The photoconductivity of GaAs structures delta-doped by Sn has been investigated for wavelengths lambda= 650-1200 nm in the temperature interval T= 4.2-300 K. The electron densities and mobilities, before and after illumination, have been determined by magnetoresistance, Shubnikov-de Haas effect and Hall effect measurements, in high magnetic fields. For the heavily doped structures (n_H> 2x10^13 cm^-2) we observe under illumination by light with wavelengths larger than the band-gap wavelength of the host material (lambda= 815 nm at T= 4.2 K) first positive (PPPC) and then negative (NPPC) persistent photoconductivity. The NPPC is attributed to the ionisation of DX centres and PPPC is explained by the excitation of electrons from Cr impurity states in the substrate. For lambda< 815 nm in addition the excitation of electron over the band gap of GaAs contributes to the PPPC. For the lightly doped structures (n_H<= 2x10^13 cm^-2) the photoconductivity effect is always positive.

We have prepared a number of GaAs structures delta-doped by Sn using the well-known molecular beam epitaxy growth technique. The samples obtained for a wide range of Sn doping densities were characterised by magnetotransport experiments at low temperatures and in high magnetic fields up to 38 T. Hall-effect and Shubnikov-de Haas measurements show that the electron densities reached are higher than for other delta-dopants, like Si and Be. The maximum carrier density determined by the Hall effect equals 8.4x10^13 cm^-2. For all samples several Shubnikov-de Haas frequencies were observed, indicating the population of multiple subbands. The depopulation fields of the subbands were determined by measuring the magnetoresistance with the magnetic field in the plane of the delta-layer. The experimental results are in good agreement with selfconsistent bandstructure calculations. These calculation shows that in the sample with the highest electron density also the conduction band at the L point is populated.

The effect of illumination with various wavelengths λ (770 nm<λ<1120 nm) on the conductivity of GaAs structures with tin δ-doping of the vicinal faces was investigated in the temperature range 4.2–300 K. Negative persistent photoconductivity was found in strongly doped samples. It was shown on the basis of the results of investigations of the Hall and Shubnikov-de Haas effects that the negative photoconductivity is due to a large decrease in the electron mobility with increasing electron density. The decrease of electron mobility is explained by ionization of DX centers, which destroys the spatial correlation in the distribution of positively charged donors and negatively charged DX centers.

The photoconductivity of GaAs structures δ-doped by Sn has been investigated as function of wavelength (λ= 650-1200 nm) in the temperature interval T= 4.2-300 K. High-field magnetotransport experiments have been carried out in order to determine the electron densities and mobilities before and after illumination. For the heavily doped structures (n H > 2×10 13 cm-2) we observe under illumination by light with wavelenghts larger than the band-gap wavelength of the host material (λ= 815 nm at T= 4.2 K) first positive (PPPC) and then negative (NPPC) persistent photoconductivity. The NPPC is attributed to the ionisation of DX centres and PPPC is explained by the excitation of electrons from Cr impurity states in the substrate. For λ< 815 nm in addition the excitation of electron over the band gap of GaAs contributes to the PPPC. For the lightly doped structures (n H < 2×10 13 cm-2) the photoconductivity effect is always positive.

The transport and optical properties of tin δ layers in GaAs are investigated as functions of the Sn concentration. The Shubnikov-de Haas and Hall effects are measured in the temperature range 0.4–12 K in magnetic fields up to 38 T. The band diagrams and quantum mobilities of electrons in the quantum-well subbands are calculated. Features associated with electronic transitions from quantum-well levels are found in the photoluminescence spectra of the structures. Oscillations of the resistance are observed in a magnetic field parallel to the δ layer and are attributed to features in the density of states at the Fermi level.

A method of fabricating quasi-1D conducting wires of tin embedded in an i-GaAs matrix has been developed. The method involves forming a system of steps on vicinal surface of the GaAs(Cr) substrate misoriented 0.3° or 1° from the (001) plane forward to the (110) basal plane and decorating the ends of these steps with Sn through molecular-beam epitaxy. Transport properties of structures were measured in the temperature range 4.2–300 K at high electric fields up to E=104 V/cm using a pulse technique.

We have investigated the magnetotransport properties of vicinal (001) GaAs structures misoriented by 3° towards the (110) direction. The structures are δ-doped with Sn which predominantly accumulates at the step edges. In this way a dense array of 1D channels (d=54 Å) is formed. Shubnikov–de Haas oscillations show the presence of several subbands. A clear anisotropy in the electronic parameters is observed for a current ‖ and ⊥ to the step edges, notably R⊥/R‖∼1.5 (at T=4.2 K) for a sample with an electron density nHall=8×1012 cm−2. We have also found a significant anisotropy in nHall, μHall and nSdH. The difference in nHall and μHall could be explained by preferential scattering in one direction, caused by a preferential attachment of the Sn atoms on the step edges. For the difference in nSdH there is no clear explanation.