摘要:

AlxGa1−xAs–GaAs structures with thin (400–1000 A˚) Cr‐doped or unintentionally doped AlxGa1−xAs layers (0.3≤x≤1) were grown onn+GaAs substrate by molecular‐beam epitaxy. The AlxGa1−xAs–GaAs interface and the insulating properties of thin AlxGa1−xAs layers at 300 K have been studied by capacitance–voltage and current–voltage measurements, respectively. An AlxGa1−xAs–GaAs interface state density in the lower 109eV−1cm−2range was obtained. The insulating properties of thin AlxGa1−xAs layers were found to be controlled by AlxGa1−xAs–GaAs interface band offsets (&Dgr;Eo,&Dgr;Ev) and metal–AlxGa1−xAs barrier height &Fgr;Bnin accumulation and deep depletion, respectively, rather than by AlxGa1−xAs bulk properties such as specific bulk resistivity. Furthermore, required electrical properties of insulating layers employed in metal–insulator–semiconductor structures are discussed using a self‐consistent heterostructure model based on Poisson’s equation and current continuity equations. Finally, a fundamental equation for the formation of inversion channels has been derived. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360416

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Variational and diffusion quantum Monte Carlo simulations of excitons in the type‐II semiconductor quantum well system In1−xGaxAs/GaSb1−yAsyare performed for a wide range of composition (0,0)≤(x,y)≤(0.62,0.64) and well width 25 A˚ ≤L≤200 A˚. The exciton binding energy is found to increase with the decrease of the layer thickness and with the increase of the composition. The calculated results suggest that a novel semiconductor–excitonic insulator (Bose condensate)–semimetal transition should be observable in this system. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360417

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Zirconium titanate (ZrTiO4) thin films (200–260 nm) onp‐type (100) Si substrates were prepared using radio‐frequency sputter deposition at room temperature in atmosphere of various O2/Ar mixing ratio (from 0/100 to 20/80). All films exhibited a (020) preferred orientation and small grain size with increasing O2/Ar ratio, as shown by x‐ray diffraction. The variations of dielectric constant, fixed oxide charge, and interface trapped charge with O2/Ar ratio are studied with an Al/ZrTiO4/Si structure. The refractive index and dielectric constant varied in ranges 2.34–2.26 and 20–16 for the as‐deposited films. Within the range investigated, crystallinity appears to have a stronger influence on the densities of charge‐trapping centers in the films than oxygen stoichiometry, and the latter may determine the leakage current density. A remarkable two orders of magnitude decrease in leakage current to 5.6×10−9A/cm2at 0.1 MV/cm and an increase in breakdown field beyond 1.2 MV/cm are observed in the film deposited without oxygen after a 400 °C annealing in air for 1 h. The current transport in ZrTiO4film is dominated by the Poole–Frenkel mechanism. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360418

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present the results of detailed electrical measurements on diamond films grown by hot‐filament chemical‐vapor deposition. Two different mixtures of reaction species, hydrogen/methane and hydrogen/acetone, were utilized to grow diamond films. The latter is useful for introducing dopants during growth in a relatively safe manner. For the diamond films grown using hydrogen and methane, a high‐temperature anneal increased the resistivity of the films by seven orders of magnitude to about 1012&OHgr; cm while theI–Vcharacteristics retained the same qualitative shape. Further annealing was found to change theI–Vcharacteristics of the film itself, not the contacts. Spatial variation of the electrical characteristics is also reported. In addition, for the diamond films grown using the hydrogen and acetone, a variety of different results was obtained. Electrical measurements and Raman spectroscopy suggest that some areas of these films were high‐resistivity diamond while other areas may contain nondiamond carbon at grain boundaries. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360419

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present quantum transport anomalies in the theoretical conductance of various semiconductor nanostructures. We first investigate a quantum channel with a chain of quantum boxes connected by slits, called a superlattice structure, and study the miniband and minigap effects associated with resonances and anti‐resonances in the conductance. We also report studies of electron transport in a quantum wire containing series or parallel slits and a detector slit. In these systems, strong conductance oscillations due to quantum interference effects are predicted as a detector slit is moved across the wire. In the case of a single and multi‐series slits, we attribute these effects to multiple reflections of the phase‐coherent electron along the quantum wire. The transmission coefficients and electronic phase shifts are examined, which provide insights into the origins of these conductance oscillations. In the case of multi‐parallel slits, peaks with two‐ (four‐) fold splitting in the conductance are exhibited due to the quantum branch interference between the two (four) alternative electron paths. We also study the conductance of a quantum structure containing an artificially produced impurity. It is shown that the conductance modulations are strong when the impurity is scanned across the channel. We explain these oscillatory features of the conductance by a simple optical interference model and a simple adiabatic model. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360771

