Emissionspectroscopic Investigation of Bci3 Discharges

Radiofrequency discharges in neat BCI₃ exhibit 3 broad molecular emissions with intensity maxima at about 305, 350, and 480 nm. The 350 nm system consists of a progression of bands with an average separation of about 130 cm^?1. All three emissions have an identical excitation kinetics in pulse discharges and are, therefore, believed to originate from the same emitter. Arguments are given that the emitter might be electronically excited BCl₂. The dominant process of BCl(A) formation in neat BCl₃ at low r.f. power is shown to be direct electron impact excitation of BCl(X). A transient excess population of BCl(A¹II) in BCl₃/Ar discharges is explained as due to an energy transfer from argon metastables.     

The role of the emitter on the diffusion current inn + p-junctions

On three different samples of crystallinep-siliconn ⁺ p-junctions have been prepared by coating the surface with a phosphorous glass and a subsequent diffusion at 915°C for 30 min. From the measurement of the short circuit current density and the open circuit voltage under high illumination conditions the diffusion current of the solar cells has been determined as a function of the temperature between 77K and 300 K. The contribution of the emitter and the base region to the diffusion current was examined. Under the assumption of Auger recombination governing the hole lifetime in the emitter the narrowing of the mobility bandgap due to the high density of states within the bandgap of the emitter was determined. A shrinkage as high as 0.18 eV was observed in the case of a 0.2 cm sample of lower purity. For high purity 6 cm silicon the reduction of the mobility bandgap was determined as 0.10 eV. A polycrystalline sample exhibits a shrinkage of 0.15 eV. The reduction of the mobility bandgap was found to determine the lower limit of the current losses due to carrier diffusion in our solar cells at current densities around 1×10^–7 Am^–2.     

Of heat capacity at homologous temperatures for metals showing h.c.p. ⇄ b.c.c. transformation

Some interesting aspects of the temperature dependence of the Planck’s functionφ and heat capacities of metals exhibiting the h.c.p. ⇄ b.c.c. transformation have been brought to light by the use of reduced temperature (T*) and Planck’s function (-φ T*). It has been shown that tangents drawn to the -φ T* vsT* plots of these metals at any chosen value ofT* intersect at a point whose coordinates are defined by the slope and intercept ofφ vs entropy plots at any homologous temperature and the selectedT* value. A generalized expression obtained for the temperature dependence ofφ has been used to demonstrate that the heat capacity of these metals may be visualized to have structural and material components.     

Physical processes of current gain in InAs bipolar junction transistors

InAs bipolar junction transistors (BJTs), grown by molecular beam epitaxy, are reported with common emitter current gains (β's) as large as 400. The factors affecting the common emitter current gain have been studied by estimating the magnitudes of the base transport factor (α_T) and emitter injection efficiency (γ). This has been accomplished by studying a sequence of InAs BJTs with varying emitter doping densities, N_E. Minority carrier diffusion length in the base (L_B), α_T, and γ have been extracted from measured electrical characteristics. The results of the study of these InAs BJTs are as follows: L_B≈0.4 μm, α_T≈98% and γ ranges from 92% to nearly 100% depending on N_E. This knowledge of the magnitudes of the injection efficiencies suggests when it would be useful to move from the simple BJT structure to the more advanced heterojunction bipolar transistor (HBT) structure. Lower γ BJTs would be improved, however high-γ BJTs would benefit little, by the use of the widegap emitters of HBTs. The method developed here to estimate γ, α_T and L_B is not specific to InAs BJTs, but should be useful for study of BJTs and HBTs in any material system.     

Enhanced field emission from pulsed laser deposited nanocrystalline ZnO thin films on Re and W

Nanocrystalline ZnO thin films have been deposited on rhenium and tungsten pointed and flat substrates by pulsed laser deposition method. An emission current of 1 nA with an onset voltage of 120 V was observed repeatedly and maximum current density ∼1.3 A/cm² and 9.3 mA/cm² has been drawn from ZnO/Re and ZnO/W pointed emitters at an applied voltage of 12.8 and 14 kV, respectively. In case of planar emitters (ZnO deposited on flat substrates), the onset field required to draw 1 nA emission current is observed to be 0.87 and 1.2 V/μm for ZnO/Re and ZnO/W planar emitters, respectively. The Fowler–Nordheim plots of both the emitters show nonlinear behaviour, typical for a semiconducting field emitter. The field enhancement factor β is estimated to be ∼2.15×10⁵ cm⁻¹ and 2.16×10⁵ cm⁻¹ for pointed and 3.2×10⁴ and 1.74×10⁴ for planar ZnO/Re and ZnO/W emitters, respectively. The high value of β factor suggests that the emission is from the nanometric features of the emitter surface. The emission current–time plots exhibit good stability of emission current over a period of more than three hours. The post field emission surface morphology studies show no significant deterioration of the emitter surface indicating that the ZnO thin film has a very strong adherence to both the substrates and exhibits a remarkable structural stability against high-field-induced mechanical stresses and ion bombardment. The results reveal that PLD offers unprecedented advantages in fabricating the ZnO field emitters for practical applications in field-emission-based electron sources.     

