Silicon hole concentration

Fig. 12. SIMS concentration profiles of B, H, and O in silicon. The inset shows the spreading resistance of this sample before (B) and after (A) hydrogenation. The hole concentration at the surface is 2.0 x 1019 cm-3 before and 1.4 x 1018 cm-3 after hydrogenation.

Germanium and silicon are electrolytically etched at about the same rate, about 3x10" 5 cm 3/coulomb. Thus at a current density of 500 ma/crn, Ge and Si are dissolved at the rate of about 1.7x10 cm/sec (0.0004 in /min). In order to electrolytically etch n-type semiconductors at a reasonable rate, some means must be found to increase the hole concentration at... 

The negative surface charge induced by the F species is balanced by a corresponding hole concentration in the silicon. Experimentally, the dependence of etch rate on dopant concentration is in the order ... 

Fig. 17. Energy scheme for pore formation in p-type silicon. At the pore base, the surface hole concentration is in quasi-equilibrium and increases exponentially as the Fermi level is lowered toward the flat hand condition (a). In the regions between the pores the minimum feature size is determined hy enlargement of the band gap due to quantum confinement holes are excluded from these regions, as shown in (b) [79].

The FIF-CrOs etching system is widely used for defect sensitive etching and delineation of junctions between silicon layers of different doping concentrations. The etch rate of silicon in pure FIF solution is very low due to the lack of holes at the OCR Addition of CrOs increases the etch rate due to the increase of surface hole concentration resulting from the reduction of Cr. CrOs dissolves in water to form... 

Fig. 1.1. Temperature-dependence of the ffee-hole concentrations p in three In-doped silicon samples measured by Hall effect. The fit of the curves shows that the dominant acceptor in sample 3 is isolated In (Ei = 153 meV) and the In-X centre (Ei = lllmeV) in samples 1 and 2. The compensating donor compensation Nd resulting from the fit is indicated (after [4]). Copyright 1977, American Institute of Physics...

This expression is derived from the more general case where the electron and hole concentrations in the conduction and valence bands are n and p with np = n2. At RT, taken as 300 K, the intrinsic carrier concentration n is 1.1 x 10111 cm in silicon, but it increases to about 4 x 1013 cm 3 in germanium to reach 2 x 1016 cm-3 in intrinsic InSb. 

In the extrinsic or doped semiconductor, impurities are purposely added to modify the electronic characteristics. In the case of silicon, every silicon atom shares its four valence electrons with each of its four nearest neighbors in covalent bonds. If an impurity or dopant atom with a valency of five, such as phosphorus, is substituted for silicon, four of the five valence electrons of the dopant atom will be held in covalent bonds. The extra, or fifth electron will not be in a covalent bond, and is loosely held. At room temperature, almost aU of these extra electrons will have broken loose from their parent atoms, and become free electrons. These pentavalent dopants thus donate free electrons to the semiconductor and are called donors. These donated electrons upset the balance between the electron and hole populations, so there are now more electrons than holes. This is now called an N-type semiconductor, in which the electrons are the majority carriers, and holes are the minority carriers. In an N-type semiconductor the free electron concentration is generally many orders of magnitude larger than the hole concentration. 

The hole concentration is known to be 2.0 X 10 m". Using the electron and hole mobilities for silicon in Table 18.3, compute the electron concentration. 

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