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Synthesis of Solids
Published in Elaine A. Moore, Lesley E. Smart, Solid State Chemistry, 2020
Elaine A. Moore, Lesley E. Smart
A molecular beam is a narrow stream of molecules formed by heating a compound in an oven with a hole, which is small compared to the mean free path of the gaseous molecules produced. Very thin layers can be built up by directing a beam of precursor molecules onto the substrate. The system is kept under ultrahigh vacuum. Because of the very low pressure, the reactants need not be as volatile as in other vapour deposition methods. An application of this method is the growth of single crystals for quantum cascade lasers, semiconductor lasers that emit in the far infrared. The first quantum cascade laser crystal contained nanometer-thickness layers of In0.52Al0.48As alternating with In0.53Ga0.47As, as shown in Figure 3.14. To make this crystal, beams of aluminium, gallium, arsenic, and indium are directed onto a substrate InP crystal. The substrate needs to be heated to allow the atoms deposited from the beams to migrate to their correct lattice position. The relative pressures of the component beams are adjusted for each layer to give the desired compositions.
Surface Phenomena
Published in Pramod K. Naik, Vacuum, 2018
Molecular beam epitaxy (MBE) involves the growth of single crystal films and high-purity semiconductor films, on top of a crystalline substrate using deposition of vapours evaporated from Knudsen effusion cells. The deposition is conducted in an ultrahigh vacuum environment to minimize possible contamination from the residual gases to achieve high-purity films. The deposition rate is such that a low growth rate of ~1 monolayer (lattice plane) per second is obtained. The evaporated atoms have long mean free paths and thus they cannot interact with each other or with residual gases in transit till they reach the substrate. A layer by layer growth is achieved. Joyce 44 has reviewed major aspects of MBE. Single-crystal gallium arsenide can be formed by heating highpurity gallium and arsenic simultaneously in separate Knudsen effusion cells to condense their vapours on the wafer where they react to form the compound 45. Many modern semiconductor devices are manufactured using the MBE technique. This technique is also used for deposition of oxide materials for electronic, magnetic and optical applications.
Molecular Beam Epitaxy with Gaseous Sources: Growth and Applications of Mixed Group V Compounds and Selective-Area Growth
Published in Jong-Chun Woo, Yoon Soo Park, Compound Semiconductors 1995, 2020
C.W. Tu, X.B. Mei, N.Y. Li, H.K. Dong
Molecular beam epitaxy (MBE), with solid sources, has been proven to be a versatile thin-film growth technique for research, development, and production of semiconductor materials. Most of its applications involve various heterostructures of arsenides. Because of the high vapor pressure of phosphorus, it is difficult to grow heterostructures with arsenide in one layer and phosphide in the adjacent layer or with mixed group V compouds. Before the recent development of valved crackers for solid arsenic and phosphorus sources[1,2,3], mixed group V compounds have been grown with gas-source MBE, where arsenic and phosphorus dimers are derived from cracked arsine and phosphine, respectively. Gas-source MBE thus extends the capability of solid-source MBE to be as flexible as organometallic vapor phase epitaxy (OMVPE). When the group III sources are also in gaseous form, selective-area growth (SAG) by an external energy source, e.g., an electron beam or a laser beam, or SAG on insulator-patterned substrates, where growth occurs only in the openings, can be achieved. SAG can improve device performance or realize novel devices. We shall first describe the growth of strained InAsxP1-x/InP and strain-compensated InASxP1-x/GayIn1-yP multiple quantum wells (MQWs) using elemental group III and doping sources and thermally cracked arsine and phosphine. These MQWs can be used for light modulation at 1.3 gm and even near 1.5 μm. When the group III sources are in gaseous forms, laser-assisted slective-area growth and doping, and issues of SAG on a patterned substrate, such as selectivity and sidewall facets, are discussed and SAG of an external base is applied to heterojunction bipolar transistors (HBTs).
Numerical simulation analysis of low energy proton irradiation mechanism of In x Ga1-x As (x = 0.2, 0.3, 0.53) solar cell
Published in Radiation Effects and Defects in Solids, 2022
S. Y. Zhang, Y. Zhuang, A. Aierken, Q. G. Song, X. Yang, X. N. Li, Q. Zhang, Y. B. Dou, Q. Wang
Figure 1 shows a schematic illustration of the InxGa1-xAs (x = 0.2, 0.3, 0.53) solar cell simulated in this study. All solar cell devices are 2.5 × 2.5 cm2 in size. We refer to the experimental parameters of In0.53Ga0.47As solar cell in our previous work as our simulation data, including the material, thickness, doping concentration and other parameters are shown in Figure 1. The experimental details of In0.53Ga0.47As solar cell can be seen in our previous work (17). The In0.53Ga0.47As solar cell was grown by MBE (molecular beam epitaxy) on InP substrate. The Si and Be were adopted as n-type and p-type doping sources of the solar cell, respectively. The base-layer and emitter-layer thickness of the InxGa1-xAs solar cell are 3 and 0.2 μm, respectively. The doping concentration of base-layer and emitter-layer are 1 × 1017 cm−3 and 1 × 1018 cm−3, respectively. The values of bandgap energy and lattice constant of InGaAs and InP materials are listed in Table 1. The anti-reflection coating (ARC) of MgF2/ZnS was adopted in this solar cell structure, which could increase the transmission of sunlight, and then improve the photocurrent of the solar cell.
Current conduction mechanisms in Au/a-Si:H(n+)/SiGe(n)/c-Si(p)/Ag hetero-junction solar cells
Published in Phase Transitions, 2022
We fabricated SiGe(n) thin-film layers on c-Si(p) substrates by molecular beam epitaxy (MBE) for hetero-junction solar cell applications. The simulated results of the dark forward current–voltage characteristics showed a thermoionic emission mechanism at low voltages and an SCLC mechanism at high voltages. It is demonstrated that the effect of shunt resistance is the dominated mechanism compared to the thermoionic effect when the measuring temperature decreases. The effective barrier height extracted from the dark characteristics is estimated at about 0.54 eV. This value is more confirmed than deduced from measurements at high frequency (1 MHz) and at room temperature.
Effect of solution Zn concentration on electrodeposition of CuxZn1–x alloys: materials and resistivity characterisation
Published in Transactions of the IMF, 2019
There are many techniques for fabrication of thin films. Some of these techniques are sputtering,14 flash evaporation,15 molecular beam epitaxy, etc. Among these techniques electrodeposition has advantages of applicability at room temperature, non-necessity for vacuum equipment, cost-effectiveness, among others. Moreover, there are many parameters which can be modified to obtain different material properties, making electrodeposition a versatile method of producing thin and thick films. There have been numerous studies for obtaining CuZn films via electrodeposition and understanding the relationships between process parameters and film properties.16–19 Some researchers have reported effects of deposition parameters and various additives on electrodeposition of CuZn films.20–24 A number of studies on CuZn film production by electrodeposition have given special emphasis on the shape memory property.25–27