After an introduction to inversion layers and a summary of the theoretical ideas concerning the expected effects of disorder in such systems, the observed behaviour near the threshold of conduction is reviewed. Although the system shows a classic metal-insulator transition, the detailed behaviour is not consistent with an independent-particle mobility edge model. A new model is proposed in which correlation causes the carriers to behave like a viscous liquid near the conduction threshold. The new model provides quantitative explanations of many observed properties. Other experiments are suggested by which it may be further tested.

http://iopscience.iop.org/article/10.1088/0022-3719/11/5/008/pdf

Threshold conduction in inversion layers

Measurements on n-type indium antimonide down to 0.3K are described of the resistivity in a magnetic field (0-40 kG) both parallel and perpendicular to the current, and of the Hall effect. Increases of resistivity by a factor of 1010 are observed before the resistivity becomes too high to measure provided special care is taken over the preparation of the surface of the specimen. A saturation of resistivity with increase of magnetic field is sometimes observed and this is attributed to the effect of a conducting surface layer. The resistivity approximates to the form rho -1= rho 01-1 exp(-E1/kT)+ rho 03-1 exp(-E3/kT). The E1 region is identified with magnetic freeze-out and the E3 region with electrons hopping between donor centres. Good agreement is obtained between theory and experiment for the magnetic field dependence of rho 03.

http://iopscience.iop.org/article/10.1088/0022-3719/11/20/012/pdf

Magnetoresistance and Hall effect in n-type indium antimonide in the magnetic freeze-out region

The collector-base junction avalanche in advanced n-p-n transistors in the temperature range of 293 to 83 K is described The multiplication factor is shown to increase exponentially with decreasing temperature The dependence decreases with increased collector doping concentration and, for the same device, with increased reverse bias At a fixed collector bias, it is roughly constant at low current density, but varies with I/sub c/ at high-level injection due to space-charge modulation Measurements at low temperatures excluded self-heating in the devices, and it was possible to study high-level injection effects at collector current densities higher than 10 mA/ mu m/sup 2/ Extensive computer simulations were performed to study the effects of the field and carrier distributions It was observed that, at very high current densities, when the injected carrier density in the collector junction exceeds 1*10/sup 17/ cm/sup -3/, there is an anomalous drop in the avalanche multiplication rate that conventional device simulators fail to predict The latter is attributed to electron-electron scattering that retards impact ionization by quickly redistributing the excess energy through interparticle collisions >

Low-temperature avalanche multiplication in the collector-base junction of advanced n-p-n transistors

The theory of impurity conduction is discussed and a summary is presented of some experimental aspects of the metal-insulator transition in impurity bands and inversion layers. The various transport mechanisms in the Fermi glass, and results from the literature, are reviewed showing how these mechanisms are affected by the application of a magnetic field.

Metal-insulator transitions induced by a magnetic field

Electrical conductivity measurements on n-type InSb in the temperature range 0.27-4.2 K and in magnetic fields up to 10 kG have been made. The results indicate a strong magnetic field dependence for the conductivity, with an activation energy depending on magnetic field. These results are discussed in the light of the recently proposed wigner transition which is appropriate to the highly compensated samples used in this work. The magnitude of the activation energy and the role of the first excited state of the impurity centre are also briefly considered.

https://iopscience.iop.org/article/10.1088/0022-3719/4/12/015/pdf

Electrical conductivity in n-type InSb as a function of magnetic field at 3He temperatures

Measurements of the longitudinal and transverse magnetoresistance and Hall coefficient of indium antimonide in the magnetic freeze-out range are described. For magnetic fields greater than 5 kG, the longitudinal magnetoresistance can be readily interpreted, assuming conduction is only due to electrons remaining in the conduction band. This is considered to be more plausible than the interpretation of the Hall coefficient used by previous authors, in which it is assumed that a two-band model can be used up to quite high fields. On the basis of conduction by a single band, values of the donor ionization energy as a function of magnetic field are calculated, with no adjustable parameters, and compared with the theory of Yafet, Keyes, and Adams.

http://iopscience.iop.org/article/10.1088/0022-3719/3/2/024/pdf

R Mansfield

Papers

Magnetic freeze-out effects in n-type indium antimonide