Journal of Applied Physics
1089-7550
0021-8979
Mỹ
Cơ quản chủ quản: AIP PUBLISHING , American Institute of Physics
Lĩnh vực:
Physics and Astronomy (miscellaneous)
Các bài báo tiêu biểu
Polymorphic transitions in single crystals: A new molecular dynamics method A new Lagrangian formulation is introduced. It can be used to make molecular dynamics (MD) calculations on systems under the most general, externally applied, conditions of stress. In this formulation the MD cell shape and size can change according to dynamical equations given by this Lagrangian. This new MD technique is well suited to the study of structural transformations in solids under external stress and at finite temperature. As an example of the use of this technique we show how a single crystal of Ni behaves under uniform uniaxial compressive and tensile loads. This work confirms some of the results of static (i.e., zero temperature) calculations reported in the literature. We also show that some results regarding the stress-strain relation obtained by static calculations are invalid at finite temperature. We find that, under compressive loading, our model of Ni shows a bifurcation in its stress-strain relation; this bifurcation provides a link in configuration space between cubic and hexagonal close packing. It is suggested that such a transformation could perhaps be observed experimentally under extreme conditions of shock.
Tập 52 Số 12 - Trang 7182-7190 - 1981
Detailed Balance Limit of Efficiency of <i>p-n</i> Junction Solar Cells In order to find an upper theoretical limit for the efficiency of p-n junction solar energy converters, a limiting efficiency, called the detailed balance limit of efficiency, has been calculated for an ideal case in which the only recombination mechanism of hole-electron pairs is radiative as required by the principle of detailed balance. The efficiency is also calculated for the case in which radiative recombination is only a fixed fraction fc of the total recombination, the rest being nonradiative. Efficiencies at the matched loads have been calculated with band gap and fc as parameters, the sun and cell being assumed to be blackbodies with temperatures of 6000°K and 300°K, respectively. The maximum efficiency is found to be 30% for an energy gap of 1.1 ev and fc = 1. Actual junctions do not obey the predicted current-voltage relationship, and reasons for the difference and its relevance to efficiency are discussed.
Tập 32 Số 3 - Trang 510-519 - 1961
A comprehensive review of ZnO materials and devices The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. Lett. 16, 439 (1970)]. In terms of devices, Au Schottky barriers in 1965 by Mead [Phys. Lett. 18, 218 (1965)], demonstration of light-emitting diodes (1967) by Drapak [Semiconductors 2, 624 (1968)], in which Cu2O was used as the p-type material, metal-insulator-semiconductor structures (1974) by Minami et al. [Jpn. J. Appl. Phys. 13, 1475 (1974)], ZnO∕ZnSe n-p junctions (1975) by Tsurkan et al. [Semiconductors 6, 1183 (1975)], and Al∕Au Ohmic contacts by Brillson [J. Vac. Sci. Technol. 15, 1378 (1978)] were attained. The main obstacle to the development of ZnO has been the lack of reproducible and low-resistivity p-type ZnO, as recently discussed by Look and Claflin [Phys. Status Solidi B 241, 624 (2004)]. While ZnO already has many industrial applications owing to its piezoelectric properties and band gap in the near ultraviolet, its applications to optoelectronic devices has not yet materialized due chiefly to the lack of p-type epitaxial layers. Very high quality what used to be called whiskers and platelets, the nomenclature for which gave way to nanostructures of late, have been prepared early on and used to deduce much of the principal properties of this material, particularly in terms of optical processes. The suggestion of attainment of p-type conductivity in the last few years has rekindled the long-time, albeit dormant, fervor of exploiting this material for optoelectronic applications. The attraction can simply be attributed to the large exciton binding energy of 60meV of ZnO potentially paving the way for efficient room-temperature exciton-based emitters, and sharp transitions facilitating very low threshold semiconductor lasers. The field is also fueled by theoretical predictions and perhaps experimental confirmation of ferromagnetism at room temperature for potential spintronics applications. This review gives an in-depth discussion of the mechanical, chemical, electrical, and optical properties of ZnO in addition to the technological issues such as growth, defects, p-type doping, band-gap engineering, devices, and nanostructures.
Tập 98 Số 4 - 2005
General Theory of Three-Dimensional Consolidation The settlement of soils under load is caused by a phenomenon called consolidation, whose mechanism is known to be in many cases identical with the process of squeezing water out of an elastic porous medium. The mathematical physical consequences of this viewpoint are established in the present paper. The number of physical constants necessary to determine the properties of the soil is derived along with the general equations for the prediction of settlements and stresses in three-dimensional problems. Simple applications are treated as examples. The operational calculus is shown to be a powerful method of solution of consolidation problems.
