Impurity states and electron transport in gapless semiconductors

Abstract

Specific features of transport phenomena in gapless semiconductors which are due to both peculiarities of the electron spectrum of an ideal crystal and those of the impurity states in these semiconductors, are discussed. A detailed critical analysis is made of a large number of experimental papers dealing with studies of the conductivity, Hall effect, and magnetores]stance in HgCdTe crystals as a function of temperature, pressure, and magnetic field. On the strength of this analysis it is concluded that the perturbing action of the potential of acceptor-type impurities leads to effective overlap of the valence band with the conduction band. As a result, when the impurity concentration is sufficiently high, and exceeds that at which the Mott-Anderson transition occurs, the density of states of a p-type zero-gap semiconductor differs substantially from that of an ideal crystal, and is similar to that of a semimetal.

A quasi-zero-gap semiconductor at high pressures as a model of amorphous semiconductor

“…In the temperature range 2-300 К and excess acceptor concentration range 10 10 -10 17 cm -3 , complex measurements of the dependences of the kinetic coefficients on the uniform pressure (up to 1.5 GPa) and electric (up to 250 V/cm) and magnetic (up to 20 kOe) fields are performed for the p-type quasi-zero-gap Ge<Au 2-> [7], InAs с (N A -N D ) < 10 17 cm -3 [8], InSb<Cr> [9], and CdSnAs 2 <Cu> [4,[13][14][15][16][17][18] with the acceptor band filling coefficient 0 On the basis of the temperature, pressure, and field dependences of the Hall coefficient R(T, P, H) and specific conductivity σ(T, P), the partial values of the Hall coefficient R j and specific conductivity σ j were calculated using the well-known phenomenological relations of the universal model assuming additivity of contributions from partial conductivities to the total conductivity and independence of the relaxation time of energy [1, 4,12,18,19]. The energy dependence of the conduction-band state density in the vicinity of its unperturbed minimum was calculated in the energy range about the typical random-potential amplitude using the formula derived in [20] in the approximation of nonlinear screening (see also [21]).…”

“…The р-type Ge<Au 2-> [7], InAs with the excess acceptor concentration (N A -N D ) < 10 17 cm -3 [8], InSb [9,10] and InAs [11] doped by chromium, narrow-gap CdHgTe [12], and CdSnAs 2 <Cu> [4,[13][14][15][16][17][18] semiconductors are quasizero-gap semiconductors.…”

Bands and Bandgaps in Solids

“…Examples include gray tin with a gap of 0-0.08 eV (suggested by magneto-optical experiments; (Pidgeon 1969)) and lead chalcogenides and their alloys with other II-VI compounds or with SnTe and mercury chalcogenides. For a review, see Tsidilkovski et al (1985). The lead chalcogenides are characterized by a small bandgap with a maximum of the valence band and a minimum of the conduction band at the L point rather than the G point which is the case for most other direct-gap semiconductors (Section 2 of chapter "▶ Band-to-Band Transitions") with E g and m n as shown in Table 2.…”

10.1007/s11446-008-3001-8

“…1), have negative pressure coefficients: β = < 0 (ε g = ε É6 -ε É8 ) [13]. For example, experimental data on the temperature, pressure, and magnetic-field dependences of the Hall coefficient R(T, H, P) and conductivity σ(T, H, P) were used to determine the values of β for slightly doped (p-HgTe-2) [14] and heavily doped [15] mercury telluride samples (Fig.…”