The Rydberg matter laser: excitation, delays and mode effects in the laser cavity medium

Temporal and temperature effects are studied in Rydberg matter (RM) formed from K atoms and N₂ molecules as the active medium in a cavity. The function of this setup as a laser was recently described. Temperature-variation studies show that the photons re-exciting the RM clusters usually have a longer wavelength than the photons emitted in the stimulated emission process in the cavity. The deficit is probably covered by background photons. Very long time constants observed after emitter temperature changes indicate that long-wavelength photon energy is accumulated in the RM clusters. Long-wavelength modes are located farther from the RM emitter. The modal structure can be TEM₀₁ or TEM₀₀, as observed clearly by the spatial structure in rapid pulsing experiments. The in-cavity chopped beam signal is delayed by approximately 50 μs. The initial growth rate of the signal during chopping is temperature dependent. Tailing is also observed by chopping, but rapid pulsing of the beam with a spinning mirror does not show any delay of the start of the lasing. The conclusion is that delays exist in the stimulated emission process. The broad intense band appearing at 11 000 nm is shown to be formed partly by light in the range 3500–5000 nm, probably by standing wave interaction at the grating surface (grating bands).     

Preequilibrium versus thermalized light-charged particle emissions in the40Ar (1100MeV)+24Mg reaction. Dynamical calculations

In an attempt to separate preequilibrium and thermalised emissions of light particles in low impact parameter heavy-ion collisions, the⁴⁰Ar+²⁴Mg reaction has been studied at 27.5 MeV/nucleon. Exclusive measurements have permitted us to examine, in some detail, heavy fragments and charged particles (p, d, t,-particle). The fragments recognized as evaporation residues have been selected and, due to inverse kinematic conditions, the related preequilibrium and statistical emissions of light particles resulting from incomplete fusion reaction appear to be distinguishable to a fair extent. This separation is fully supported by Monte Carlo calculations. Some experimental characteristics of the light particles have been examined and compared to the predictions of dynamical calculations. These calculations, associating a preequilibrium (interpreted as prompt emitted particles) model with a statistical-decay model, follow the evolution of the collision from the point of contact between the projectile and the target to the final evaporation-residue formation on an event by event basis. The predictions of these calculations have been compared to experimental data and satisfactory agreement is achieved for fragment-mass distribution, proton-energy spectra, and proton-angular distribution.     

Effective hydrogenation and surface damage induced by MW-ECR plasma of fine-grained polycrystalline silicon

This work reports the investigations on the effects of the hydrogenation process of thin film polycrystalline n⁺pp⁺ mesa silicon cells using MW-ECR plasma in a conventional PECVD system. Different operating parameters such as MW-ECR power, annealing temperature and the doping level of the emitter region were varied. The n⁺-type emitter regions were obtained by phosphorus diffusion in a conventional furnace using an oxide doping source containing phosphorus (P507 or P509 solutions, from Filmtronics Inc.). The MW hydrogenation was carried out at a sample temperature of 400°C for 60 min. Both types of emitters formed from P507 and P509 showed V _oc of 155 mV and 206 mV, which increased linearly to 305 mV and 331 mV, respectively, after hydrogenation when the MW power varied from 200 to 650 W. However, the sheet resistances of the n⁺ emitter region showed a slight increase depending upon hydrogenation power because of its etching. In a further study, hydrogenated samples were annealed in neutral or forming gas (FG) and we observed interesting results on V _oc in the presence of FG. The FG annealing temperature study revealed a strong dependence of V _oc on MW power, which affected the etching level of emitter and emitter dopant concentration, which controls the diffusion of hydrogen ions during post-hydrogenation step. The results were explained in detail by combining the effects of MW power and dopant level of the emitter.     

