb∶YAG自调Q微片激光器性能研究

报道了通过键合Yb∶YAG激光陶瓷来强化Cr,Yb∶YAG自调Q微片激光器激光性能的研究结果。实现了Yb∶YAG/Cr,Yb∶YAG自调Q微片激光器的激光输出。当吸收抽运功率为7.1W时获得了0.53W的自调Q激光输出,对应的光-光转换效率为7.5%。在实验中获得了脉冲能量大于25μJ、脉冲宽度小于3ns、峰值功率高达9kW的自调Q激光脉冲输出。同时研究了输出耦合镜透射率对Yb∶YAG/Cr,Yb∶YAG自调Q微片激光器激光性能的影响。     

Thermal equilibrium noise of space charge limited current in silicon for holes with field-dependent mobility

Measurements of the limiting white noise of space charge limited hole current in silicon were made at d.c. voltages where the hole mobility becomes field-dependent. The surprising result is established that the hole temperature is equal to the lattice temperature at 110°K within 10 per cent at voltages where the deviations from constant mobility reach 50 per cent. This result contradicts accepted theories relating carrier temperature to field-dependent mobility.     

A logic nanotechnology featuring strained-silicon

Strained-silicon (Si) is incorporated into a leading edge 90-nm logic technology . Strained-Si increases saturated n-type and p-type metal-oxide-semiconductor field-effect transistors (MOSFETs) drive currents by 10 and 25%, respectively. The process flow consists of selective epitaxial Si/sub 1-x/Ge/sub x/ in the source/drain regions to create longitudinal uniaxial compressive strain in the p-type MOSFET. A tensile Si nitride-capping layer is used to introduce tensile uniaxial strain into the n-type MOSFET and enhance electron mobility. Unlike past strained-Si work: 1) the amount of strain for the n-type and p-type MOSFET can be controlled independently on the same wafer and 2) the hole mobility enhancement in this letter is present at large vertical electric fields, thus, making this flow useful for nanoscale transistors in advanced logic technologies.     

Temperature rise of pin diodes from X band pulses

When pin microwave silicon switching diodes are subjected to high-power Xband pulses, the absorbed energy is not distributed uniformly. An apparent peak temperature delay is evidenced when using the junction forward-voltage characteristics as an indicator, and is explained by assuming a model with heat generation in the centre of the i region and the n?i and p?i junctions as sensors.     

Characteristics of Self-Aligned Gate-First Ge p- and n-Channel MOSFETs Using CVD HfO2 Gate Dielectric and Si Surface Passivation

The electrical properties of p- and n-MOS devices fabricated on germanium with metal-organic chemical-vapor-deposition HfO₂ as gate dielectric and silicon passivation (SP) as surface treatment are extensively investigated. Surface treatment prior to high-K deposition is critical to achieve small gate leakage currents as well as small equivalent oxide thicknesses. The SP provides improved interface quality compared to the treatment of surface nitridation, particularly for the gate stacks on p-type substrate. Both Ge p- and n-MOSFETs with HfO₂ gate dielectrics are demonstrated with SP. The measured hole mobility is 82% higher than that of the universal SiO₂/Si system at high electric field (~0.6 MV/cm), and about 61% improvement in peak electron mobility of Ge n-channel MOSFET over the CVD HfO₂ /Si system was achieved. Finally, bias temperature-instability (BTI) degradation of Ge MOSFETs is characterized in comparison with the silicon control devices. Less negative BTI degradation is observed in the Ge SP p-MOSFET than the silicon control devices due to the larger valence-band offset, while larger positive BTI degradation in the Ge SP n-MOSFET than the silicon control is characterized probably due to the low-processing temperature during the device fabrication     

Base resistance and effective bandgap reduction in n-p-nSi/Si1-xGex/Si HBTs with heavy base doping

This paper presents a comprehensive study of the effects of heavy doping and germanium in the base on the dc performance of Si/Si_1-x Ge_x/Si npn Heterojunction Bipolar Transistors (HBTs). The lateral drift mobility of holes in heavily doped epitaxial SiGe bases affects the base sheet resistance while the effective bandgap is crucial for the vertical minority carrier transport. The devices used in this study were Si_1-xGe_x npn HBTs with flat Ge and B profiles in the base grown by Rapid Thermal Chemical Vapor Deposition (RTCVD). Hall and drift lateral hole mobilities were measured in a wide range of dopings and Ge concentrations. The drift mobility was indirectly measured based on measured sheet resistivity and SIMS measurements, and no clear Ge dependence was found. The Hall scattering factor is less than unity and decreases with increasing Ge concentration. The effective bandgap narrowing, including doping and Ge effects, was extracted from the room temperature collector current measurements over a wide range of Ge and heavy doping for the first time. We have observed bandgap narrowing due to heavy base doping which is, to first order, independent of Ge concentration, but less than that observed in silicon, due to the effect of a lower density of states. A model for the collector current enhancement with respect to Si devices versus base sheet resistance is presented     

Modulation characteristics of quantum-dot lasers: the influence of p-type doping and the electronic density of states on obtaining high speed

The influence of p-type modulation doping on self-organized quantum-dot lasers is studied using a quasiequilibrium model that includes the multi-discrete energy levels and the energy levels of the wetting layer. Calculations are presented showing that laser performance can be greatly enhanced through p-doping and that, in contrast to planar quantum-well lasers, the p-doping requirements are moderate. Optimized cavity lengths are found, and the threshold temperature and modulation characteristics are determined for these cavity lengths. The model shows that close energy spacing of the discrete hole levels can severely limit the modulation response, as suggested previously, and that this effect is countered through creation of an excess hole concentration using p-type doping. Good agreement is obtained with the modulation response reported in recent experiments for undoped quantum-dot active regions. The calculations suggest that bandwidths greater than 30 GHz can be obtained with sufficient p-doping. A reduction in the inhomogeneous broadening might increase the laser speed to over 60 GHz.     

A novel germanium doping method for fabrication of high-performance p-channel poly-Si/sub 1-x/Ge/sub x/ TFT by excimer laser crystallization

In this letter, a novel process for fabricating p-channel poly-Si/sub 1-x/Ge/sub x/ thin-film transistors (TFTs) with high-hole mobility was demonstrated. Germanium (Ge) atoms were incorporated into poly-Si by excimer laser irradiation of a-Si/sub 1-x/Ge/sub x//poly-Si double layer. For small size TFTs, especially when channel width/length (W/L) was less than 2 /spl mu/m/2 /spl mu/m, the hole mobility of poly-Si/sub 1-x/Ge/sub x/ TFTs was superior to that of poly-Si TFTs. It was inferred that the degree of mobility enhancement by Ge incorporation was beyond that of mobility degradation by defect trap generation when TFT size was shrunk to 2 /spl mu/m/2 /spl mu/m. The poly-Si/sub 0.91/Ge/sub 0.09/ TFT exhibited a high-hole mobility of 112 cm/sup 2//V-s, while the hole mobility of the poly-Si counterpart was 73 cm/sup 2//V-s.