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Review of Solid State Physics
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
Energy bands have maxima and minima when defined by energy and crystal momentum in what are known E-k diagrams. Empty states in the valence band are treated as positive particles called “holes”. Because electrons need only lose energy to recombine with a hole in direct band gap semiconductors, the charge carriers have high recombination probabilities, thereby causing short charge carrier lifetimes. Electrons must change both momentum and energy to recombine with holes for semiconductors with indirect band gaps; hence, the charge carrier lifetimes are generally longer than observed for direct band-gap materials. Bands with sharp curvature d2E/dk2 cause the charge carrier effective mass for electrons or holes to decrease. Small effective mass increases the charge carrier mobility. The electrical behavior of semiconductors can be controlled by introducing dopant impurities. Deep dopants can be added into material to increase resistivity and reduce leakage currents in such a way that the material performs in a similar fashion as intrinsic material. The introduction of excess impurities or defect centers causes a reduction in charge carrier lifetime.
HgCdTe Detectors
Published in Antoni Rogalski, Infrared and Terahertz Detectors, 2019
Initially, several isolated experimental reports were published to verify the predicted small values of k = αh/αe (<0.1) in Hg1−xCdxTe with λc longer than 1.9 μm [397,398]. One of the earliest studies of the electron-initiated multiplication on a LWIR HgCdTe (λc = 11 μm) showed that reasonable gains could be obtained at low voltages (5.9 at −1.4 V) [369]. However, the clear and compelling advantages of the electron-initiated avalanche process in MWIR lateral-collection n+-n−-p (with p-type absorber regions) were first reported in 2001 by Beck et al. [399]. Soon, thereafter, a theory by Kinch et al. [400] substantiated by Monte Carlo simulations by the University of Texas group [401] has been used to develop an empirical model to fit the experimental data obtained at DRS Infrared Technologies. The large inequity between αe and αh results from three key features of the HgCdTe energy band structure: (i) the electron effective mass is much smaller than the heavy hole effective mass (electrons have a much higher mobility), (ii) a much lower scattering rate by optical phonons, and (iii) a factor-of-two lower ionization threshold energy (there are no subsidiary minima in the conduction band to which energetic electrons can scatter; and the light holes are not important).
Varactors
Published in Mike Golio, RF and Microwave Semiconductor Device Handbook, 2017
Common conventional varactors at lower frequencies are reverse biased semiconductor abrupt p+-n junction diodes made from GaAs or silicon.2 However, metal-semiconductor junction diodes (Schottky diodes) are superior at high frequencies since the carrier transport only relies on electrons (unipolar device). The effective mass is lower and the mobility is higher for electrons compared to holes. Furthermore, the metal-semiconductor junction can be made very precisely even at a submicron level. A reverse biased Schottky diode exhibits a nonlinear capacitance with a very low leakage current. High frequency diodes are made from GaAs since the electron mobility is much higher than for silicon.
Band structure and chemical bonding of GaP: pressure-induced effects
Published in Phase Transitions, 2020
N. Bouarissa, H. Algarni, F. Mezrag, M. Ajmal Khan
The effective mass is a quantity that is used to simplify band structures by modeling the behavior of a free particle with that mass. It is an important parameter that describes most carrier transport properties [38,39]. Experimentally, it is often determined from cyclotron resonances or transport measurements [39]. Theoretically, it can be obtained using various methods with various degrees of sophistication ranging from empirical to ab initio calculations [40–44]. In the current contribution, the electron effective mass at the Г point of the Brillouin zone in GaP has been calculated at different pressures ranging from 0 up to 100 kbar. The used procedure is similar to that used by Bouarissa [45], where the electron effective mass is determined from the electronic band structure by taking few k points near the minimum of the first conduction band and using the relation,