R. K. Hayden

Hole space‐charge buildup and evidence for sequential tunneling in p‐type double‐barrier resonant tunneling devices

Magnetoquantum oscillations in the tunnel current of a p‐type double‐barrier AlAs/GaAs/AlAs device are used to measure the buildup of hole space charge in the quantum well over a wide range of bias. These measurements demonstrate sequential tunneling of holes. The effective mass for hole tunneling is estimated.

Resonant magnetotunnelling spectroscopy : a direct probe of the complicated dispersion curves and negative mass behaviour of holes confined in a quantum well

Abstract We describe a novel magnetotunnelling spectroscopy technique for probing the complicated dispersion curves of hole states in the quantum well of p-type double barrier resonant tunnelling structures. Strong mixing between light and heavy hole states is observed. Some of the states clearly exhibit negative hole effective mass for motion in the plane of the quantum well. The results are contrasted with the simple case of resonant tunnelling of electrons in in-plane and tilted magnetic fields. For electron resonant tunnelling in tilted fields, we observe additional peaks in I ( V ). These are due to non-Landau level index-conserving transitions from the two-dimensional emitter accumulation layer to the quantum well.

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.

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.

Investigating the cubic anisotropy of the confined hole subbands of an AlAs/GaAs/AlAs quantum well using resonant magnetotunneling spectroscopy

The energy‐wave‐vector dispersion curves and cubic anisotropy of the confined hole subbands of a (001) AlAs/GaAs/AlAs valence‐band quantum well are studied in resonant magnetotunneling experiments using pulsed magnetic fields up to 41 T. The experimental results are compared with calculations using a six‐band model which includes the effect of the finite electric field in the quantum well. The comparison convincingly demonstrates that the technique is sufficiently accurate to measure fine details of the band structure of the valence‐band quantum well.

Linewidth broadening of excitonic luminescence from quantum wells in pulsed magnetic fields

Abstract We investigate the effect of magnetic fields, B, up to 42 T , on the photoluminescence spectra of In0.5Ga0.5As/GaAs single quantum wells (QWs). We find that the full-width at half-maximum, W, of the excitonic recombination spectrum increases significantly at these high fields to an extent depending on the direction of B. The increase of W with magnetic field is due to the squeezing of the exciton wave function, which increases the effect of the QW potential energy fluctuations on the line width. A statistical model for the QW interface disorder is used to explain these results. In turn, this allows us to probe the magnetic field dependence of the spatial extent of the exciton in the QW.

Growth and characterization of p-type GaAs(AlGa) As heterostructures grown on high-index GaAs surfaces

Abstract We have investigated a series of Be-doped GaAs (AlGa) As two-dimensional hole gas (2DHG) structures grown on (110)-, (111)B-, (211)B- and (311)B-orientated substrates and compare their properties with high-mobility samples grown on (311) A using Si doping. The samples were prepared and grown under the same conditions so as to render them comparable. They are found to have mobilities which are strongly anisotropic within the plane. The highest mobility, ∼ 100 000 cm2V−1s−1, for the Be-doped samples is found on the (110) surface while the (211) surface gave the lowest values, ∼ 10 000 cm2V−1s−1. However, the latter samples are found to have quantum Hall effect critical currents of > 70 μA, an exceptionally high value for a hole gas which makes them suitable for metrology. All the samples show strong low-field positive magnetoresistance with resistance increases of up to 30% at magnetic fields of only 0.1 T. The presence of this feature on all the different planes shows that it does not depend upon the details of the band structure. It is identified with the lifting of the degeneracy of the spin sub-bands by the asymmetrical potential giving rise to a classical two-band magnetoresistance. The modulation-doped GaAs (AlGa) As heterostructures on the (311) A GaAs surface using silicon as the acceptor produced 2DHGs with a low-temperature hole mobility exceeding 1.2 × 106 cm2 V−1 s−1 at carrier concentrations as low as 0.8 × 1011 cm−2. This hole mobility is the highest ever observed at such low densities by any growth technique. These 2DHG samples show for the first time the persistent photoconductivity effect. This effect is normally absent in 2DHG systems. An analysis of the number density and temperature dependence of the mobility leads us to conclude that the mobility is limited by phonon scattering above ~ 4 K and by interface scattering at lower temperatures. Continuous magnetic fields applied parallel to layer interfaces are used to examine the in-plane energy dispersion and anisotropy of the quantum well states in p-type silicon-doped double-barrier GaAs AlAs resonant tunnelling structures grown on the (311) A GaAs surface. Measurements reveal that the lowest subband is isotropic at low energies. This indicates that atomic layer corrugations may be important in determining the mobility of hole heterostructure devices grown on non-(100)-oriented surfaces.

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.

The transition to chaos in a wide quantum well

Abstract Experimental and theoretical studies of electron transport in a resonant tunnelling diode with a tilted magnetic field are reported. We map the transition to chaotic dynamics for electrons injected into the potential well from an emitter accumulation layer. In the regime of mixed stable-chaotic electron dynamics, we have identified a stable-orbit trifurcation that leads to a sudden three-fold reduction in the voltage spacing of resonant peaks in the calculated and measured current–voltage curves. We explain this effect by considering how the dynamical properties of the stable orbits affect the quantized states of the potential well.