碳纳米管蒸发特性及其对场发射性能的影响

为了探究场发射阴极电流的跌落机制,采用四极质谱仪分析的方法研究高温蒸发对阴极场发射性能的影响。实验结果表明：碳纳米管阴极在1173 K以上温度时开始蒸发出碳;在1373 K高温下连续蒸发100小时,碳纳米管阴极的开启场强增加21.7%,阈值场强增加31.7%,增强因子减小16.2%,功函数增加11.9%。扫描电镜（SEM）和能量色散X射线光谱仪（EDX）分析显示：增大的功函数和减小的场增强因子降低了阴极的场发射性能。阴极材料的蒸发是阴极电流跌落的重要原因。     

A numerical analysis of submicrometer InP-transferred electrondevices

A numerical technique combining the Boltzmann transport equation and a cathode mobility model has been used to simulate the nonuniform field configurations and the static and dynamic transport behavior of submicrometer InP-transferred electron devices (TEDs). Significant interrelated controlling features for the 70-230-GHz operation of these devices have been analyzed. They determine the manifestation of the current instabilities in the following ways: (1) the length has a significant effect on the velocity-field characteristics for submicrometer TEDs, and thus on the oscillation threshold as well as the upper-frequency limit for transit-time oscillations; and (2) the cathode mobility (boundary condition), doping density, and bias acting together have a dominant effect on the threshold and cutoff of the current instability. The numerical results can be used to determine the optimum efficiency and frequency of actual devices     

Temperature dependence of the lasing characteristics of the 1.3 µm InGaAsP-InP and GaAs-Al0.36Ga0.64As DH lasers

We report here our experimental observations on the temperature dependence of threshold current, carrier lifetime at threshold, external differential quantum efficiency, and gain of both the 1.3 μm InGaAsP-InP and GaAs-AlGaAs double heterostructure (DH) lasers. We find that the gain decreases much faster with increasing temperature for a 1.3 μm InGaAsP DH laser than for a GaAs DH laser. Measurements of the spontaneous emission observed through the substrate shows that the emission is sublinear with injection current at high temperatures for the 1.3 μm InGaAsP DH laser. Such sublinearity is not observed for GaAs DH lasers in the entire temperature range 115-350 K. The experimental results are discussed with reference to the various mechanisms that have been proposed to explain the observed temperature dependence of threshold of InGaAsP DH lasers. We find that inclusion of a calculated nonradiative Auger recombination rate can explain the observed temperature dependence of threshold current, carder lifetime at threshold, gain, and also the sublinearity of the spontaneous emission with injection current of the 1.3 μm InGaAsP-InP DH laser. Measurement of the nonradiative component of the carrier lifetime (τA) as a function of injected carrier density (n) shows thattau_{A}^{-1} sim n^{2.1}which is characteristic of an Auger process.     

An experimental study of the influence of boundary conditions on the Gunn effect

The electrical characteristics of long inhomogeneous bulk negative differential mobility (NDM) semiconductor elements (n-GaAs and n-InP) exhibiting various modes of current instabilities at low microwave frequencies have been experimentally observed. Measurements were made of the time-dependent sample current and voltage and of the prethreshold electric-field distribution within the sample. The measurements were made under conditions in which the configuration of the circuit, the properties of the boundary of the NDM element, the sample geometry, the temperature, and the magnetic field were varied. We have obtained excellent agreement between the experimental results and a model in which the sample is assumed to have an assigned value for the electric field at the cathode boundary. Different modes of instability may be accurately modeled by choosing an appropriate value for this field. Three regions of behavior may be identified which correspond to three regions for the cathode boundary field. These regions are 1) cathode boundary field Ecless than the threshold electric field Epfor the onset of NDM; the samples are likely to operate as bulk oscillators, 2)E_{c} > E_{p}but less than the electric field Evcorresponding to the onset of the saturated electron-drift velocity; the samples operate in the Gunn domain mode with a peak-to-valley ratio determined by Ec, and 3)E_{c} > E_{v}the samples yield saturating current versus voltage curves and only weak oscillations are possible.     

Carrier lifetime and threshold of Pb1-xSnxTe lasers in a magnetic field

It is well known that a magnetic field modifies not only the photon energy, but also the threshold current required by semiconductor lasers. However, the extent to which a given field modifies this threshold current depends very strongly upon temperature and on the lifetimes of the carriers in the valence and conduction bands. Theoretical calculations that predict values of threshold current as a function of magnetic field in mixed-crystal Pb1-xSnxTe lasers are presented. The carrier lifetimes in these materials have recently been studied in some detail and turn out to be related to the composition of the material and to its preparation history. Assuming that the carrier Lifetimes are largely determined by the acoustical phonon density or by random distribution of short-range scattering centers, the Kubo formalism can be used to express the individual Landau-level densities of states. From these, the quasi-Fermi levels at any pumping rate can be directly calculated. Fork-conserving transitions, the optical density of states is then determined by a convolution integral method recently reported elsewhere, and the threshold current is computed numerically by the method of Lasher and Stern. Using some of the measured values of carrier mobilities given by Calawa et al., for compositions withx = 0.07andx = 0.20, and using the measured values of Butler and Harman for zero magnetic-field threshold to adjust the gain requirement parameter, threshold currents at 77°K are computed for magnetic field strengths up to 250 kG. Curves are obtained that predict a threshold current for the higher mobility material that decreases by a factor of about 3 with increasing magnetic field out to the vicinity of 10 kG, flattens out, and then slowly increases. For the lower mobility material, an overall higher input current is required; however the curve continues to decrease to 25 kG before flattening out and then beginning to rise.     

