Gapless semiconductors, semiconductors with a forbidden-band width Εg = 0. Gapless semiconductors of two types occur:
1) the absence of a forbidden band is due to the symmetry of the crystals and to the degeneracy of the electron states (see Band theory); examples of such gapless semiconductors— α-Sn, HgTe and HgSe (Fig.);
2) Εg =0 only under certain conditions (pressure, temperature, the concentration of the components in the case of a solid solution and so on). The most typical representatives — the alloys Bi—Sb, the systems CdxHg1-xTe, Pb1-x Snx Te and others.
Dependence of the energy Ε on the quasi-momentum p for gapless semiconductors of the first type:
a - the conduction band;
b - the valence band.
In gapless semiconductors of the second type the mobility of the carriers reaches record values, which makes it easier to observe a number of kinetic effects in electric and magnetic fields. The question of the insulator — metal phase transition is connected with these gapless semiconductors; they are used in semiconductor device engineering (infrared radiation detectors, cooling devices and others). Gapless semiconductors of the first type form a kind of boundary between semimetals and semiconductors. Since in gapless semiconductors no activation energy is needed for electrons to pass from the valence band to the conduction band, they have a high permittivity. A comparatively weak electric field increases the concentration of mobile charge carriers, leading to a substantial departure from Ohm's law. In gapless semiconductors the Coulomb interaction of the electrons with one another and with impurity ions plays a greater part than in ordinary semiconductors. Such gapless semiconductors have as yet found no practical application.
1) the absence of a forbidden band is due to the symmetry of the crystals and to the degeneracy of the electron states (see Band theory); examples of such gapless semiconductors— α-Sn, HgTe and HgSe (Fig.);
2) Εg =0 only under certain conditions (pressure, temperature, the concentration of the components in the case of a solid solution and so on). The most typical representatives — the alloys Bi—Sb, the systems CdxHg1-xTe, Pb1-x Snx Te and others.
Dependence of the energy Ε on the quasi-momentum p for gapless semiconductors of the first type:
a - the conduction band;
b - the valence band.
In gapless semiconductors of the second type the mobility of the carriers reaches record values, which makes it easier to observe a number of kinetic effects in electric and magnetic fields. The question of the insulator — metal phase transition is connected with these gapless semiconductors; they are used in semiconductor device engineering (infrared radiation detectors, cooling devices and others). Gapless semiconductors of the first type form a kind of boundary between semimetals and semiconductors. Since in gapless semiconductors no activation energy is needed for electrons to pass from the valence band to the conduction band, they have a high permittivity. A comparatively weak electric field increases the concentration of mobile charge carriers, leading to a substantial departure from Ohm's law. In gapless semiconductors the Coulomb interaction of the electrons with one another and with impurity ions plays a greater part than in ordinary semiconductors. Such gapless semiconductors have as yet found no practical application.