G Hill

Resonant magnetotunnelling of electrons and holes in a p-i-n diode device incorporating a double barrier structure

The authors observe resonant tunnelling of electrons and holes in a GaAs p-i-n diode incorporating two AlAs barriers in the undoped region. Peaks due to the HH1, LH1, E1 and HH2 (E=electron, LH=light hole, HH=heavy hole) resonances are observed, in that order of increasing voltage. The voltage separation of the LH1 and E1 resonance is significantly larger than expected from a simple quantum mechanical model due to an interaction effect involving resonant buildup of electron space charge in the quantum well. High magnetic fields B//J and B perpendicular to J are used to investigate the device and confirm the assignment of the resonances.

Tunneling and magneto-tunnelling effects in n+GaAs/(AlGa)As/n-GaAs/n+GaAs devices

Oscillatory stuctures recently reported by Hickmott et al. (1984) in the I-V characteristics of n+GaAs/(AlGa)As/n-GaAs/n+GaAs tunnelling devices are observed at zero magnetic field and temperatures up to 50K, demonstrating that neutralisation of donors by magnetic freeze-out in the n-GaAs layer is not required to observe the structure.

Photoluminescence of donor energy levels in resonant tunnelling devices

Photoluminescence spectroscopy is used to investigate the donor-assisted resonant tunnelling processes in double-barrier structures which incorporate a low-density delta -doped donor layer in the centre of the quantum well. A quantum well luminescence line corresponding to hole-neutral donor recombination is observed, along with two other lines at higher photon energy. The possible origin of these two lines is discussed.

Molecular beam epitaxy growth of GaAs/AlAs double-barrier resonant tunnelling devices on (311)A substrates

The authors investigate resonant tunnelling in p-type silicon-doped GaAs/AlAs double-barrier quantum well structures grown by molecular beam epitaxy on the (311)A GaAs surface. Their current-voltage characteristics compare favourably with structures grown on the conventional (100) orientation using beryllium as the acceptor.

High-magnetic-field studies of hole energy dispersion, cubic anisotropy and space charge build-up in the quantum well of p-type resonant tunnelling devices

Magnetic fields up to 41 T (B perpendicular to J) are used to investigate hole tunnelling in p-type double-barrier AlAs/GaAs structures and to probe the dispersion curves of the hole states of the quantum well. The high magnetic fields reveal the cubic anisotropy of these states. A detailed comparison is made between the experimental data and the theoretical hole dispersion curves. Hole space charge build-up is observed in the quantum well and is measured using the Landau quantization effect for B//J.

Possible Wigner solid phase transitions in a series of high-carrier-density two-dimensional hole gases

Transport measurements on a series of high-mobility, high-carrier-density (1.0*1011<or=ns<or=1.6*1011 cm-2) 2D hole systems in fields up to 30 T and temperatures down to 30 mK show transitions into a very-high-resistance state at a range of Landau level filling factors ( nu ) near 2/7. The insulating state shows clear voltage threshold behaviour and strong temperature dependence consistent with a strongly pinned Wigner solid. The authors also present measurements on a gated 2D hole gas which enabled the systematic variation of the carrier density near the Wigner solid phase boundary.

Modulated blue shift of the quantum well electroluminescence in a GaAs/AlAs superlattice resonant tunnelling device

Abstract Electrical transport and electroluminescence measurements have been performed on a p - i - n superlattice resonant tunnelling device with a narrow 3.1 nm quantum well in the centre. The electroluminescence observed from the centre quantum well blue shifts with increasing electric field. The application of a magnetic field perpendicular to the layers modulates the blue shift of the quantum well recombination. Possible physical origins for the blue shift are discussed.

Measurement of the anisotropy of the hole dispersion curves in an AlAs/GaAs/AlAs quantum well grown on a (311)A orientated substrate

Continuous magnetic fields applied parallel to layer interfaces are used to examine the in-plane energy dispersion and anisotropy of the quantum well states of double barrier AlAs/GaAs resonant tunnelling diodes. The devices are grown on substrates with different orientations using molecular beam epitaxy. Measurements on a device grown on a (311)A substrate reveal the pronounced biaxial symmetry of the confined hole states in a quantum well of this orientation, including a marked saddle-shaped structure for one of the subbands. The spectra are compared with those of similar devices grown on a (100) surface.

Quantum well luminescence due to minority photoelectrons in p-type resonant tunnelling structures

Photoluminescence spectroscopy is used to investigate p-type double-barrier resonant tunnelling structures based on GaAs/AlAs. Strong photoluminescence from the quantum well is observed due to recombination of resonantly tunnelling holes with minority photogenerated electrons, which also tunnel into the quantum well. The luminescence undergoes a red shift with increasing bias and its intensity shows peaks at biases corresponding to the first four hole resonances in the current-voltage characteristics. Two additional strong peaks are also seen in this intensity-bias plot, due to electron resonant tunnelling.

Observation of a spin polarization phase transition of the 4/3 fractional quantum Hall state in a high-mobility 2D hole system

We report the observation of a spin polarization phase transition of the 4/3 fractional quantum hall state of a high-mobility 2D hole system in a GaAs-(Ga, Al)As heterostructure. Mobilities in excess of 1000000 cm2 V-1 s-1 are achieved at a density of 0.86 * 1011 cm-2. The depth of the 4/3 minimum is seen to weaken as the carrier density is increased before disappearing completely. Upon further increase in carrier density the 4/3 minimum is re-entrant and proceeds to strengthen. The 8/3 and 7/3 states are observed to show apparently anomalous behaviour.