有机电致发光器件中复合发光的电场和温度关系

通过分析有机电致发光器件中载流子注入、输运、激子的解离与复合过程，提出了激子解离与复合的理论模型。基于电流连续性方程和Poisson方程，给出了激子复合几率、电流密度及复合效率表达式。研究了外加电压和温度对器件中激子的复合几率及在各种接触条件下外加电压对器件电流和复合效率的影响。结果表明：(1)在一个较宽的注入势垒范围内，复合几率随电场和温度的升高而降低；(2)固定阴极势垒，而阳极势垒由小变大时，器件电流由接触限制向空间电荷限制转变；(3)复合效率随外加电压升高先增加，当电压达一临界值时而陡降，并存在一个最佳的注入势垒值。其计算值与所报道的实验结果相符合。     

Thermal characteristics of deep red (0.77 μm) vertical-cavitysurface-emitting lasers

Spectra have been obtained as a function of current for room temperature operation of deep red (0.77 μm) top-surface-emitting vertical-cavity-surface emitting lasers. From these spectra, the shift from single mode to multimode operation and the temperature rise from below threshold until thermal quenching are determined. By comparison with the wavelength at threshold for vertical cavity lasers with in-plane edge emitting lasers, the mismatch of the Fabry-Perot and gain peak is determined. This mismatch results in the minimum threshold current for the vertical-cavity lasers to occur considerably below room temperature     

Hot electron conduction of PbTe and Pb1−xSnxTe

Experimental and theoretical studies have been made of electron transport and hot electron effects in PbTe and Pb_1?xSn_xTe as a function of alloy composition. Pulsed measurements of the current-voltage characteristics, Hall effect, and the potential distribution were made on epitaxial samples. Current instabilities and high field domain formation were observed. Monte-Carlo calculations of the velocity-field characteristic including the scattering into conduction band W valleys were performed. Reasonable agreement was obtained for the threshold field dependence on alloy composition.     

Negative bias temperature instability mechanisms in p-channel power VDMOSFETs

The negative bias temperature stress induced instabilities of threshold voltage in commercial p-channel power VDMOSFETs have been investigated. The threshold voltage shifts, which are more pronounced at higher voltages and/or temperatures, are caused by the NBT stress induced buildup of both oxide trapped charge and interface traps. However, the observed power low time dependencies of threshold voltage shifts are found to be affected mostly by the oxide trapped charge. The results are analysed in terms of the mechanisms responsible for buildup of oxide charge and interface traps, and the model that explains experimental data is discussed in details.     

High-field properties of n-InP under high pressure

The high electric field properties of n-InP at 300 K have been studied as a function of pressure. Hydrostatic measurements are made in a piston and cylinder apparatus, using a liquid pressure-transmitting medium. The threshold fields (E_T) for transferred electron instabilities range from 7.5 to 8.5 kV/cm at atmospheric pressure. The resistivity of the samples increases with increasing pressure. The most reliable results show that E_T increases slightly with pressure below 40 kbar. This behavior can be explained qualitatively in terms of possible band structure changes. By using known variations of parameters such as effective mass and sub-band energy gaps, detailed theoretical calculations are carried out to fit the data and to determine the correct mode of operation (two- or three-level operation). The results are also compared with analogous experiments on GaAs.     

Temperature dependence of the Gunn threshold in GaAs

Measurement of the temperature dependence of the threshold for transferred electron instabilities in GaAs gives (1/IP(300))×(dIP/dT=?2.4±0.2×10?3 K?1, independent of carrier concentration The threshold field decreases with decreasing T and depends on carrier concentration. Reasonable agreement is obtained with Monte Carlo calculations based on ?-L-X ordering.     

Design impact of positive temperature dependence on drain currentin sub-1-V CMOS VLSIs

In sub-1-V CMOS designs, especially around 0.5-V CMOS designs, on-state drain current of MOSFETs shows positive temperature dependence, being different from the negative temperature dependence in the conventional voltage designs. Combined with low threshold voltage less than 0.2 V, the possibility of temperature instability increases. This paper describes possible temperature instabilities in the low-voltage regime by using circuit simulation environments incorporating temperature change in time and experiments using MOSFETs and the 32-bit adder circuit in quarter-micrometer CMOS technology with a low threshold voltage of 0.25 V     

垂直腔面发射激光器热场特性分析

应用格林函数方法计算了增益波导垂直腔面发射激光器的热传导方程,分析了电流扩展、材料参数和工作条件对温度分布的影响。计算结果表明,电流扩展是影响这种激光器热场特性的主要因素,降低阈值电流是减小温升的有效方法。     

