摘要:

Temperature and stress polarity-dependent dielectric breakdown in thin silicon dioxides has been carefully investigated. The experimental data show that the time to breakdown under a constant-current injection has two kinks around 330 and 230 K for 4- and 10-nm-thick oxides under both stress polarities. It has been found that thinner oxides have a stronger temperature dependence (a larger activation energy) even if the field dependence of the activation energy is taken into consideration, and also that, from the gate voltage shift during the constant-current injection, the postbreakdown characteristics strongly depends on the stress polarity for thinner oxides. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122343

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Simulation results depicting physical conditions in a photoconductive semiconductor switch in the pulse charging state, prior to high power switching, are analyzed. Results show that surface conditions and EL2 traps in semi-insulating GaAs influence the conduction process, specifically at high bias. Formation of trap-filled regions renders the device inhomogeneous for stable conduction and premature breakdown occurs, due to a large extent on unstable current filamentation within the device. Unlike insulators, the breakdown of desorbed gas from the surface (surface flashover) does not contribute to premature breakdown. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122344

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Multicrystalline silicon wafers, widely used in commercial photovoltaic cell production, traditionally give much poorer cell performance than monocrystalline wafers (the previously highest performance laboratory devices have solar energy conversion efficiencies of 18.6&percent; and 24.0&percent;, respectively). A substantially improved efficiency for a multicrystalline silicon solar cell of 19.8&percent; is reported together with an incremental improvement in monocrystalline cell efficiency to 24.4&percent;. The improved multicrystalline cell performance results from enshrouding cell surfaces in thermally grown oxide to reduce their detrimental electronic activity and from isotropic etching to form an hexagonally symmetric “honeycomb” surface texture. This texture reduces reflection loss as well as substantially increasing the cell’s effective optical thickness by causing light to be trapped within the cell by total internal reflection. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122345

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The optical band gap in 40 nmGa1−xInxN/GaNsingle heterostructures is investigated in the composition range0<x<0.2by photoreflection spectroscopy (PR) at room temperature and compared with photoluminescence (PL) data. Clear PR oscillations at the GaInN band gap are observed as originating in the large piezoelectric field. Effective band gap bowing parametersbare derived for pseudomorphically stressed GaInN on GaN:b=2.6 eV(PR) andb=3.2 eV(PL in localized states). Using experimental deformation potentials of GaN,b=3.8 eVis extrapolated for the optical band gap in relaxed GaInN material. Previously reported smaller values are discussed. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122346

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Photoluminescence and intraband absorption were investigated inn-doped self-organized InAs andIn0.35Ga0.65Asquantum dots grown on a GaAs substrate. Intraband absorption of the dots is strongly polarized along the growth axis in the mid infrared spectral range. The absorption is maximum at around 120 meV for InAs dots and at 130 meV forIn0.35Ga0.65Asdots. The experimental results on InAs dots are in agreement with published theoretical calculations. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122347

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Raman spectra fromp-type GaN have been systematically studied in the hole density range of5×1016–1×1018 cm−3.Contrary to the case ofn-type samples, spectral profiles of the LO-phonon-plasmon coupled mode inp-type show no remarkable change with the hole density. Thus, precise evaluation of electrical transport parameters such as carrier density and mobility from the coupled mode profile is difficult. However, a continuum band has been observed in the low-frequency range of the spectra, becoming intense with the increase of the hole density. This band has been attributed to the inter-valence-band transition of holes, and the intensity can be used as a good measure of the hole density. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122348

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Thermal generation rate in quantum dots (QD) can be significantly smaller than in quantum wells, rendering a much improved signal to noise ratio. QDs infrared photodetectors were implemented, composed of ten layers of self-assembled InAs dots grown on GaAs substrate. Low temperature spectral response shows two peaks at low bias, and three at a high one, polarized differently. The electronic level structure is determined, based on polarization, bias, and temperature dependence of the transitions. Although absorbance was not observed, a photoconductive signal was recorded. This may be attributed to a large photoconductive gain due to a relatively long lifetime, which indicates, in turn, a reduced generation rate. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122349

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The emission mechanisms of strainedInxGa1−xNquantum wells (QWs) were shown to vary depending on the well thickness,L, andx. The absorption edge was modulated by the quantum confined Stark effect and quantum confined Franz-Keldysh effect (QCFK) for the wells, in which, for the first approximation, the product of the piezoelectric field,FPZ,andLexceed the valence band discontinuity,&Dgr;EV.In this case, holes are confined in the triangular potential well formed at one side of the well producing the apparent Stokes-like shift. Under the condition thatFPZ×Lexceeds the conduction band discontinuity&Dgr;EC,the electron-hole pair is confined at opposite sides of the well. The QCFK further modulated the emission energy for the wells withLgreater than the three dimensional free exciton Bohr radiusaB.On the other hand, effective in-plane localization of carriers in quantum disk size potential minima, which are produced by nonrandom alloy compositional fluctuation enhanced by the large bowing parameter andFPZ,produces a confined electron-hole pair whose wave functions are still overlapped (quantized excitons) provided thatL<aB.©1998 American Institute of Physics.&hthinsp;

ISSN:0003-6951    

DOI:10.1063/1.122350

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In this letter, we report on the investigation of Si/Pt Ohmic contacts top-type 4H–SiC. The contacts were formed by a vacuum annealing method at 1100&hthinsp;°C for 3 min, which resulted in specific contact resistivities in the low10−4 &OHgr;&hthinsp;cm2range. Auger analysis has shown that, at this anneal temperature, there was a uniform intermixing of the Si and Pt, migration of Pt into the SiC, and out-diffusion of C into the metallization layers. Overlayers of Au or Ni/Au on Si/Pt had the effect of decreasing the specific contact resistance and improving the surface morphology of the annealed contacts. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122351

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Using a low-temperature microphotoluminescence method, we have investigated the optical properties of oval defects in a GaAs layer grown by molecular beam epitaxy. The photoluminescence (PL) spectra of oval defects exhibited new distinct peaks, which had a narrow width (0.5 meV) and a strong intensity comparable to the exciton luminescence from a defect-free region of the epilayer. The excitation-power dependence and our PL image measurements suggest that the peaks are due to the recombination of excitons bound to the defects. The PL image of the free-exciton luminescence clearly revealed the features of a pair of asymmetric oval defects, each of which had a pyramidal structure consisting of stacking fault planes. The clear features indicate effective carrier confinement within the pyramid, where the stacking fault planes functioned as a potential barrier. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122352

出版商:AIP    

年代:1998

数据来源: AIP