E. Skuras

Anisotropic piezoelectric effect in lateral surface superlattices

We have studied the potential induced by lateral surface superlattices deposited on a GaAs/AlGaAs heterostructure as a function of bias and orientation of the gates. By using the gates to null the total potential, we extracted the contribution to this potential in the absence of gate bias. Its angular dependence shows that it is dominated by strain from the gates coupled to the electrons by the piezoelectric effect.

Anharmonic periodic modulation in lateral surface superlattices

Abstract We have measured the longitudinal magnetoresistance of a lateral surface superlattice with a period of 270 nm where the electrons are only 28 nm deep. The commensurability oscillations have a strong second harmonic content. This reflects a non-sinusoidal potential in the two-dimensional electron gas, a consequence of the shallow structure. The shape of the potential cannot be explained by a pinned GaAs surface and indicates that the surface charge is frozen or that the electrons feel an elastic strain field from the metal gates.

1.2 K Shubnikov–de Haas measurements and self‐consistent calculation of silicon spreading in δ‐ and slab‐doped In0.53Ga0.47As grown by molecular beam epitaxy

Magnetotransport measurements are reported for In0.53Ga0.47As layers grown by molecular beam epitaxy (MBE) at different substrate temperatures (Ts) and either δ‐ or slab‐doped with Si. Multiple subband densities deduced from the Fourier analysis of 1.2 K Shubnikov–de Haas measurements are compared with those derived from self‐consistent calculations which include nonparabolicity and the doping profile width wSi as a fitting parameter. Significant spreading of the Si donors away from the doping plane is deduced for deposition at Ts≊520 °C, while no measurable migration is inferred for Ts≤470 °C, leading to near‐ideal δ‐doping behavior. Contrary to previous results [McElhinney et al., J. Cryst. Growth 150, 266 (1995)], no evidence for amphoteric behavior has been found for Si areal densities up to 4×1012 cm−2.

Electron transport in shallow heterostructures with AlGaAs and AlAs barriers

Two series of shallow GaAs heterostructures, with AlGaAs and AlAs barriers respectively and both delta -doped with around 4*1016 m-2 Si donors, have been studied using low-temperature magnetotransport techniques. The electrons in these structures were confined against interfaces 28 nm from the surface. The AlGaAs barrier samples depleted at a uniform rate with bias under a Schottky gate, but the carrier mobility was considerably greater at all biases than predicted assuming randomly positioned donors. The depletion and mobility data for the AlAs barrier samples could only be explained by postulating the existence of a pool of electrons around the doping plane, which screened the donors to produce high mobilities in ungated samples but which could be removed by the application of gate bias. Bias cooling experiments on the AlGaAs samples showed that a proportion of the donor centres were occupied when samples with as few as 4*1016 m-2 donors were cooled without bias. The mobility data from such samples are discussed assuming correlations between the positions of these occupied donors.

The effect of growth temperature, δ-doping and barrier composition on mobilities in shallow AlGaAsGaAs two-dimensional electron gases

Abstract A series of two-dimensional electron gas (2DEG) structures have been grown with the 2DEG only 28 nm from the surface. The effects of growth temperature and δ-doping density have been investigated, and a comparison has been made between AlAs and Al 0.3 Ga 0.7 As barriers. A mobility of 340,000 cm 2 V −1 s −1 at 4 K has been measured for a shallow 2DEG with an Al 0.3 Ga 0.7 As barrier, which is the highest reported for such a structure.

Molecular-beam epitaxy growth of InGaAs–InAlAs high electron mobility transistors with enhanced electron densities and measurement of InAlAs surface potential

The electron densities in the channel of Si δ-doped InGaAs–InAlAs high electron mobility transistors grown on InP by molecular-beam epitaxy have been investigated by 1.4 K Shubnikov–de Haas (S–dH) measurements. Growth procedures have been developed that result in (i) minimized spreading of the Si δ doping, (ii) significantly improved transfer of electrons from the Si donors to the InGaAs channel, (iii) reduced parallel conduction associated with electrons remaining in the vicinity of the Si donors, and (iv) high sheet density-mobility products (nH×μH), important for a low access resistance into the channel. The Fermi energy of the free InAlAs surface has also been estimated by comparing self-consistent calculations of the channel electron density with the S–dH data from samples with progressively thinner InAlAs Schottky layers. The Fermi energy is found to be pinned at ∼0.6 eV below the conduction band edge, in agreement with the value deduced from photoreflectance spectrometry [J. S. Hwang, W. C. Hwang, ...

Charge depletion of n+-In0.53Ga0.47As potential wells by background acceptor doping

Charge depletion from 20 monolayers of n+-In0.53Ga0.47As, uniformly doped with Si donors and embedded within Be-doped In0.53Ga0.47As, has been studied at 1.2 K by magnetotransport measurements. Electron subband energies and densities associated with the n+-In0.53Ga0.47As potential well prove sensitive to the presence of the acceptors at concentrations up to 3×1016 cm−3. Agreement between the experimental data and the electronic subband structure calculated self-consistently by solving the one-dimensional Schrodinger and Poisson equations is excellent. The results suggest that intentional background acceptor doping could be a useful mechanism for tuning subband fillings and energies in potential wells formed by highly confined donors.

Surface segregation of Si in δ-doped In0.53Ga0.47As grown by molecular beam epitaxy

Abstract A study of Si spreading in δ-doped InGaAs grown lattice matched on InP by molecular beam epitaxy is reported. The layers were designed to distinguish between thermal diffusion and surface segregation as mechanisms for migration of the dopant atoms. Comparison of Shubnikov-de Haas data with self-consistent calculations shows that spreading occurs by surface segregation at substrate temperatures in the range 470–520°C and Si densities of ⩽ 4.0 × 10 12 cm −2 ; thermal diffusion is found to be negligible. A near ideal δ-doping profile can be maintained if a δ-doped layer is capped with as little as 3 monolayers of InGaAs grown at ⩽ 470°C before subsequent material is deposited at higher temperatures, up to ∼ 520°C.

Quantum transport measurements on Si δ- and slab-doped In0.53Ga0.47As grown by molecular beam epitaxy

A series of high quality δ-doped In 0.53 Ga 0.47 As samples have been grown lattice matched to InP with design doping densities in the range 2×10 12 to 5×10 12 cm -2 . Analysis of the individual sub-band densities deduced from the Shubnikov-De Haas effect shows that both spreading and amphoteric behaviour increase with doping density