Kinetics of unusual photoinduced currents in the solid state of some ferrocene derivatives

Kinetics of change in photoinduced currents (during illumination and after switching off light source) in the solid state of some ferrocene derivatives, namely, ferrocenecarboxylic acid, acetylferrocene, ferrocenecarbaldehyde, hydroxymethyl ferrocene have been studied in dry nitrogen gas atmosphere. Unusual/anomalous photocurrent versus time profiles were observed in some ferrocene derivatives at certain cell temperatures. The kinetics of current changes under photoexcitation and after switching off the light source have been observed to be complicated in nature. Temperature-dependent behavior of the studied kinetics indicates that charge carrier trapping/detrapping and recombination processes are significantly temperature dependent. These processes have an important role in causing the temperature dependent unusual/anomalous photocurrent versus time profiles in the ferrocene derivatives studied.     

Constraining the size of the carrier of the λ5797.1 diffuse interstellar band

The diffuse interstellar band (DIB) at 5797.1 Å is simulated based on three premises: (1) The carrier of the DIB is polar as concluded by T. Oka et al. from the anomalous spectrum toward Herschel 36 (Her 36). (2) The sharp central feature observed by P.J. Sarre's group is the Q-branch of a parallel band of a prolate top. (3) The radiative temperature of the environment is T_r = 2.73 K. A ²Π ← ²Π transition of a linear radical is simulated. Results depend on 10 parameters, with the rotational constant B being the most critical. Comparisons of calculated spectra with observed data constrain B, which in turn constrains the number of heavy atoms to 5 ≤ n ≤ 7. Upper limits based on the Her 36 spectrum and lower limits based on stability against photodissociation are also discussed. The latter is based on the assumption that the DIB molecules are produced top-down from the breakdown of dust rather than bottom-up by chemical reactions. A difficulty with this limit is that J.P. Maier's laboratory has observed many molecules within this size range, some of which have been tested astronomically. Candidates are discussed in light of many prolate tops observed by the P. Thaddeus and M.C. McCarthy microwave group.     

Axially phase-matched parametric four- and six-wave mixing in potassium vapor

Systematic experimental observations of axially phase-matched parametric four- and sixwave mixing processes have been made in potassium vapor pumped on or near the 4S–6S two-photon resonance. An IR up-conversion with a beta barium borate crystal was used for the detection of IR emissions. All the predicted processes have been observed. It is found that the excitation spectra of the emissions for those processes observed in this work are quite different from the excitation spectra of similar processes in sodium vapor. A dye-dependence of some emissions generated by the axially phase-matched parametric six-wave mixing processes has been found by using different dyes in the dye laser. The reason for the dye-dependence is discussed.     

Isotopic ratio of evaporated ions,critical ionization distances,and ionization regions in the process of the field evaporation of molybdenum at high temperatures

A magnetic mass spectrometer with a field ion source has been used to study the steady-state field evaporation of molybdenum at a temperature of 1000–2000 K. Ions of all seven molybdenum isotopes have been observed in the process of evaporation; only low-charge ions Mo⁺² and Mo⁺ have been detected. The critical ionization distances and ionization regions for single- and double-charge Mo ions have been identified based on the measured ion energies and the experimentally determined intensity of the evaporation field. It has been demonstrated that ions are produced in the process of field evaporation of surface atoms at certain distances from the emitter surface in a very narrow spatial region.     

The pure rotational spectra of the two lowest energy conformers of the asymmetric ether C4H9OC2H5

An experimental study has been performed shedding light on the conformational energies of the asymmetric ether n-butyl ethyl ether. Rotational spectroscopy between 7.8 GHz and 16.2 GHz has identified two conformers of n-butyl ethyl ether, C₄H₉OC₂H₅. In these experiments spectra were observed as the target compound participated in an argon expansion from high to low pressure causing molecular rotational temperatures to be below 4 K. For one conformer, 95 pure rotational transitions have been recorded, for the second conformer, 20 pure rotational transitions were recorded. Rotational constants and centrifugal distortion constants are presented for both butyl ethyl ether conformers. The structures of both conformers have been identified by exploring the multi-dimensional molecular potential energy surface using ab initio calculations. From the numerous low energy conformers identified using ab initio methods, the three lowest conformers were pursued at increasingly higher levels of theory, i.e. complete basis set extrapolations, coupled cluster methods, and also taking into consideration zero point vibrational energies. The two conformers observed experimentally are only revealed to be the two lowest energy conformers when high levels of quantum chemical methodologies are employed.     

Thermoluminescence experiments to study lattice defects in aluminosilicates

Summary The thermoluminescent emissions of β-eucryptite and β-spodumene have been recordedvs. temperature and wavelength. Arguments are advanced which allow the observed emission to be ascribed to point defects originated by the exchange of Si⁺⁴ and Al⁺³ ions in (Si, Al)O₄ tetrahedra.     