Temperature dependence of the threshold current density in semiconductor lasers (λ = 1050–1070 nm)

The temperature dependences of the threshold current density and threshold concentration in semiconductor lasers based on MOVPE-grown asymmetric separate-confinement heterostructures with an extended waveguide have been studied (wavelengths ?? = 1050?C1070). It is shown that the temperature dependence of the threshold current density in semiconductor lasers becomes markedly stronger at above-room temperatures, which is due to temperature-induced carrier delocalization into the waveguide layers of a laser heterostructure. It was found that the sharp decrease in the thermal stability of the threshold current density with increasing temperature correlates with the coincidence of the Fermi level with the conduction-band bottom of the waveguide layer in the laser heterostructure. It is experimentally demonstrated that an increase in the energy depth and number of quantum wells in the active region of a semiconductor laser improves the thermal stability of the threshold current density. It is demonstrated that the characteristic parameter T ₀ attains a value of 220 K in the temperature range from ?20 to +70°C.     

Consideration on threshold current density of GaInAsP/InP surface emitting junction lasers

The oscillation condition of the GaInAsP/InP surface emitting (SE) junction laser (lambda = 1.3mum) is examined. Theoretical calculations indicate that reflectivity of the mirrors of a Fabry-Perot resonator is necessary to be 95 percent for a reasonably low threshold current density. Then, we have fabricated a new structure for SE laser and compared its threshold current density with the theoretical estimation. In order to maintain the necessary reflectivity without deteriorating the ohmic contact, we adopted a ring electrode where the reflecting mirror is separated from thep-side electrode. The threshold current was reduced down to 35 mA at 77 K which is 70 percent of the early experiment. The threshold current density was estimated to be 5 kA/ cm². The estimated reflectivity was 80-85 percent. The operating temperature has been raised to -21°C (252 K). The temperature dependence of the threshold current near room temperature suggests that room temperature operation of GaInAsP/InP SE lasers is possible by increasing the reflectivity of mirrors and current confinement.     

Impact strain engineering on gate stack quality and reliability

Strain engineering based on either a global approach using high-mobility substrates or the implementation of so-called processing-induced stressors has become common practice for 90 nm and below CMOS technologies. Although the main goal is to improve the performance by increasing the drive current, other electrical parameters such as the threshold voltage, the multiplication current, the low frequency noise and the gate oxide quality in general may be influenced. This paper reviews the impact of different global and local strain engineering techniques on the gate stack quality and its reliability, including hot carrier performance, negative bias temperature instabilities, time dependent dielectric breakdown and radiation hardness. Recent insights will be discussed and the influence of different strain engineering approaches illustrated.     

Specific features of formation and evolution of a longitudinal autosoliton in <Emphasis Type="Italic">p</Emphasis>-InSb in a longitudinal magnetic field

The effect of a longitudinal magnetic field on the formation and behavior of a longitudinal autosoliton in the excited nonequilibrium electron-hole plasma in p-InSb is studied experimentally. It is shown that, in a longitudinal magnetic field, the threshold characteristics of the formation of an autosoliton are reduced and the autosoliton takes on the diamagnetic properties that persist after removal of the magnetic field. In magnetic fields of 9.6 × 10³—4.6 × 10⁴ A m^-1, instabilities of the autosoliton current are excited, with a frequency in the range 2–20 kHz. In this case, the amplitude and frequency of these instabilities depend on the magnetic field. At elevated levels of excitation of the autosoliton and in increased magnetic fields, the instability of the longitudinal-autosoliton current exhibits synergetic properties.     

The influence of light on the properties of NMOS Transistors in laser µ-zoned crystallized silicon layers

Isolated thin Si layers have been grown by laser µ-zone crystallization at high bias temperature. The influence of light on the properties of NMOS silicon gate transistors fabricated in these crystallized silicon layers is investigated. Both leakage current and threshold voltage are light sensitive. The influence of light on the threshold voltage results in a nearly logarithmic dependence of the drain current as a function of the light intensity.     

Controlled stimulated Raman amplification and oscillation in hydrogen gas

The gain of theQ(1)vibrational stokes line of H2has been measured as a function of pressure in a Raman amplifier cell of variable length. The threshold power for stimulated emission of theQ(1)vibrational andS(1)rotational stokes line of H2has been measured in a transverse resonator as a function of pressure. Both geometries give results in good agreement with theory, without invoking any other nonlinear instabilities.     

Modelling of a Cd<Subscript>1−x</Subscript>Zn<Subscript>x</Subscript>Te/ZnTe Single Quantum Well for Laser Diodes

In this paper, the carrier density, temperature and quantum well width effect have been investigated for the optical gain for a Cd_1?xZn_xTe/ZnTe Zinc-blend strained quantum well structure. The device emits laser radiations in green–yellow–orange. Our results showed that the optical gain significantly increases with the increasing of the carrier density. It also increases with the decreasing of the Zn concentration, the well width and the temperature. In addition, the optimal threshold current density values were determined for three alloy compositions as 0.7, 0.8 and 0.9.