摘要:

W was found to produce low specific contact resistance (&rgr;c∼8.0×10−5&OHgr; cm2) ohmic contacts ton+‐GaN (n=1.5×1019cm−3) with limited reaction between the metal and semiconductor up to 1000 °C. The formation of the &bgr;–W2N and W–N interfacial phases were deemed responsible for the electrical integrity observed at these annealing temperatures. No Ga out‐diffusion was observed on the surface of thin (500 A˚) W contacts even after 1000 °C, 1 min anneals. Thus, W appears to be a stable contact ton+‐GaN for high temperature applications. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362816

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Oxide layers etched at an angle were fabricated on a 6H‐SiC substrate by varying etching time in diluted hydrofluoric acid, and 6H‐SiC metal–oxide–semiconductor structures with various oxide thicknesses were formed. High‐frequency capacitance–voltage measurements were carried out for determining the change in gate voltages corresponding to the midgap condition as a function of the thickness of the oxide layer, and the depth profile of trapped charge density in the oxide was estimated from the result. It is found that negative charges build up near the 6H‐SiC/SiO2interface, and that positive charges accumulate in the region at 40 nm from the interface. No significant difference is observed in the depth profiles of the trapped charge density between the oxide layers on the carbon and silicon faces. The origin of these trapped charges is discussed in conjunction with the carbon‐related compounds in the oxide layers. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362817

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The current–voltage characteristics of Pd2Si based Schottky diodes on bothn‐ andp‐type silicon measured over a wide temperature range (52–295 K) have been interpreted on the basis of thermionic emission‐diffusion mechanism and the assumption of a Gaussian distribution of barrier heights. It is shown that while the occurrence of a distribution of barrier heights is responsible for the apparent decrease of the zero‐bias barrier height (&fgr;b0) and nonlinearity in the activation energy plot, the voltage dependence of the standard deviation causes the unusual increase of ideality factor (&eegr;) at low temperatures. Also, it is demonstrated that the forward bias shifts the mean barrier height towards the higher side and causes narrowing of the distribution as well. A simple method, involving the use of &fgr;b0vs 1/Tdata, is suggested to gather evidence for the occurrence of a Gaussian distribution of barrier heights and obtain values of mean barrier height and standard deviation. The experimental results correspond to a mean barrier height of 0.80 V, standard deviation 0.05 V, and ideality factor 1.21 for Pd2Si based Schottky barriers onn‐type silicon; these values forp‐type silicon are 0.38 V, 0.03 V, and 1.07, respectively. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362818

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This work presents a comprehensive investigation of carrier transport properties in light‐emitting porous silicon (LEPSi) devices. Models that explain the electrical characteristics and the electroluminescence properties of the LEPSi devices are developed. In metal/LEPSi devices, the forward current density–voltage (J–V) behavior follows a power law relationship (J∼Vm), which indicates a space charge current attributed to the carriers drifting through the high resistivity LEPSi layer. In LEPSipnjunction devices, the forwardJ–Vbehavior follows an exponential relationship (J∼eeV/nkT), which indicates that the diffusion of carriers makes a major contribution to the total current. The temperature dependence of theJ–Vcharacteristics, the frequency dependence of the capacitance–voltage characteristics, and the frequency dependence of the electroluminescence intensity support the models. Analysis of devices fabricated with a LEPSi layer of 80% porosity results in a relative permittivity of ∼3.3, a carrier mobility of ∼10−4cm2/V s, and a free carrier concentration of ∼1013cm−3. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362783

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Two‐photon absorption in GaAs/Ga1−xAlxAs with a realistic band structure and finite band offsets &Dgr;Ec, &Dgr;Evis analyzed theoretically and compared with experiment. This approach allows us to explain the known experimental data and choose the most realistic value for the ratio &Dgr;Ec/&Dgr;Ev. It is shown that for thin quantum wells the number of possible two‐photon optical transitions in the well decreases which strongly affects the polarization dependence of two‐photon absorption in GaAs/Ga1−xAlxAs heterostructures. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362820

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Hole injection into silicon dioxide films from the polycrystalline‐silicon anode or from the anode/oxide interface is demonstrated to unequivocally occur for any case where electrons are present in the oxide conduction band and where the average electric field in the oxide exceeds 5 MV/cm (thick‐film limit) or the voltage drop across the oxide layer is at least 8 V (thin‐film limit). The hole generation is directly shown to be related to the appearance of hot electrons with kinetic energies greater than 5 eV in the oxide conduction band near the anode region. Monte Carlo simulations confirm that the electron energy distribution at the anode is the controlling variable and that hot hole injection occurs mostly over the anode/oxide energy barrier. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362821

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Carrier freezeout in reverse‐biased Hg0.8Cd0.2Te photodiodes has been investigated to determine the relevant acceptor level. At temperatures between 12 and 21 K hole freezeout in thepregion governs the interband tunneling, which dominates the current across the reverse‐biased photodiode. The acceptor level was found to be ∼4 meV in thep‐type Hg0.8Cd0.2Te substrate withNA−ND∼1016cm −3. In comparison with Hall measurements, this new method avoids the uncertainty due to contact caused by surface inversion onp‐Hg0.8Cd0.2Te. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362822

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We investigate modulation‐doped InxGa1−xAs/AlyGa1−yAs quantum wells grown by molecular beam epitaxy with respect to carrier mobility and its dependence on In content, In distribution, populations of electron subbands, and local positions of electron wave functions. We find that the room‐temperature electron mobilities are dominated by the In contents at the maxima of the electron wave functions rather than by the average In contents. At 77 K the mobilities are most strongly influenced by the distance between doping layers and the maxima of the electron wave functions. As a practical result of this study, we present a quantum well structure for high electron mobility transistors with a carrier mobility as high as 8100 cm2/V s at 295 K for an electron density of 2.5×1012cm−2. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362799

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

HighTcsuperconducting materials with nominal compositions of Tl1‐xBix(Sr, Ba)2Ca2Cu3O9(0≤x≤0.5) have been investigated using x‐ray powder diffractometry and electron microscopy. It was found that Tl and Bi cations were in an ordered arrangement in the (Tl, Bi)–O atomic layer. Although the proposed supercell is 4a×4b×4cderived from the basic unit cell of the undoped TlBa2Ca2Cu3O9(Tl‐1223), the basic two‐dimensional superlattice in the (Tl, Bi)–O layer is 2a×4bor 4a×2bwith Bi cations at the center and the corner of the rectangle, giving an ideal and preferred composition with the Tl:Bi ratio of 3:1. Accordingly, the maximum Bi doping for Tl in the solid solution is 25%. The proposed model of the superstructure was supported by computer simulation of electron diffraction patterns. The mechanism of formation of the superstructure is discussed. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362823

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Effects of oxygen partial pressurePO2during low temperature postheat treatments on the superconducting properties of silver‐sheathed Bi2Sr2CaCu2Oytapes were investigated. The critical temperatureTcof the resulting tapes changes systematically withPO2. This variation ofTcis attributed to the change of electronic carrier (hole) concentration by the observation of oxygenK‐edge absorption spectra. The intragranular critical current densityJcis essentially unaffected by the heat treatment, while deterioration in grain connectivity is observed in the specimens treated in reduced‐oxygen atmospheres. The change of anisotropy inJcwith respect to crystallographic orientations is also quite small for the variation ofPO2. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362824

出版商:AIP    

年代:1996

数据来源: AIP