Epitaxial deposition techniques

Epitaxial crystal growth methods such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) have advanced to the point that active regions of essentially arbitrary thicknesses can be prepared (see Thin films, film deposition techniques). Most semiconductors used for lasers are cubic crystals where the lattice constant, the dimension of the cube, is equal to two atomic plane distances. When the thickness of this layer is reduced to dimensions on the order of 0.01 )J.m, between 20 and 30 atomic plane distances, quantum mechanics is needed for an accurate description of the confined carrier energies (11). Such layers are called quantum wells and the lasers containing such layers in their active regions are known as quantum well lasers (12). 

The electrochemical atomic layer epitaxy (ECALE) technique, also known as electrochemical atomic layer deposition (EC-ALD), is based on layer-by-layer electrodeposition. Each constituent of the thin him are deposited separately using underpotential deposition (UPD) of that element. UPD is a process wherein an atomic layer of one element is deposited on the surface of a different element at a potential under that needed to deposit the element on itself. ECALE has been used to grow mainly II-VI and III-V compounds. A thorough review of ECALE research has been published by Stickney.144 A summary of the materials deposited using ECALE are given in Table 8.4, with a more detailed discussion for a few select examples given below. 

Thin semiconductor films (and other nanostructured materials) are widely used in many applications and, especially, in microelectronics. Current technological trends toward ultimate miniaturization of microelectronic devices require films as thin as less than 5 nm, that is, containing only several atomic layers [1]. Experimental deposition methods have been described in detail in recent reviews [2-7]. Common thin-film deposition techniques are subdivided into two main categories physical deposition and chemical deposition. Physical deposition techniques, such as evaporation, molecular beam epitaxy, or sputtering, involve no chemical surface reactions. In chemical deposition techniques, such as chemical vapor deposition (CVD) and its most important version, atomic layer deposition (ALD), chemical precursors are used to obtain chemical substances or their components deposited on the surface. 

ZnO thin films can be prepared by a variety of techniques such as magnetron sputtering, chemical vapor deposition, pulsed-laser deposition, molecular beam epitaxy, spray-pyrolysis, and (electro-)chemical deposition [24,74]. In this book, sputtering (Chap. 5), chemical vapor deposition (Chap. 6), and pulsed-laser deposition (Chap. 7) are described in detail, since these methods lead to the best ZnO films concerning high conductivity and transparency. The first two methods allow also large area depositions making them the industrially most advanced deposition techniques for ZnO. ZnO films easily crystallize, which is different for instance compared with ITO films that can... 

Experimental determinations of barrier heights on oxide semiconductor interfaces using photoelectron spectroscopy are rarely found in literature and no systematic data on interface chemistry and barrier formation on any oxide are available. So far, most of the semiconductor interface studies by photoelectron spectroscopy deal with interfaces with well-defined substrate surfaces and film structures. Mostly single crystal substrates and, in the case of semiconductor heterojunctions, lattice matched interfaces are investigated. Furthermore, highly controllable deposition techniques (typically molecular beam epitaxy) are applied, which lead to films and interfaces with well-known structure and composition. The results described in the following therefore, for the first time, provide information about interfaces with oxide semiconductors and about interfaces with sputter-deposited materials. Despite the rather complex situation, photoelectron spectroscopy studies of sputter-deposited... 

Atomic layer deposition, also known as atomic layer epitaxy (Suntola and Antson, 1977), is a chemical vapor deposition technique capable of producing extremely thin uniform films (Ritala and Leskela, 2001 Leskela and Ritala, 2003). The method differs from conventional chemical vapor deposition in that the precursors, of which there are typically two, are not exposed to the substrate simultaneously. Rather, the first precursor is introduced into the reaction chamber, where it binds to the substrate at complete monolayer coverage a Langmuir... 

The potential benefits of CVD over other film deposition techniques are that CVD-derived films can be deposited under conditions that give conformal coverage, they can be deposited at low temperatures, there can be a high level of compositional control, thin layers can be deposited, the technique can be scaled to coat large areas uniformly, and there is also the possibility for area-selective deposition13 as a result of the chemical nature of this process. The details of CVD and related chemical deposition processes such as atomic layer epitaxy (ALE), organometallic vapor-phase epitaxy (OMVPE), and others have been described elsewhere.6... 

The modern microelectronics and semiconductor industries have imposed severe demands on the quality of films produced by the silicon epitaxy process and the epitaxial film deposition techniques need to fulfill several general... 

One of the most investigated high Tc superconductors is YBa2Cu307 t (YBCO). The discovery of this superconductor initiated a worldwide effort to optimize the quality of thin films on different types of planar substrate using various deposition techniques, for example pulsed laser deposition, magnetron sputter deposition, co-evaporation and molecular beam epitaxy. It should be... 

Several techniques have been reported and, at the present time, the vapor phase deposition processes operating at temperatures around 300 °C are the most used. Thus II-VI compounds films like CdS, CdSe, CdTe, ZnS, ZnSe, and ZnTe have been grown epitaxially on Si, InP, GaAs, GaP, by molecular beam epitaxy (MBE) [204-207], by metal organic chemical vapor deposition (MOCVD) [208-210], or by pulsed laser deposition [211, 212]. Epitaxial deposition from aqueous solutions at low temperatures (< 100 °C) represents another approach. Specific beneficial effects may be also expected due to the simplicity of the process involving low cost investments. On the other hand the low temperature has for consequence the absence of interdiffusion processes around interfaces and the interfacial properties of the solids in contacts with solutions implicate excellent coverage properties at low thicknesses. Different... 

---