摘要:

The incorporation of the group V components in In1−xGaxAsyP1−y, grown lattice matched to InP by gas source molecular beam epitaxy, has been studied over the entire alloy range, 0≤y≤1, as a function of the group V source composition, the V/III beam flux ratio, and the substrate surface orientation. Several aspects of the group V incorporation are most easily understood in terms of a simple model involving a constant incorporation coefficient and an As ‘‘underpressure’’ condition. An improved description of the results at lower values of the V/III flux ratio is provided by a thermodynamic model based on equilibrium reactions for the formation of the binary constituents, and using the bulk properties of the solid solution. However, the thermodynamic model is quantitatively incorrect for large values of the V/III flux ratio. Furthermore, the results for different surface orientations reveal additional weaknesses in the thermodynamic model and suggest the need to account for the surface bonding configurations in describing the group V incorporation in epitaxial growth. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361241

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The time‐dependent dielectric breakdown (TDDB) characteristics of thin oxide–nitride–oxide (ONO) films containing 4 nm of Si3N4were found to be exclusively determined by statistical thickness fluctuations of the Si3N4layer. A two‐parameter statistical model describes this roughness and explains experimental TDDB data. A simple growth model combined with the statistical model reduces the number of parameters to one. It is consistent with TDDB data and is in quantitative agreement with transmission electron microscopy and x‐ray photoelectron spectroscopy data and is able to explain the origin of the roughness. On an ONO with a 4 nm Si3N4layer and an area of 8 cm2—corresponding to the total storage area of a 256 Mbit dynamic random access memory—the thinnest point in the Si3N4can be expected to be below 10 A˚. So eliminating the Si3N4roughness would bring a drastic improvement in reliability. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361242

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Atomic deposition techniques are investigated for binary semiconductors of the telluride family, namely CdTe and MnTe. An original method for directly determining the CdTe atomic layer epitaxy (ALE) growth rate—in monolayers/cycle—is proposed, consisting in monitoring the reflection high‐energy electron diffraction (RHEED) sublimation intensity oscillations of an ALE grown CdTe layer deposited on a MgTe buffer layer. The ALE CdTe autoregulated growth rate at 0.5 monolayer/cycle (in the substrate temperature domain between 260 and 290 °C) is accounted for on the basis of an atomic model which relies on the alternatingc(2×2) Cd and (2×1) Te surface reconstructions during the ALE cycle. RHEED studies on MnTe atomic deposition, together with x‐ray diffraction and transmission electron microscopy on ALE grown CdTe/MnTe superlattices reveal that all deposited Mn atoms are incorporated so that no autoregulated growth can be achieved. Furthermore, less than one or just one monolayer of Mn must be sent on the surface per ALE cycle to obtain well controlled superlattices with abrupt interfaces. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361243

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We use the high–low capacitance–voltage technique and the conductance–frequency techniques to characterize the SiO2/SiC interface formed by thermal oxidation of the silicon‐face (0001)c‐axis, the (112¯0)a‐axis, and the (11¯00)a‐axis orientations of 6H–SiC. The oxidation rate of thea‐axis orientations is 3–5 times higher than that of the silicon face. Interface state densities on thea‐axis orientations are a factor of 4–10 times higher than the Si‐facec‐axis orientation for bothn‐type andp‐type dopings. Maximum oxide electric breakdown fields are about 10–11 MV/cm for botha‐axis andc‐axis orientations for an oxide thickness of about 60 nm. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361244

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Low‐frequency noise measurements are performed on heavily dopedp‐type GaAs transmission line models. Excess noise exhibits 1/fnoise and generation‐recombination (GR) noise components. A study of the GR components vs device geometry shows the spectral densities due to contact resistances to be negligible. Thus the noise sources due to the volume resistances are predominant, and have to be located in the bulk layer or in the space‐charge region of the devices. These two possibilities concerning the location of the GR noise sources are investigated. For both cases, expressions for the variance and the relaxation time associated to fluctuations in the charge carriers are given. The comparison between the experimental data with the theoretical results shows that the GR noise sources are located in all probability in the space‐charge region. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361245

