Electron-hole droplets

Plasma frequencies and the corresponding wavelengths for a range of free-electron densities are given in Table 9.2 the plasma effects mentioned in this section are noted beside the wavelengths (electron-hole droplets will be discussed in Chapter 12). 

Figure 12.21 Calculated far infrared extinction (arbitrarily normalized) by electron-hole droplets in Sb-doped germanium (from Rose et al., 1978) below which are experimental data (circles) of Timusk and Silin (1975).

Jeffries, C.D. Keldysh, L.V. Eds. Electron-Hole Droplets in Semiconductors North Holland Amsterdam, 1983. 

Electron—Hole Droplets in Semiconductors, C.D. Jef-fnes and L.V. Keldysh (Ed.), North-Holland, Amsterdam, 1983. 

At low temperatures a pure semiconductor is a perfect insulator with no free carriers. Upon laser irradiation at a frequency greater than the semiconducting band gap, a high density of electron-hole pairs can be excited which, at liquid-helium temperatures, condense into small droplets of electron-hole plasma. These electron-hole (e-h) droplets have been discussed thoroughly in a dedicated volume of Solid State Physics that contains reviews of theoretical aspects (Rice, 1977) and experiments (Hensel et al., 1977). 

American physicist Robert A. Millikan and his student Harvey Fletcher designed an experiment to determine the charge on the electron. As shown in Figure 2-14. the apparatus was a chamber containing two electrical plates. An atomizer sprayed a mist of oil droplets into the chamber, where the droplets drifted through a hole in the top plate. A telescope allowed the experimenters to measure how fast the droplets moved downward under the force of gravity. The mass of each droplet could then be calculated from its rate of downward motion. 

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