Optical properties of nonpolar -plane GaN layers

We have studied optical properties of nonpolar a-plane GaN layers grown on r-plane sapphire by metalorganic chemical vapor deposition and hydride vapor phase epitaxy using different nucleation schemes. Several emission bands, which are not typical for c-plane GaN, are observed in the photoluminescence spectra and their excitation-intensity, temperature, and polarization dependencies are examined. In addition, the spatial distribution of the emissions was examined by cathodoluminescence imaging and relations of the different emissions with particular structural features in the layers are revealed. The results are discussed with emphasis on the origin of the emission line and particular recombination mechanisms.     

Multifunctional silicon-based light emitting device in standard complementary metal–oxide–semiconductor technology

A three-terminal silicon-based light emitting device is proposed and fabricated in standard 0.35 μ m complementary metal--oxide--semiconductor technology. This device is capable of versatile working modes: it can emit visible to near infra-red (NIR) light (the spectrum ranges from 500 nm to 1000 nm) in reverse bias avalanche breakdown mode with working voltage between 8.35 V--12 V and emit NIR light (the spectrum ranges from 900 nm to 1300 nm) in the forward injection mode with working voltage below 2 V. An apparent modulation effect on the light intensity from the polysilicon gate is observed in the forward injection mode. Furthermore, when the gate oxide is broken down, NIR light is emitted from the polysilicon/oxide/silicon structure. Optoelectronic characteristics of the device working in different modes are measured and compared. The mechanisms behind these different emissions are explored.     

Comparative investigation of up-conversion luminescence in Tm-doped oxide-chloride germanate and tellurite glasses

Tm³⁺-doped oxide-chloride germanate and tellurite glasses have been synthesized by conventional melting method. Intense up-conversion luminescence emissions were simultaneously observed at room temperature in these glasses. The possible up-conversion mechanisms are discussed and estimated. However, in these Tm³⁺-doped glasses, tellurite glass showed weaker up-conversion emissions than germanate glass, which is inconsistent with the prediction from the difference of maximum phonon energy between tellurite and germanate glasses. In this paper, Raman spectroscopy was employed to investigate the origin of the difference in up-conversion luminescence in the two glasses. Our results confirm that, besides the maximum phonon energy, the phonon density of host glasses is also an important factor in determining the up-conversion efficiency.     

Photoluminescence characteristics of neodymium oxide nanocrystal/titania/ormosil composite sol-gel thin films

Neodymium (III) oxide nanocrystal/titania/organically-modified silane (ormosil) composite thin films have been prepared using a chemical approach consisting of a combination of inverse microemulsion and sol-gel techniques at low temperature. Transmission electron microscopy shows that the neodymium (III) oxide nanoparticles have a needle-like nanocrystal structure. A strong room temperature emission at 1064 nm, corresponding to the ⁴ F _3/2?⁴ I _11/2 transition, has been observed as a function of the heat treatment temperature used for the production of the composite thin films. In addition to this emission, two other main emissions at 890 nm and at 1336 nm have also been observed. In particular, there was a clear shoulder peak at 1145 nm, probably be due to the host matrix, which was observed in all the measured samples and this shoulder peak gave a maximum intensity after heat treatment at 300 °C. Received: 6 September 2000 / Accepted: 15 November 2000 / Published online: 20 June 2001     

UV–visible emission in Tb–Yb codoped tellurite glass on 980-nm excitation

UV–visible upconversion emission from terbium in a Tb–Yb codoped tellurite glass has been observed on 980-nm excitation. The ultraviolet and violet upconversion emissions involve three photons and the blue, green, yellow, and red emissions arise due to two incident photons. The mechanism involved in these emissions is discussed. The effects of doping concentration and of the sample temperature on the upconversion emissions have also been studied. PACS 74.25.Gz; 42.70.Hj; 73.61.Jc; 76.30.Kg; 42.70.Ce     

双极晶体管在强电磁脉冲作用下的损伤效应与机理

针对典型n⁺-p-n-n⁺结构的双极晶体管,从器件内部电场强度、电流密度和温度分布变化的分析出发,研究了在强电磁脉冲(electromagnetic pulse,EMP)作用下其内在损伤过程与机理.研究表明,双极晶体管损伤部位在不同幅度的注入电压作用下是不同的,注入电压幅度较低时,发射区中心下方的集电区附近首先烧毁,而在高幅度注入电压作用下,由于基区-外延层-衬底构成的PIN结构发生击穿,导致靠近发射极一侧的基极边缘处首先发生烧毁.利用数据分析软件,对不同注入电 关键词： 双极晶体管 强电磁脉冲 器件损伤 损伤功率