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A system of nanometer sized cobalt clusters surrounded by dielectric shells has been investigated by electrical dc conductivity measurements. The cobalt clusters have a diameter of 36 A˚ and are surrounded by an approximately 12‐A˚‐thick layer of tetra‐octyl‐ammonium bromide surfactant molecules and poly(phenyl‐p‐phenylenevinylene). The conductivity &sgr; shows a temperature dependence ln(&sgr;)∝(T0/T)1/2in the range 100<T<240 K. AtT≳240 K, the temperature dependence of the conductivity demonstrates some peculiarities. Differential scanning analysis suggests that at 240<T<350 K phase transitions of the composite material take place. The observed temperature dependence of the conductivity &sgr; forT<240 K is typical for hopping conduction in granular metallic systems. A theoretical analysis shows that the data are consistent with a hopping model in which the separation between grains is a random variable uncorrelated with the activation energy. The observed nonlinear dependence of the conductivity on the electric fieldFis interpreted in the framework of the concept of the effective temperature, which suggests that the influence ofTandFon &sgr; can be parameterized by a single quantityTeff(T,F). Comparison between the theoretical results and experimental data provides a suitable expression forTeff(T,F). ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360420

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The linearity between photoluminescence characteristics and incident laser power is discussed on the basis of an electric field distortion induced by photoexcitation in a GaAs/GaAlAs multi‐quantum well structure. Peak intensities and wavelengths at half maxima of PL spectra have been analyzed quantitatively for different incident laser powers. The relation is nonlinear in the case of the cap layer where two contacts are both Al Schottky metals although linear in the case of an Al Schottky metal and a AuGe ohmic alloy. The difference can be explained theoretically considering an electric field distortion induced by the accumulation of photogenerated holes in the GaAs cap layer. The nonlinear relations are due to the large accumulation rate of holes in the cap layer. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360421

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The performance characteristics of type‐II InAs/InxGa1−xSb superlattices for long and very long‐wave infrared detection are discussed. This system promises benefits in this wavelength range over conventional technology based on Hg1−xCdxTe, in part because of suppressed band‐to‐band Auger recombination rates which lead to improved values of detectivity. The formalism for calculating Auger rates in superlattices is developed and the physical origin of Auger suppression in these systems is discussed. AccurateK⋅pband structures are used to obtain radiative, electron–electron, hole–hole, and band‐to‐band Auger rules, as well as shallow trap level assisted Auger recombination rates for photodiodes. Theoretical limits for high temperature operation of ideal photovoltaic detectors are presented and compared with HgCdTe. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360422

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The effects of purification by reactive sublimation technique and bromine doping on the Fermi level and the photovoltaic properties ofn‐type perylene pigment films were investigated. Photovoltage arisen from the Schottky junction betweenn‐type perylene pigment film and Au increased significantly by repeating the train sublimation under methylamine gas atmosphere. This phenomenon was revealed to be due to the negative shift of the Fermi level resulting from the effective removal of unknown but specific impurity acting as an acceptor by reactive sublimation. On the other hand, by bromine doping, Fermi level of the pigment film shifted largely to a positive direction and reached the nearby valence band, while the direction of photocurrent flow arising from the Schottky junction with Au was reversed. This result is a clear demonstration of alternating the type of conduction fromntype toptype. This means that thepncontrol of organic semiconductors is possible. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360423

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Addition of germanium to the Se–Te alloy causes structural changes which modify the band structure and hence the electrical properties of the Se–Te alloy. In the present work, electrical, optical, and structural properties of Se–Te–Ge have been studied. The activation energies calculated from the dc resistivity measurements were changed from 0.15 to 0.39 eV with the change of germanium and thickness of the film. Refractive indexn, extinction coefficientk, and dielectric constant &egr; of Se–Te–Ge alloy thin films showed significant change with light energy. Crystallization of the sample is achieved at 573 K. The amorphous Se–Te–Ge system is useful as a good photovoltaic material. The dc conductivity measurements were carried out from 294 to 555 K. The effect of heat treatment on optical absorption was investigated. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360424

出版商:AIP    

年代:1995

数据来源: AIP