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 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.

This paper reports the measurements of high electric field transport and the persistent photoconductivity in delta-doped by Sn on vicinal and singular substrate GaAs structures. Transport properties of the hot electron gas were measured in the temperature range 4.2 K < T < 300 K at high electric fields up to E = 104 V/cm in darkness and under illumination using a pulse technique. Dependence of the current density J(E) showed an anisotropy in [1 1 0] and [1− 1 0] directions in GaAs(δ-Sn) on vicinal substrate structures and histeresis in electric field at low temperatures. In GaAs(δ-Sn) on singular substrate structures the anisotropy of conductivity is small. The persistent photoconductivity was observed with well defined threshold Tc ≈ 240 K in GaAs(δ-Sn) on vicinal substrate structures. At T = 4.2 K by applying a high voltage the persistent photoconductivity may be quenched and the resistance of the sample increased by an order of magnitude. The high conductivity state arises again due to illumination of the sample or due to heating to temperatures above ≈ 240 K.

We report the measurements of high electric field quenching of the persistent photoconductivity in delta-doped by Sn on vicinal substrate GaAs structures. Transport properties of the hot 2D electrons have been measured in the temperature range 4.2 K < T < 300 K at high electric fields up to E = 10(4) V/cm in darkness and under illumination using a pulse technique. The persistent photoconductivity was observed with well defined threshold T-c approximate to 240 K. At T = 4.2 K applying a high voltage the persistent photoconductivity may be quenched and the resistance of sample increased by an order of magnitude. The high conductivity stare arises again due to illumination of the sample or due to heating to temperatures above approximate to 240 K.

We synthesised and investigated new high-carrier-density GaAs/GaAlAs heterostructures with combined doping, that is with delta-doping by Si of GaAs and uniform doping by Si of GaAlAs layers. The Hall effect and magnetoresistance were investigated for the structures with distances L-delta between heterojunction and delta-layer from 200 Angstrom, to 1200 Angstrom. The enhanced 2D electron concentration achieved was 1.1*10(-13) cm(-2) in six filled subbands for the sample with L-delta=750 Angstrom. Electron mobilities and concentrations in each 2D subband have been extracted from the magnetoresistance and fall effect data. The electron mobility due to the scattering from ionized impurities has been calculated in the case when several subband are occupied.

The conductivity of GaAs structures δ-doped with tin on the vicinal and singular faces was investigated in strong electric fields up to E=104 V/cm and temperatures in the range 4.2 K <T<300 K. The measurements were performed in the dark and under illumination with visible light. Long-time photoconductivity of 2D electrons with threshold T c ≈240 K was observed in samples which were δ-doped with tin on the vicinal face. A strong electric field not only quenches photoconductivity, but also increases the resistance of the structures at temperatures T<T c by several orders of magnitude with respect to the dark resistance.