GTBL042-12 GTBL042-Callister-v2 August 13, 2007 18:22
474 • Chapter 12 / Electrical PropertiesTable 12.3 Band Gap Energies, Electron and Hole Mobilities, and Intrinsic
Electrical Conductivities at Room Temperature for
Semiconducting MaterialsBand Gap Electrical Conductivity Electron Mobility Hole Mobility
Material (eV)[(-m)−^1 ](m^2 /V-s)(m^2 /V-s)
Elemental
Si 1.11 4 × 10 −^4 0.14 0.05
Ge 0.67 2.2 0.38 0.18
III–V Compounds
GaP 2.25 — 0.03 0.015
GaAs 1.42 10 −^6 0.85 0.04
InSb 0.17 2 × 104 7.7 0.07
II–VI Compounds
CdS 2.40 — 0.03 —
ZnTe 2.26 — 0.03 0.01Semiconductivity
The electrical conductivity of the semiconducting materials is not as high as that of
the metals; nevertheless, they have some unique electrical characteristics that render
them especially useful. The electrical properties of these materials are extremely
intrinsic sensitive to the presence of even minute concentrations of impurities.Intrinsic semi-
semiconductor conductorsare those in which the electrical behavior is based on the electronic struc-
ture inherent in the pure material. When the electrical characteristics are dictated
extrinsic by impurity atoms, the semiconductor is said to beextrinsic.
semiconductor
12.10 INTRINSIC SEMICONDUCTION
Intrinsic semiconductors are characterized by the electron band structure shown in
Figure 12.4d: at 0 K, a completely filled valence band, separated from an empty
conduction band by a relatively narrow forbidden band gap, generally less than 2
eV. The two elemental semiconductors are silicon (Si) and germanium (Ge), having
band gap energies of approximately 1.1 and 0.7 eV, respectively. Both are found in
Group IVA of the periodic table (Figure 2.6) and are covalently bonded.^4 In addi-
tion, a host of compound semiconducting materials also display intrinsic behavior.
One such group is formed between elements of Groups IIIA and VA, for exam-
ple, gallium arsenide (GaAs) and indium antimonide (InSb); these are frequently
called III–V compounds. The compounds composed of elements of Groups IIB and
VIA also display semiconducting behavior; these include cadmium sulfide (CdS) and
zinc telluride (ZnTe). As the two elements forming these compounds become more
widely separated with respect to their relative positions in the periodic table (i.e.,
the electronegativities become more dissimilar, Figure 2.7), the atomic bonding be-
comes more ionic and the magnitude of the band gap energy increases—the materials
tend to become more insulative. Table 12.3 gives the band gaps for some compound
semiconductors.(^4) The valence bands in silicon and germanium correspond tosp (^3) hybrid energy levels for the
isolated atom; these hybridized valence bands are completely filled at 0 K.