摘要:

Schottky contacts were formed on Cl‐dopedN‐type lattice matching ZnS0.07Se0.93epilayers grown on (100)N‐GaAs substrates by molecular beam epitaxy for metals with different work functions, Yb, Al, Cr, Cu, Au, and Pd. Temperature‐dependent current‐voltage and capacitance‐voltage (C‐V) measurements show a clear relation between Schottky barrier height and metal work function which cannot be predicted by the linear Schottky contact theory, &Fgr;SB=&Fgr;M−&khgr;. The pinning effect is believed to exist at the metal‐semiconductor interface with a wide range of Fermi level pinning positions. Thermionic emission dominates the current transport mechanism and the current is limited by the ZnSSe/GaAs heterojunction under a relatively high positive bias. A symmetriclikeC‐Vcharacteristic is explained by the Schottky barrier‐heterojunction model and a fairly constant heterojunction barrier height, &Fgr;HJ, is obtained for Schottky diodes using different metals. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358645

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoconductive semiconductor switches (PCSS) have high‐voltage hold‐off (many to tens of kilovolts) and fast current rise times (<1 ns). However, lock‐on, nonuniformities in the electric field, and filamentary current flow across the device when switching at high fields (∼10 kV/cm) have been reported. These observations raise concerns about the scaling of PCSS to high currents (tens of kiloamperes). To investigate these issues a two‐dimensional time dependent computer model of a GaAs PCSS with Si and Cu doping has been developed. The model solves the continuity equations, the bulk energy equation, Poisson’s equation for the electric field, and a circuit equation for external currents. Physical effects in the model include band‐to‐band impact ionization, trap impact ionization, photoionization, and negative differential resistance. Computed characteristics of GaAs(Si:Cu) switches will be reported. Experimentally observed electric‐field distributions are explained. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358646

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have fabricated metal‐insulator‐semiconductor field‐effect transistors (MISFETs), with thin films of polycrystalline poly(p‐phenylene vinylene) (PPV) as the semiconducting layer and report here the successful operation of a PPV MISFET based on thep‐type doping of the polymer layer by ion implantation of iodine. The measured field‐effect mobility of the charge carriers in this ion‐ implanted PPV is in the range of 10−7to 10−8cm2/V s. These values are in the same range as those obtained from a PPV MISFET in which the PPV was doped from the gas phase. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358647

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Magnetic refrigeration, an emerging new technology for cooling and gas liquefaction, needs magnetic materials with specific thermomagnetic behavior. Depending on the thermodynamic cycle selected, the isothermal magnetic entropy change or the adiabatic temperature change upon field application needs to be a preselected function of temperature. To obtain these properties, most designers rely on calorimetry, an expensive and time consuming technique. The present article describes that, classical magnetic measurements, when evaluated within the framework of the Landau theory for the second order phase transition or the thermodynamics in magnetic fields, are able to provide the preliminary information needed for the design of magnetic refrigerators. After reviewing the theory, experimental results on ferromagnetic gadolinium (Gd) and helimagnetic dysprosium (Dy) are analyzed and compared to direct experimental results as well as to those obtained using the molecular field model. The results demonstrate the reproducibility of entropy calculations and the good agreement between the experimental and the calculated specific heat anomalies. While the molecular field theory which assumes simple ferromagnetic order clearly fails for helimagnetic dysprosium, an analysis of the experimental data based on the Landau theory gives reliable results. Besides, the field and temperature dependencies of the isothermal magnetic entropy change allows one to characterize the magnetic structure (nature of the magnetic order) of the sample. Furthermore, magnetic measurements define the useful field range and provide information on transitions that influence the thermal behavior and magnetic losses. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358648

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have experimentally and analytically studied the statistically inhomogeneous distributed dopant atoms in silicon metal‐oxide‐semiconductor field‐effect transistors (MOSFETs) with very small dimensions, by investigating the threshold voltage characteristics. By interchanging the source and the drain terminals of an individual MOSFET in an 8192 MOSFET array within an area of less than 0.7 mm2, it was found that the asymmetry of the threshold voltageVthof a MOSFET is observed only at high drain bias, and continues to increase with increasing the drain bias and scaling the channel length down. These results can be quantitatively explained by our analytical model in which the dopant atoms are inhomogeneously distributed along the channel and statistically fluctuated in the local region of the channel among 8192 MOSFETs. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358581

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A method has been proposed for the determination of localized‐state distributions in amorphous semiconductors from transient photoconductivity using Laplace transforms [H. Naito, J. Ding, and M. Okuda, Appl. Phys. Lett.64, 1830 (1994)]. The method is applicable to both pre‐ and postrecombination regimes of transient photoconductivity, and to amorphous semiconductors exhibiting either nondispersive or dispersive transport. To simplify the analysis of the method, a new approach with the same advantages of the method is presented. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358582

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ion‐beam mixing in AlxGa1−xAs and InP matrices was measured as a function of irradiation temperature using 1 MeV Kr ion irradiation. For these III–V compound semiconductors, the mixing increased with temperature up to a critical temperatureTcat which point it precipitously dropped.Tcwas identified as the amorphous‐to‐crystalline transition temperature in these materials under 1 MeV Kr irradiation. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358583

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The optical properties of a series of In then Ag sequentially implanted silica samples are examined as a function of the relative concentrations of implanted In and Ag. The doses used were in ratios, In to Ag, of 9:3, 6:6, and 3:9. Energy of implantation was 320 keV for the In and 305 keV for the Ag. Nominal total doses as determined by current integration for the three samples were 12×1016(In+Ag) ions/cm2. The depth profile of the implanted ions and optical absorption were found to be a function of the relative doses and to differ significantly from samples implanted separately with either In or Ag. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358584

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In this communication we report the results of a systematic study on the formation of chemically etched porous silicon. Samples have been fabricated in HF/HNO3‐based solutions for various etching times, using different molar concentrations of nitric acid. The growth of the porous layer has been studied by correlating film porosity and thickness to the etching time. Pore formation is shown to be more related to the surface morphology than to the etch characteristics. Preliminary results on photoluminescence measurements show that substrate morphology also play a major role in the luminescent behavior of chemically etched porous silicon. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358585

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a systematic study of the compositional dependence of AlAsySb1−ylayers, grown by molecular beam epitaxy, on the ratio of As to Sb fluxes and on the substrate temperature. The initial results clearly demonstrate that variations in the composition can be observed by changing the above‐mentioned parameters. The emphasis of this communication is on understanding the qualitative trends of these dependencies. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.358586

出版商:AIP    

年代:1995

数据来源: AIP