Electrons and Holes in Semiconductors

Under light illumination, semiconductor electrodes absorb the energy of photons to produce excited electrons and holes in the conduction and valence bands. Compared with photoelectrons in metals, photoexcited electrons and holes in semiconductors are relatively stable so that the photo-effect on electrode reactions manifests itself more distinctly with semiconductor electrodes than with metal electrodes. 

Schockley, 1950] W. Schockley, Electrons and Holes in Semiconductors, Van Nostrand, New York, (1950). 

Kayanuma Y (1988) Quantum size effects of interacting electrons and holes in semiconductor microciystals with spherical shape. Phys Rev B 38 9797-9805... 

W. Shoddey, Electrons and Holes in Semiconductors with Applications to Transistor Electronics, D. Van Nostrand Co., Inc., Princeton, N.J., 1950. 

As can be verified, Ep equals Therefore it has been shown that eqn (1.133) is identical to eqn (1.135). From this, the creation and annihilation of electrons and holes in semiconductors may be written as the following chemical equation... 

Thus, lattice defects such as point defects and carriers (electrons and holes) in semiconductors and insulators can be treated as chemical species, and the mass action law can be applied to the concentration equilibrium among these species. Without detailed calculations based on statistical thermodynamics, the mass action law gives us an important result about the equilibrium concentration of lattice defects, electrons, and holes (see Section 1.4.5). 

A photomultiplier tube is a sensitive detector of visible and ultraviolet radiation photons cause electrons to be ejected from a metallic cathode. The signal is amplified at each successive dynode on which the photoelectrons impinge. Photodiode arrays and charge coupled devices are solid-state detectors in which photons create electrons and holes in semiconductor materials. Coupled to a polychromator, these devices can record all wavelengths of a spectrum simultaneously, with resolution limited by the number and spacing of detector elements. Common infrared detectors include thermocouples, ferroelectric materials, and photoconductive and photovoltaic devices. 

Studies on luminescence of CdS colloids provide useful knowledge on the energy and nature of recombination sites of charge carriers in the colloidal particles. The regularities of the colloid photoluminescence quenching provide the information on the dynamics of electrons and holes in semiconductor particles as well as on the kinetics of interfacial electron transfer. Of a particular interest are studies on the luminescence of colloidal solutions of the so-called Q-semiconductors, their properties depending on the size of semiconductor particles due to the quantum size effects. 

Refs. [i] Shockley W (1950) Electrons and holes in semiconductors. Van Nostrand, New York [ii] Blakemore JS (1987) Semiconductor statistics. Dover, New York [Hi] Rhoderick EH (1978) Metal-semiconductor contacts. Clarendon Press, Oxford [iv] Ashcroft W, Mermin ND (1976) Solid state physics. Saunders College, Philadelphia [v] SeegerK (1991) Semiconductor physics - an introduction. Springer, Berlin... 

D. B. Bonham and M. E. Orazem, "Activity Coefficients of Electrons and Holes in Semiconductors with a Parabolic Density of States," Journal of The Electrochemical Society, 133 (1986) 2081-2086. 

The fact that shallow p- and n-type dopants of germanium could be considered as H-like atoms emerged at the end of the 1940s to explain the electrical conductivity of this material, and this was clearly expressed by William Shockley in his monograph Electrons and holes in semiconductors , first published in 1950. 

This relationship for Frenkel excitons was derived in (14) it can be seen from its derivation that it is independent of the model and, therefore, is valid also for ground state large-radius excitons as well as for electrons and holes in semiconductors. 

Figure 12.23 shows that, in small molecules, electrons occupy discrete molecular orbitals whereas in macroscale solids the electrons occupy delocalized bands. At what point does a molecule get so large that it starts behaving as though it has delocalized bands rather than localized molecular orbitals For semiconductors, both theory and experiment tell us that the answer is roughly at 1 to 10 nm (about 10—100 atoms across). The exact number depends on the specific semiconductor material. The equations of quantum mechanics that were used for electrons in atoms can be applied to electrons (and holes) in semiconductors to estimate the size where materials undergo a crossover from molecular orbitals to bands. Because these effects become important at 1 to 10 nm, semiconductor particles with diameters in this size range are called quantum dots. 

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