Fundamental studies and device application of δ-doping in GaAs Layers and in Al_xGa_1−xAs/GaAs heterostructures

Abstract

In addition to the realization of atomically abrupt interfaces in III–V semiconductors by molecular beam epitaxy, the confinement of donor and acceptor impurities to an atomic plane normal to the crystal growth direction, calledδ-doping, is important for the fabrication of artifically layered semiconductor structures. The implementation ofδ-function-like doping profiles by using Si donors and Be acceptors generates V-shaped potential wells in GaAs and Al_xGa_1−xAs with a quasi-two-dimensional (2D) electron (or hole) gas. In this review we define three areas of fundamental and device aspects associated withδ-doping. (i) The prototype structure ofδ-doping formed by a single atomic plane of Si donors in GaAs allows to study the 2D electron gas by magnetotransport and tunneling experiments, to study the metal-insulator transition, and to study central-cell and multivalley effects. In addition, non-alloyed ohmic contacts to GaAs and GaAs field-effect transistors (δ-FETs) with a buried 2D channel of high carrier density can be fabricated fromδ-doped material. (ii) GaAs sawtooth doping superlattices, consisting of a periodic sequence of alternating n- and p-typeδ-doping layers equally spaced by undoped regions, emit light of high intensity at wavelengths of 0.9 <λ <1.2 [μm], which is attractive for application in photonic devices. The observed carrier transport normal to the layers due to tunneling indicates the feasibility of this superlattice as effective-mass filter. (iii) The confinement of donors (or acceptors) to an atomic (001) plane in selectively doped Al_xGa_1−xAs/GaAs heterostructures leads to very high mobilities, to high 2D carrier densities, and to a reduction of the undesired persistent photo-conductivity. Theseδ-doped heterostructures are thus important for application in transistors with improved current driving capabilities.