Low‐temperature current–voltage characteristics of n‐type GaAs/GaAlAs quantum wells delta‐doped in GaAs channel with Be acceptors are studied in the presence of a magnetic field. Negatively charged acceptor ions localize 2D conduction electrons by a combined effect of a quantum well and magnetic field parallel to the growth direction. In acceptor‐doped samples, the Hall electric field plays the role of the gate voltage. It is shown that at magnetic fields as weak as 1.5 T (or higher), the drain current reaches a constant value independent of the drain voltage. This phenomenon is due to the electron localization resulting in the decrease of conducting electron density in the crossed‐field configuration. The above special behavior of acceptor‐doped GaAs/GaAlAs heterostructures is exploited to realize a device called Magnetic‐TEGFET (Magnetic Two‐dimensional Electron Gas Field Effect Transistor) operating at low temperatures. The elimination of the gate in the studied transistor suppresses the gate‐to‐drain leakage current, which, in the standard TEGFETs, results in the electronic shot noise.

le M-TEGFET, est un nouveau type de transistor, sans grille, fonctionnant grâce à un effet magnétique.

We study experimentally low-temperature current-voltage characteristics of n-type GaAs/GaAlAs modulation doped quantum wells under the influence of an external magnetic field. In particular, we use samples doped additionally in the well with Be acceptors. As showed previously, negatively charged acceptor ions can localize conduction electrons by a joint effect of a quantum well and an external magnetic field. It is found that, in the acceptor-doped samples, the Hall field resulting from the presence of magnetic field plays the role of gate voltage. At sufficiently high magnetic fields the drain current has a constant value independent of the drain voltage. It is argued that the above phenomenon is due to the electron localization with the resulting decrease of conducting electron density in the crossed-field configuration. We propose to exploit the observed unusual behaviour as a new device called “magnetic two-dimensional field effect transistor” (M-TEGFET) operating at low temperatures.

voir abstract

We review magneto-optical and magneto-transport effects in GaAs/GaAlAs heterostructures doped in GaAlAs barriers with donors, providing two-dimensional (2D) electron gas (2DEG) in GaAs quantum wells (QWS), and additionally doped with smaller amounts of acceptors (mostly Be atoms) in the vicinity of 2DEG. One may also deal with residual acceptors (mostly C atoms). The behavior of such systems in the presence of a magnetic field differs appreciably from those doped in the vicinity of 2DEG with donors. Three subjects related to the acceptor-doped heterostructures are considered. First is the problem of bound states of conduction electrons confined to the vicinity of negatively charged acceptors by the joint effect of a QW and an external magnetic field parallel to the growth direction. A variational theory of such states is presented, demonstrating that an electron turning around a repulsive center has discrete energies above the corresponding Landau levels. Experimental evidence for the discrete electron energies comes from the work on interband photo-magneto-luminescence, intraband cyclotron resonance and quantum magneto-transport (the Quantum Hall and Shubnikov–de Haas effects). An electron rain-down effect at weak electric fields and a boil-off effect at strong electric fields are introduced. It is demonstrated, both theoretically and experimentally, that a negatively charged acceptor can localize more than one electron. The second subject describes experiment and theory of asymmetric quantized Hall and Shubnikov–de Haas plateaus in acceptor-doped GaAs/GaAlAs heterostructures. It is shown that the main features of the plateau asymmetry can be attributed to asymmetric density of Landau states in the presence of acceptors. However, at high magnetic fields, the rain-down effect is also at work. The third subject deals with the so-called disorder modes (DMs) in the cyclotron resonance of conduction electrons. The DMs originate from random distributions of negatively charged acceptor ions whose potentials provide effective QWs trapping the conduction electrons. This results in an upward energy shift of the DM as compared to the cyclotron resonance. Theory and experimental characteristics of DMs are discussed. A similarity between acceptor-doped heterostructures and 2D systems with antidots is briefly described. In conclusion, we mention weaker points in the research on acceptor-doped heterostructures and indicate possible subjects for further investigation. An effort has been made to quote all important works on the subject.

A variational theory is presented of A1− and A2− centers, i.e., of a negative acceptor ion localizing one and two conduction electrons, respectively, in a GaAs/GaAlAs quantum well in the presence of a magnetic field parallel to the growth direction. A combined effect of the well and magnetic field confines conduction electrons to the proximity of the ion, resulting in discrete repulsive energies above the corresponding Landau levels. The theory is motivated by our experimental magnetotransport results which indicate that, in a heterostructure doped in the GaAs well with Be acceptors, one observes a boil-off effect in which the conduction electrons in the crossed-field configuration are pushed by the Hall electric field from the delocalized Landau states to the localized acceptor states and cease to conduct. A detailed analysis of the transport data shows that, at high magnetic fields, there are almost no conducting electrons left in the sample. It is concluded that one negative acceptor ion localizes up to four conduction electrons.

We demonstrate theoretically that bound acceptors states of a two dimensional electron gas in quantizing magnetic field can localize two electrons on a same site. We calculate the energies and wave functions of the second quantum state, and show that they are close to calculations of the first quantum state found previously.