Bands epitaxy

The main advantages that compound semiconductor electronic devices hold over their siUcon counterparts He in the properties of electron transport, excellent heterojunction capabiUties, and semi-insulating substrates, which can help minimise parasitic capacitances that can negatively impact device performance. The abiUty to integrate materials with different band gaps and electronic properties by epitaxy has made it possible to develop advanced devices in compound semiconductors. The hole transport in compound semiconductors is poorer and more similar to siUcon. Eor this reason the majority of products and research has been in n-ty e or electron-based devices. 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

The ECALE synthesis of V-VI (V Sb, Bi) compounds has been attempted in a few works. Antimony telluride, Sb2Te3, nanofilms with a homogeneous microstructure and an average size of about 20 nm were formed epitaxially on a Pt substrate [61]. The optical band gap of these films was blue-shifted in comparison with that of the bulk single-crystal Sb2Tc3 compound. 

Mg2+ ion. 49 has been used to deposit MgO by atomic layer epitaxy,222 and is commonly employed as a />-type dopant for semiconductors, particularly GaAs,223 GaN,224,225 and AlGaN.226 In GaN, Mg doping induces a blue 2.8 eV photoluminescence band arising from donor-acceptor (D-A) pair recombination.227 It is likely that isolated Mg... 

Equation (10.1) can be used to determine the doping density of a silicon substrate and its depth profile, even if the flat band potential is not known accurately. Diffusion doping, ion implantation or the growth of an epitaxial layer are common methods of producing doped regions in semiconductor substrates. The dopant concentration close to the surface can be measured by SRP or capacitance-... 

Fig. 16.4 (a) The crystal ceiis of anatase Ti02. (b) View of the octahedra-packing of anatase Ti02 the thick red lines indicate the axis in representative octahedra which, under stress, results in a change of band gap. (c) Band gap variation in anatase Ti02 under hydrostatic, epitaxial, and uniaxial stress. Adapted from Yin etal. [72] with kind permission from American Institute of Physics (2010). 

An important featnre to note in double-axis topography experiments is that when the beam area is large, the measnred rocking curve widths are not necessarily intrinsic. For example, mismatched epitaxial layers curve substrate wafers by an amonnt which depends on the degree of mismatch and layer thickness. Topographs of snch curved wafers show bands of diffracted intensity. 

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