摘要:

Thin films of silver salt of alginic acid, a typical high molecular carboxylic acid in nature, were photolyzed by 253.7 nm light. On irradiating with a 15‐W sterilization lamp in air at relative humidity of more than 70%, the silver alginate films first became yellow‐brown colored due to formation of photolytic colloidal silver particles. When irradiation was continued, the irradiated surface of the films finally changed into clear silver mirror. The morphology of these films was observed by means of a high‐resolution scanning electron microscope. Colloidal silver particles (10–50 nm diam) formed by a short‐time irradiation were sparsely distributed at the film surface. As a result of prolonged irradiation for ∼180 min, film surface was covered with aggregated colloidal silver. The x‐ray diffraction study of the irradiated films revealed sharp diffraction lines, indicating that the colloidal silver was in a highly crystalline state. A preliminary observation of a microtomed cross section of the film showed that colloidal silver particles had a tendency to precipitate at the irradiated side of the film. These observations were consistent with more than a 108‐fold decrease of the sheet resistance and change in transmittance spectra of the films caused by photolysis. It has been proposed that silver atoms from the silver alginate migrate and coalesce to yield the colloidal silver. The colloidal silver particles further diffuse in the film and aggregate themselves at the irradiated surface, giving rise to silver metal films.

ISSN:0021-8979    

DOI:10.1063/1.346731

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effects of in‐plane lattice mismatch have been studied for Ga0.92In0.08As(p+)/GaAs(n)/GaAs(n+) diodes. Different in‐plane mismatch at thep–njunction was introduced by a variation of the GaInAs layer thickness (h=0.1, 0.25, 0.5, and 1 &mgr;m). Capacitance‐voltage (C‐V) measurements with different frequencies show a higher‐frequency dispersion for a greater lattice‐mismatched sample. From the frequency dependence of theC‐Vcurve, single‐level charged interface‐state density (Ns) was estimated using the effective parallel capacitance and conductance components. The average charged interface densityNsswas also estimated using Voltage‐intercept (Vint) method.Nssshows a linear dependence on the in‐plane mismatch. The charged interface state density is approximately 2.7 &Dgr;a∥/a30for partially lattice‐relaxed heterojunctions. For the 1 &mgr;m sample, the forwardI‐Vcharacteristic shows quasi‐Fermi level pinning effect. Admittance spectroscopy measurement gives an equilibrium Fermi energy at aboutEv+0.36 eV with hole capture cross sectioncp=2.7×10−15cm2for the 1 &mgr;m sample and atEv+0.21 eV andcp=2.4×10−16cm2for the 0.5 &mgr;m sample.

ISSN:0021-8979    

DOI:10.1063/1.346699

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Detailed 77‐K and temperature‐dependent photoluminescence (PL) investigations of heterojunction bipolar transistor (HBT) structures grown by low‐pressure metalorganic vapor‐phase epitaxy are presented. HBT layer sequences with GaAs base and with AlxGa1−xAs base graded in the Al content are investigated. Different peaks belonging to GaAs and AlGaAs layers within the HBT structure are identified. It is shown that the PL spectrum is not only the superposition of single‐layer signals, but also provides additional information about the incorporation of the base dopant Mg into the emitter and collector regions of the HBT during epitaxial growth. The presence of Mg in the collector leads to a signal absent in PL of single‐layer GaAs doped merely with Si. It is interpreted as a free‐to‐bound Mg acceptor transition, and its intensity scales with the amount of diffused Mg. Two additional AlGaAs PL peaks besides that from the usual band‐gap recombination are found to be correlated with Mg in the emitter. Their signal strength is dependent on the Mg concentration level. It will be shown that careful evaluation of the HBT spectra can help to decide whether a certain structure under investigation meets the requirements for further device processing.

ISSN:0021-8979    

DOI:10.1063/1.346700

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Abrupt Mg doping profiles have been realized innpnGaAs/GaAlAs heterojunction bipolar transistor (HBT) structures with compositional grading in the base region. The layers were grown by metalorganic vapor‐phase epitaxy (MOVPE). Acceptor concentrations in the base are 1×1019cm−3. Mg is also incorporated in the emitter and cap layers due to the Mg memory effect, and in the collector layer due to dopant diffusion. The incorporation of Mg is found to depend on the Si‐donor concentration in these layers. Annealing experiments at 840 °C show only little broadening of the Mg doping profile. High‐temperature process steps will consequently not change the Mg concentration significantly. We will demonstrate that neither the Mg memory effect nor Mg dopant diffusion limits the use of Mg for MOVPE‐grown HBT layer sequences.

