Coulomb drag is a transport phenomenon whereby long-range Coulomb interaction between charge carriers in two closely spaced but electrically isolated conductors induces a voltage (or, in a closed circuit, a current) in one of the conductors when an electrical current is passed through the other The magnitude of the effect depends on the exact nature of the charge carriers and microscopic, many-body structure of the electronic systems in the two conductors Drag measurements have become part of the standard toolbox in condensed matter physics that can be used to study fundamental properties of diverse physical systems including semiconductor heterostructures, graphene, quantum wires, quantum dots, and optical cavities

Coulomb drag

We implement metallic layers of Si-doped (110) GaAs as modulation doping in high mobility p-type heterostructures, changing to p-growth conditions for the doping layer alone. The strongly autocompensated doping is characterized in bulk samples first, identifying the metal-insulator transition density and confirming classic hopping conduction in the insulating regime. To overcome the poor morphology inherent to Si p-type (110) growth, heterostructures are then fabricated with only the modulation-doping layer grown under p-type conditions. Such heterostructures show a hole mobility of μ=1.75×105cm2∕Vs at density p=2.4×1011cm−2. We identify the zero-field spin-splitting characteristic of p-type heterostructures, but observe a remarkably isotropic mobility and a persistent photoconductivity unusual for p heterojunctions grown on other facets. This modulated growth technique is particularly relevant for p-type cleaved-edge overgrowth and for III-V growth chambers, where Si is the only dopant.

Modulating the growth conditions: Si as an acceptor in (110) GaAs for high mobility p-type heterostructures

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Si as an acceptor in (110) GaAs for high mobility p-type heterostructures

Mesure de l'effet Hall dans des conditions ou la conduction par sauts d'impuretes est le mecanisme dominant. On ne detecte pas l'effet Hall du a ce type de conduction, et determine une limite superieure de 1,7×10 −13 (Ω,cm) −1 pour la conductivite de Hall dans les conditions de l'experience. Cette valeur est 37 fois plus faible que celle predite par la theorie d'Holstein

A Investigation of the Hall Effect in Impurity Hopping Conduction.

Photoluminescence (PL) spectra of beryllium δ-doped GaAs∕AlAs multiple quantum wells are studied over a range of doping concentrations. Possible mechanisms for carrier recombination, both above and below the Mott metal-insulator transition, are discussed. In 15nm width Be δ-doped GaAs∕AlAs quantum wells, it is found that the Mott transition can be observed if the acceptor concentration (NBe)⩾3×1012cm−2. At doping concentrations near the Mott transition band the PL spectra are dominated by excitons-bound-to-acceptor impurity recombinations. Above the Mott transition, the radiative recombination of free electrons with a two-dimensional hole gas is found to be the dominant recombination mechanism.

Radiative recombination spectra of p-type δ-doped GaAs∕AlAs multiple quantum wells near the Mott transition

Thermally activated intersubband and hopping transport in center-doped p-type GaAs/AlxGa1-xAs quantum wells.

We derive an expression for the contribution to the resistivity from the carrier - carrier scattering between two subbands with different masses in a single quantum well. The effects of the true wave functions of the carriers in the direction normal to the quantum well are taken into account. The calculations are done within the generalized Drude approach and with the RPA screening matrix. Numerical results for general temperatures are presented for a p-type centre-doped GaAs quantum well and compared with experiments.

Current drag in a single quantum well

We present an expression for the impurity resistivity for a general number of subbands in singly and doubly δ-doped structures. The true wave functions of the carriers and the intraband scattering from interaction between carriers of different bands are considered. The calculations are performed within the generalized Drude approach and with the temperature dependent RPA screening matrix. Numerical results for general temperatures are presented for singly n-doped Si and doubly n-doped Si with varying distance between the doped layers. We propose an explanation for the observed enhancement of the mobility in doubly δ-doped structures, as compared to singly δ-doped systems.

E Söderström

Papers

Thermally activated intersubband and hopping transport in center-doped p-type GaAs/AlxGa1-xAs quantum wells.

Current drag in a single quantum well

Impurity resistivity in doubly δ-doped systems