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have measured the attenuation of picosecond electrical pulses by two‐dimensional electron gases that are monolithically integrated in coplanar transmission lines. By integrating the two‐dimensional electron gas structure into the transmission line, we avoid impedance mismatches that give rise to spurious reflection. The attenuated transients are simulated by an equivalent circuit transmission line model, where the conductivity of the two‐dimensional electron gas underneath the transmission line is taken into account. The measured pulses are fitted with a specific conductivity of the layers corrected with a mode overlap factor, which describes the overlap of the electrical field lines with the two‐dimensional layer. We obtain an overlap factor of 0.8–1.1. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361246

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Ever since their respective appearance in the literature, the Watanable–Actor–Gatos (WAG) and Berz–Kuiken (BK) methods—two voltage‐varying methods for determining the ratio of surface recombination velocity over diffusion coefficient (sT/D) from electron‐beam‐induced current (EBIC) data measured as a function of beam voltage—have coexisted as separate, independent methods. Judged by the frequency of its citations in the literature and endorsements in review articles, the WAG method appears to be the method of choice. In this article it is shown that these two methods have a common origin and that in fact they are identical when the EBIC is linearly related to the effective beam penetration depth. Unifying these methods leads to the development of a more general method, named here as the slope‐extrapolated‐intercepts or SEIs method. To demonstrate its generality, the SEIs method is used to investigate a variety of situations: normal‐ and planar‐collector geometries, Gaussian and point sources, and a wide range of values of material parameters and effective beam penetration depth. It is found that the SEIs method, or the simpler but less general and less accurate BK method, andnotthe WAG method, should be the method of choice to evaluatesT/Dfrom voltage‐varying EBIC data. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361247

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The two existent balance‐equation methods for electron transport, which incorporate Bragg scattering and give rise to bulk negative differential mobility, are further investigated using the Boltzmann transport equation for Bloch electrons. We point out that the ansatz employed in the earlier Bu¨ttiker–Thomas (BT) scheme to relate the average drift velocity and the average momentum, should be modified for a general energy band. Numerical calculation of superlattice miniband conduction shows that the modified BT force‐balance method yields a velocity–field behavior almost equivalent to that predicted by the acceleration‐balance method of Lei, if the appropriate momentum function is used in the calculation of the BT frictional force, such that Bragg scattering is properly taken into account in the process of electron scattering. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361248

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Light‐induced changes in the photo‐, &sgr;ph, and dark, &sgr;d, conductivities of undoped hydrogenated amorphous silicon (a‐Si:H) and amorphous silicon–carbon are investigated as functions of deposition and measurement temperature. Previous work described the temperature dependence of the annealed state &sgr;phand &sgr;dof a series of intrinsica‐Si:H materials deposited over a range of substrate temperatures, 200 °C<Ts<380 °C, and a thermal equilibrium framework for the high temperature behavior of the relationship between concentrations of dangling bond defects (DBs) and free carriers. The annealed‐state results are extended to the light‐degraded state where elevated temperatures ensure equilibration of the free carrier and DB concentrations as suggested by the thermal equilibrium framework. Both &sgr;dand &sgr;phin the light‐degraded‐equilibrium state decrease compared to the annealed state while the ratio, &sgr;d/&sgr;ph, remains unchanged. From this result, relationships between the Fermi level and the ratio of positively and negatively charged DBs are derived in terms of the thermal equilibrium framework equations. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361249

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present photoluminescence (PL), UV absorption, electroluminescence and x‐ray reflectivity studies of self‐assembled multilayer films containing alternate layers of conjugated copolymers, and nonconjugated insulating polymers. We show that the PL emission properties of these organic quantum wells can be ‘‘tuned’’ by a proper choice of the conjugated copolymer and the thickness of the insulating layers. Particularly, some of the self‐assembled ultrathin films containing thin (∼7 A˚) insulating polymeric layers exhibit a blue shift upon decreasing the thickness of the assembly. The PL shift is roughly proportional to 1/d2wheredis the thickness of the assembly, as expected for confined photogenerated electron‐hole pair in an infinite square potential well. In contrast, the PL emission of similar assemblies but containing thick (∼40 A˚) insulating layers is independent of the assembly thickness and exhibit emission in the blue. This may suggest a strong spatial confinement. Light emitting diodes based on self‐assembled multilayer films with improved efficiency and stability and with threshold voltage as low as 2.6 V could be fabricated. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361250

出版商:AIP    

年代:1996

数据来源: AIP