Tập 12 Số 2 - Trang 155-164 - 1941
Các thông số dải cho các bán dẫn hợp chất III–V và hợp kim của chúng Chúng tôi trình bày một tổng hợp chi tiết và cập nhật về các thông số dải cho các bán dẫn hợp chất III–V có cấu trúc tinh thể zinct blende và wurtzite, bao gồm: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, và InN, cùng với các hợp kim bán dẫn ternary và quaternary của chúng. Dựa trên việc xem xét lại tài liệu hiện có, chúng tôi cung cấp các bộ thông số đầy đủ và nhất quán cho tất cả các vật liệu. Nhấn mạnh vào các thông số cần thiết cho các tính toán cấu trúc vùng, chúng tôi lập bảng các khe năng lượng trực tiếp và gián tiếp, các phân tách do spin-quỹ đạo và trường tinh thể, các tham số bifurcation của hợp kim, các khối lượng hiệu dụng cho điện tử, lỗ trống nặng, nhẹ, và lỗ tách, các tham số Luttinger, các yếu tố ma trận động lượng liên dải, và các tiềm năng biến dạng, bao gồm các phụ thuộc nhiệt độ và thành phần hợp kim khi có thể. Các sự lệch dải heterostructure cũng được cung cấp, trên một tỷ lệ tuyệt đối cho phép bất kỳ vật liệu nào có thể được cân chỉnh so với bất kỳ vật liệu nào khác.
Tập 89 Số 11 - Trang 5815-5875 - 2001
Contact and Rubbing of Flat Surfaces The interpretation of certain phenomena occuring at nominally flat surfaces in stationary or sliding contact is dependent on the assumed distribution of the real area of contact between the surfaces. Since there is little direct evidence on which to base an estimate of this distribution, the approach used is to set up a simple model and compare the deduced theory (e.g., the deduced dependence of the experimental observables on the load) with the experimental evidence. The main conclusions are as follows. (a) The electrical contact resistance depends on the model used to represent the surfaces; the most realistic model is one in which increasing the load increases both the number and size of the contact areas. (b) In general, mechanical wear should also depend on the model. However, in wear experiments showing the simplest behavior, the wear rate is proportional to the load, and these results can be explained by assuming removal of lumps at contact areas formed by plastic deformation; moreover, this particular deduction is independent of the assumed model. This suggests that a basic assumption of previous theories, that increasing the load increases the number of contacts without affecting their average size, is redundant.
Tập 24 Số 8 - Trang 981-988 - 1953
High-κ gate dielectrics: Current status and materials properties considerations Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward successful integration into the expected processing conditions for future CMOS technologies, especially due to their tendency to form at interfaces with Si (e.g. silicates). These pseudobinary systems also thereby enable the use of other high-κ materials by serving as an interfacial high-κ layer. While work is ongoing, much research is still required, as it is clear that any material which is to replace SiO2 as the gate dielectric faces a formidable challenge. The requirements for process integration compatibility are remarkably demanding, and any serious candidates will emerge only through continued, intensive investigation.
Tập 89 Số 10 - Trang 5243-5275 - 2001
A Powder Technique for the Evaluation of Nonlinear Optical Materials An experimental technique using powders is described which permits the rapid classification of materials according to
(a) magnitude of nonlinear optical coefficients relative to a crystalline quartz standard and
(b) existence or absence of phase matching direction(s) for second-harmonic generation.
Results are presented for a large number of inorganic and organic substances including single-crystal data on phase-matched second-harmonic generation in HIO3, KNbO3, PbTiO3, LiClO4·3H2O, and CO(NH2)2. Iodic acid (HIO3) has a nonlinear coefficient d14∼1.5×d31 LiNbO3. Since it is readily grown from water solution and does not exhibit optical damage effects, this material should be useful for nonlinear device applications.
Tập 39 Số 8 - Trang 3798-3813 - 1968
On differential equations of nonlocal elasticity and solutions of screw dislocation and surface waves Integropartial differential equations of the linear theory of nonlocal elasticity are reduced to singular partial differential equations for a special class of physically admissible kernels. Solutions are obtained for the screw dislocation and surface waves. Experimental observations and atomic lattice dynamics appear to support the theoretical results very nicely.
Tập 54 Số 9 - Trang 4703-4710 - 1983
The work function of the elements and its periodicity A new compilation, based on a literature search for the period 1969–1976, is made of experimental data on the work function. For these 44 elements, preferred values are selected on the basis of valid experimental conditions. Older values, which are widely accepted, are given for 19 other elements on which there is no recent literature, and are so identified. In the data for the 63 elements, trends that occur simultaneously in both the columns and the rows of the periodic table are shown to be useful in predicting correct values and also for identifying questionable data. Several illustrative examples are given, including verifications of predictions published in 1950.
Tập 48 Số 11 - Trang 4729-4733 - 1977