摘要:

We report measurements of the conduction‐band offset in GaAs‐Ga1−xAlxAs multiquantum wells. Admittance spectroscopy is used to measure the activation energy for thermionic emission of electrons over GaAlAs barriers and we discuss the validity of the technique in the presence of a low electric field. We show that the usual approximation in calculating the position of the Fermi level at 0 K can lead to significant error in the determination of the band offset. For an alloy compositionx=0.39, we found a conduction‐band offset of 303 meV.

ISSN:0021-8979    

DOI:10.1063/1.347102

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Noise measurements on unhydrogenated and hydrogenated rf sputtered intrinsic amorphous silicon reported by D’Amico, Fortunato, and Van Vliet [Solid‐State Electron.28, 837 (1985)] have 1/f  and Lorentzian spectra, respectively. Similar noise measurements on glow‐discharge deposited hydrogenated amorphous intrinsic silicon reported by Bathaei and Anderson [Philos. Mag. B55, 87 (1987)] gave a 1/f mspectrum with 0.7<m<1. Even more recently Ley and Arce [Proc. MRS Symposium, San Diego (1989)] have reported random telegraph signals ina‐Si@B:H/a‐Si1−xNx@B:H double barrier structures. The associated noise was a Lorentzian noise spectrum. In this paper the first observation of random telegraph signals in notionally homogeneous heavily doped (p+) glow‐discharged‐deposited amorphous silicon is reported. It was found that the current passing through the sample fluctuates between two easily identifiable levels with the periods of fluctuations separated by a quiescent period. The occurrence of these fluctuations is unpredictable but the current noise spectrum obtained during quiescent periods is Lorentzian, probably indicative of a generation‐recombination process. Noise measurements are not possible at higher biases (>105V/cm) as the current fluctuates chaotically and this is also the prebreakdown regime of the sample.

ISSN:0021-8979    

DOI:10.1063/1.347103

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Photoconductive devices have been fabricated from type IIa diamonds. The sensitivity of these devices is independent of photon energy from 200 to 2200 eV. The dynamic range is 105. The large band gap of the diamond greatly reduces the sensitivity to photons with an energy less than 5.5 eV which is an attractive feature for many applications. The carrier lifetime in the material is 90 ps and the mobility is 1650 cm2/V/s at 106V/m.

ISSN:0021-8979    

DOI:10.1063/1.347104

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Experimental data are presented for the Hall coefficient and the apparent Hall mobility over the temperature range 160–500 K for five samples of molecular‐beam epitaxially grown sulfur‐doped GaSb. The donor concentration of the different samples varied between 3.3×1017and 7.5×1016cm−3, and the native acceptor concentration between 8×1016and 1.2×1016cm−3. The samples show a large spread in the apparent carrier activation energy. A two valley compensated conduction model is presented that shows that the variation in apparent carrier activation energy results from different compensation ratios in the samples. This model also shows that the constant value of the Hall coefficient observed at high temperatures is not due to donor exhaustion but carrier promotion to the lower mobilityL1band. Using constraints provided by secondary ion mass spectrometry and capacitance‐voltage measurements on the samples, as well as growth data, it is shown that a narrow spread of values for the donor binding energy around 60 meV is required to account for the data. It is suggested that this spread is due to the formation of a donor band and to the strongly attractive central cores of the sulphur donors.

ISSN:0021-8979    

DOI:10.1063/1.347098

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Photoinduced‐current‐transient‐spectroscopy and space‐charge‐limited‐current measurements have been performed onn‐type GaS single crystals grown from vapor by iodine chemical transport. Three electron traps located at 0.17, 0.45, and 0.56 eV from the conduction band have been detected, with a thermal capture cross section of 2×10−19, 5×10−14, and 8×10−13cm2, respectively. Moreover, by Hall‐effect measurements, an impurity hopping conduction with an activation energy of 0.12 eV has been evidenced in the range of temperatures between 220 and 320 K.

