Band gap engineering

Because many devices use SiGe alloys to accelerate or trap charges in either the conduction band edge or the valence band edge, it is important to know the band offsets in addition to the bandwidths. Various measurements of band offsets have been reviewed recently along with a detailed theoretical model of band edge behaviors in strained and unstrained films. [17] The results indicate a valence band offset of 0.22 eV for Si on Ge and 0.74 eV for Ge on Si. One might expect that these values should be identical. For a truly unstrained system the band offset in one 

This formula results in a valence band offset of 0.53 eV for pure Ge on Si, which is equal to the 0.58 eV average of Van der Walle, within the reliability of the formulas. The same group concluded that the corresponding conduction band offset should be 

Both Equations 6.19 and 6.20 apply to strain-free structures. 

The strained cases are most clearly dealt with in the review by Van der WaUe, [17] although many other treatments are available in the literature. The result, however, is relatively simple for strained alloy layers on Si substrates - virtual all the band offset is accommodated in the valence band. This turns out to be paitieularly advantageous for design of certain bipolar junction transistors, as we shall see later. 

The reader is cautioned that band offsets have traditionally been hotly debated and are highly sensitive to individual measurements and materials preparation methods. The most reliable method for establishing the offsets has traditionally been to model the performance of heterojunction devices, which have performances that depend strongly on the offset values. Photoelectron spectroscopy is easier to use but more subject to experimental errors. The behavior that you observe may vary. 

---

Capasso F., Band-Gap Engineering From Physics and Materials to New emiconductor Devices, Science, 1987 235 172-176. 

F. Capasso, Graded-Gap and Superlattice Devices by Band-gap Engineering W. T. Tsang, Quantum Confinement Heterostructure Semiconductor Lasers... 

A large fraction of the material science research, and an important chapter of solid state physics are concerned with interfaces between solids, or between a solid and a two dimensional layer. Solid state electronics is based on metal-semiconductor and insulator-semiconductor junctions, but the recent developments bring the interface problem to an even bigger importance since band gap engineering is based on the stacking of quasi two dimensional semiconductor layers (quantum wells, one dimensional channels for charge transport). 

Han M, Ozyihnaz B, Zhang Y et al (2007) Energy band-gap engineering of graphene nanoribbons. Phys Rev Lett 98 206805... 

Semiconductor particle formation between Langmuir-Blodgett (LB) films is an alternative and promising approach to band-gap engineering [662-666]. The ease of formation of self-assembled (SA) films [183-185,203-246] promoted the incorporation of semiconductors into these media [663, 710]. 

Several research approaches are pursued in the quest for more efficient and active photocatalysts for water splitting (i) to find new single-phase materials, (ii) to tune the band-gap energy of TJV-active photocatalysts (band-gap engineering), and (iii) to modify the surface of photocatalysts by deposition of cocatalysts to reduce the activation energy for gas evolution. Obviously, the previous strategies must be combined with the control of the s)mthesis of materials to customize the crystallinity, electronic structure, and morphology of materials at nanometric scale, as these properties have a major impact on photoactivity. 

Liang YQ, Zhai L, Zhao XS, Xu DS (2005) Band gap engineering of semiconductor nanowires through composition modulation. J Phys Chem B 109 7120-7123... 

Because the dimensions of the quantum well can be varied, the emission spectmm can be varied or tuned. This feature, in quantum wells and in quantum wires and dots, discussed below, is called band-gap engineering. 

A. M. Smith, S. Nie, Semiconductor Nanocrystals Structure, Properties, and Band Gap Engineering. Accounts of Chemical Research 2010, 43,190-200. 

Controlling Parameters in Photonic Crystals In order to develop an optofluidic characterization technique based on a photonic crystal, parameters for band-gap engineering must be established ... 

Wilson, J.N., et al. 2002. Band gap engineering of poly(p-phenyleneethynylene)s Cross-conjugated PPE-PPV hybrids. Macromokcules 35 8681. 

---