ISSN:0021-8979    

DOI:10.1063/1.346701

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An iterative method for solving the discretized steady‐state semiconductor device equations is presented. This method uses Gummel’s block iteration technique to decouple the nonlinear Poisson and electron‐hole current continuity equations. However, the main feature of this method is that it takes advantage of the diagonal nonlinearity of the discretized equations, and solves each equation iteratively by using the nonlinear Jacobi method. Using the fact that the diagonal nonlinearities are monotonically increasing functions, it is shown that this method has two important advantages. First, it has global convergence, i.e., convergence is guaranteed for any initial guess. Second, the solution of simultaneous algebraic equations is avoided by updating the value of the electrostatic and quasi‐Fermi potentials at each mesh point by means of explicit formulae. This allows the implementation of this method on computers with small random access memories, such as personal computers, and also makes it very attractive to use on parallel processor machines. Furthermore, for serial computations, this method is generalized to the faster nonlinear successive overrelaxation method which has global convergence as well. The iterative solution of the nonlinear Poisson equation is formulated with energy‐ and position‐dependent interface traps. It is shown that the iterative method is globally convergent for arbitrary distributions of interface traps. This is an important step in analyzing hot‐electron effects in metal‐oxide‐silicon field‐effect transistors (MOSFETs). Various numerical results on two‐ and three‐dimensional MOSFET geometries are presented as well.

ISSN:0021-8979    

DOI:10.1063/1.346702

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The electrical characteristics of the amorphous silicon (a‐Si:H) field‐effect transistors have been analyzed theoretically. It is found that if no interface states exist at the SiO2anda‐Si:H interface, the transistor with undoped channel gives the best subthreshold swing and on/off current ratio. However, the existence of the interface states shifts the threshold voltage and reduces the transconductance of the transistor. It is found from numerical analysis that the problem caused by the interface states could be compensated for by doping the channel slightly with phosphorus. The physical reason for the improved performance is discussed in detail.

ISSN:0021-8979    

DOI:10.1063/1.346703

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

New types ofa‐Si:Hp‐i‐ndiodes, capable of sustaining high reverse electric fields up to 6×105V/cm with very low leakage currents, have been designed specifically for charged particle detection. Because of the low hole mobility and lifetime in this type of material, very high applied fields are required to collect a large fraction of the charge carriers generated by an ionizing particle. Since the leakage current is shown to be essentially due to electron tunneling through thep‐doped layer, the new design includes a thickerplayer (300 nm) at the expense of an increased surface leakage current. An appropriate etching of the top doped layer around the electrode is then required to eliminate such currents. A model, taking into account the doped layer conductivities, is presented to roughly compare the reverse current‐voltage characteristics of the samples before and after etching.

ISSN:0021-8979    

DOI:10.1063/1.346704

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Recently, the performance of both solar cells and photovoltaic systems have been considerably improved by the use of a prismatic cover applied to cell surfaces. This cover steers light away from the metal contact fingers on the top surface of the cell that would normally obscure the cell surface. Although the experimental advantages of this approach are now well documented, there is no published analytical treatment of these covers. This paper investigates their design for both concentrating and nonconcentrating application and clarifies the potential and limitations of the approach.

ISSN:0021-8979    

DOI:10.1063/1.346705

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report on the effect of furnace annealing on 60‐A˚‐wide InxGa1−xAs/GaAs single quantum wells (SQWs) in the range of indium composition 0.1≤x≤0.5. Excitonic energy shifts of up to 120 meV were observed after annealing of the samples at 825 °C for 30 min. The fact that these energy shifts were strongly dependent of the indium composition in the well material was consistent with enhancement on the indium diffusion out of the wells associated with the presence of dislocations. The most dramatic changes, as a result of annealing, manifested by strain recovery were observed from the SQW withx=0.3 which as‐grown had a low dislocation density (quantum well thickness slightly exceeding the critical layer thickness for formation of dislocations).

ISSN:0021-8979    

DOI:10.1063/1.346680

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A versatile pulsed laser deposition chamber was employed for fabricating metal buffer layers and superconducting YBaCuO thin films on metallic substrates. Ag buffer layers were found to improve the resistive transition behavior for superconducting films on Pt and stainless steel. As‐deposited YBaCuO films withTc(R=0) at 84 K were produced on stainless steel usinginsitulaser‐deposited Ag buffer layers. The critical current density was measured to be approximately 103A/cm2at 67 K.

ISSN:0021-8979    

DOI:10.1063/1.346681

出版商:AIP    

年代:1990

数据来源: AIP