ISSN:0021-8979    

DOI:10.1063/1.347105

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper reports on the properties of doped and undoped amorphous silicon films deposited by the homogeneous chemical vapor deposition (HOMOCVD) technique. It is shown that good quality films can be grown at reasonable deposition rates of 100–150 A˚/min. It is also shown that in this growth regime, the main precursor is Si2H4, shifting to SiH2at higher H2dilution. The real limit for the growth rate is set by the phenomena of homogeneous and local nucleation. The optical band gap of undoped films deposited at these high growth rates, changes from 2.6 eV for a substrate temperature of 20 °C down to 1.6 eV at 280 °C. Very conductive B‐doped HOMOCVD amorphous silicon films with tunable band gap can be obtained. This is very important for the use of such films for window layers in photovoltaic applications as an alternative to siliconcarbide. At a substrate temperature of 40 °C films were obtained with an optical gap of 2.34 eV and a room‐temperature dark conductivity of 1.6×10−5/&OHgr; cm. Down to a thickness of 100 A˚, no thickness dependence of the dark conductivity has been observed.

ISSN:0021-8979    

DOI:10.1063/1.347106

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Al/p‐CuInSe2Schottky contacts have been fabricated by vacuum‐depositing Al onto Bridgman‐grownp‐CuInSe2single crystals. The barrier heights from the temperature‐dependent forwardI‐Vcharacteristics are significantly less than theC−2‐Vintercepts. This is evidence of the presence of an interfacial layer and surface states in equilibrium withp‐CuInSe2. The barrier height, electron affinity, effective acceptor density, and relative Fermi potential as well as diffusion potential were estimated. The surface‐state density of the minimum order of 1012cm−2 eV−1was obtained for the etched CuInSe2surface. The transverse doping profile was qualitatively determined.

ISSN:0021-8979    

DOI:10.1063/1.347108

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effective bond‐orbital model is used to calculate the subband structures of GaAs/AlGaAs and InGaAs/InP quantum wires of various geometries. The advantages of the effective bond‐orbital model over standard effective‐mass theory are its flexibility to accommodate otherwise awkward geometries, the straightforward manner in which boundaries between materials are treated, and the inclusion in the Hamiltonian of terms inkhigher than quadratic. We focus our attention on the subband structures of epitaxially buried Ga0.47In0.53As/InP quantum wires of triangular cross section with axis in the [011] direction and (111), (11¯1¯), and (100) faces.

ISSN:0021-8979    

DOI:10.1063/1.347109

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Sidegating characteristics of AlGaAs/GaAs heterostructure field‐effect transistors, fabricated on molecular‐beam epitaxially grown layers, were investigated with emphasis on the material properties. A systematic analyses of the epitaxial layers concluded with the identification of the substrate–superlattice‐buffer‐layer interface as the predominant cause of the sidegating effect. Remnant carbon contamination on the GaAs surface was found to produce ap‐type, conducting interfacial region. Controlled oxidation of the carbon on the wafers was accomplished using ultraviolet radiation. This oxide was desorbedinsitubefore epitaxial growth. Secondary‐ion‐mass spectroscopy was employed to estimate the carbon concentration at the substrate–epitaxial‐layer interface for standard cleaned and ultraviolet‐ozone‐treated wafers. The carbon concentration of the interfacial region decreased by two orders of magnitude for the wafers exposed to the ultraviolet radiation. Hall‐effect measurements of standard cleaned and ultraviolet‐ozone‐treated heterostructure wafers, prepared with various buffer layer thicknesses, demonstrated the dominant influence of the interfacialp‐type region on the electronic properties of the material. A comparison of sidegating characteristics for devices fabricated on the two types of wafers is presented and discussed. A dramatic improvement in sidegating was observed for the wafers subjected to the ultraviolet‐ozone cleaning procedure.

ISSN:0021-8979    

DOI:10.1063/1.347110

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The metal‐insulator or metal‐amorphous semiconductor blocking contact is still not well understood. Here, the intimate metal‐insulator and metal‐oxide‐insulator contact are discussed. Further, the steady‐state characteristics of metal‐oxide‐insulator‐metal structures are also discussed. Oxide is an insulator with wider energy band gap (about 50 A˚ thick). A uniform energetic distribution of impurities is considered in addition to impurities at a single energy level inside the surface charge region at the oxide‐insulator interface. Analytical expressions are presented for electrical potential, field, thickness of the depletion region, capacitance, and charge accumulated in the surface charge region. The electrical characteristics are compared with reference to relative densities of two types of impurities. ln Iis proportional to the square root of applied potential if energetically distributed impurities are relatively important. However, distribution of the electrical potential is quite complicated. In general energetically distributed impurities can considerably change the electrical characteristics of these structures.

ISSN:0021-8979    

DOI:10.1063/1.347111

出版商:AIP    

年代:1990

数据来源: AIP