Search Results - (Author, Cooperation:L. Eaves)

2012-02-04

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2018-05-16

National Academy of Sciences

0027-8424

1091-6490

Biology

Medicine

Natural Sciences in General

1089-7550

AIP Digital Archive

Physics

We investigate electron tunneling through GaAs/(AlGa)As/GaAs, single-barrier tunnel diodes in which a layer of self-assembled InAs quantum dots is incorporated onto the center plane of the (AlGa)As tunnel barrier. We study the effect on the electrical conduction of substrate orientation and of the inclusion of thin GaAs cladding layers on either side of the dot layer. We find that the presence of the cladding layers increases the conduction. We attribute this to a raising of the energy of the electron states, probably due to the diffusion of Ga into the dots. Photoluminescence measurements confirm this hypothesis. We show that this effect can be used to tailor the transport characteristics for specific applications. © 2002 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We investigate the optical and electrical properties of n-i-n GaAs/(AlGa)As double barrier resonant tunneling diodes (RTDs) in which a layer of InAs self-assembled quantum dots (QDs) is embedded in the center of the GaAs quantum well. A combination of photoluminescence (PL) and electrical measurements indicates that the electronic states and charge distribution in this type of RTD are strongly affected by the presence of the dots. Also, the dot PL properties depend strongly on bias, being affected by tunneling of majority (electrons) and minority (photocreated holes) carriers through the well. The measurements demonstrate nonlinear effects in the QD PL by means of resonant tunneling and the possibility of using the dot PL as a probe of carrier dynamics in RTDs. © 2000 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We investigate indium interdiffusion in InAs/(AlGa)As self-assembled quantum dots by studying the changes in the optical properties of the system induced by ion implantation and/or thermal annealing. Interdiffusion of In–Ga and In–Al atoms at the interface between the dot and the (AlGa)As barrier takes place in as-grown samples and is enhanced by the postgrowth treatments. In contrast to the proposed interdiffusion as the way for suppressing the optical emission from the wetting layer, we show that it drives the system towards a predominantly two-dimensional morphology. © 2001 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

The thermal behavior of lasers based on In0.5Ga0.5/As/GaAs self-aggregated quantum dots is investigated. Increasing temperature from 10 to 290 K produces a narrowing of the dot laser mode distribution. This effect is explained in terms of carrier relaxation between dots and carrier thermal escape from dots to nonradiative recombination centers. The thermal dependence of the threshold current and the differential quantum efficiency is also discussed. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Electroluminescence (EL) due to impact ionization in the high field region of a double-barrier resonant tunneling structure is reported. Knowledge of the charge distribution in the structure enables a detailed analysis to be made of the impact ionization rate as a function of electric field. Large peak-to-valley ratios of 15:1 in the EL emission intensity from the quantum well active region are observed.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Capacitance–voltage characteristics have been measured at various frequencies and temperatures for structures containing a sheet of self-assembled InAs quantum dots in both n-GaAs and p-GaAs matrices. Analysis of the capacitance–voltage characteristics shows that the deposition of 1.7 ML of InAs forms quantum dots with electron levels 80 meV below the bottom of the GaAs conduction band and two heavy-hole levels at 100 and 170 meV above the top of the GaAs valence band. The carrier energy levels agree very well with the recombination energies obtained from photoluminescence spectra. © 1998 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Magnetoquantum oscillations in the tunnel current of double-barrier n-GaAs/(AlGa)As/GaAs/(AlGa)As/GaAs resonant tunneling devices reveal evidence of sequential tunneling in the voltage range corresponding to the resonance when electrons tunnel into the second subband of the GaAs quantum well. The sequential tunneling arises from intersubband scattering between two quasi-bound states of the well. Near this resonance, the charge buildup in the well can be estimated from the magnetoquantum oscillations.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We investigate the electroluminescence spectra of edge-emitting lasers having self-assembled quantum dots as the active medium. A broad laser emission is observed with a modulation of intensity corresponding to single or bunches (supermodes) of Fabry–Pérot modes. The variation of the laser spectra with magnetic field shows that the supermodes originate from laser cavity effects and are not related directly to the electronic properties of the quantum dots. Measurements taken on devices of different cavity height, length, and lateral width indicate that the important parameter controlling the laser multimode emission is the cavity height, effectively the substrate thickness. In particular, the period of the supermodes is inversely proportional to this thickness, indicating that the modulation of the laser emission intensity is due to the leakage of modes into the transparent substrate. © 2000 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A new technique has been developed to probe the region of apparent bistability due to a tunneling resonance in the characteristic of a semiconductor asymmetric double-barrier structure. The measuring circuit uses a voltage supply designed to have a load line with positive slope, equivalent to a voltage source and negative series resistance. The appearance of bistability and hysteresis in the characteristic is an artifact of the conventional measuring technique, which employs a load line with negative slope. The complete characteristic is found to be a continuous Z-shaped curve between 50 and 150 K, corresponding to tristability. Equivalent circuit models for the device and voltage supply predict a narrow range of circuit parameters for which a static operating point exists inside the tristable region.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have investigated the current-voltage [I(V)] characteristics of a gated GaAs/(AlGa)As resonant tunneling diode. As the negative gate voltage is progressively increased I(V) becomes asymmetric. In particular the peak-to-valley ratio in forward bias is decreased from (approximately-equal-to)20 to (approximately-equal-to)1, but in reverse bias remains constant (approximately-equal-to)20. This arises from a lateral variation of the voltage drop across the emitter tunnel barrier, which in forward bias leads to a smearing of the resonance. We discuss the relationship between our experiment and the low peak-to-valley ratios of two-terminal submicron resonant tunneling diodes observed by other groups.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The persistent photoconductivity effect at low temperatures and under hydrostatic pressure is used to study the effect of spatial correlation of DX centers on the mobility and Shubnikov–de Haas oscillations in heavily doped n-type GaAs. Upon illumination, the transport mobility and the quantum relaxation time τs decrease rapidly with increasing carrier concentration. This is due to the destruction of the correlated distribution of DX centers by the random photoionization process. The enhancement of τs due to correlations is estimated.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

A new process based on photolithography and selective wet etching has been used to fabricate small area resonant tunnelling diodes. The low-temperature current-voltage (I-V) characteristics of diodes with conducting widths less than 0.1 μm show additional peaks due to 1D lateral quantum confinement. We observe a pronounced asymmetry in I-V which we explain in terms of tunnelling from emitter states which have a different degree of lateral quantum confinement.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

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.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

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.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have fabricated GaAs/AlAs p-i-n double-barrier resonant tunneling diodes with lateral dimensions down to 0.5 μm. There are significant differences in the electroluminescence spectra of these diodes as compared with large area diodes fabricated from the same heterostructure. In particular, a red shift of the quantum well emission line is observed together with an additional spectral line which is attributed to spatially indirect recombination. Furthermore, there is a strong increase in the low-temperature electroluminescence efficiency for the smallest devices. © 1994 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We demonstrate that it is possible to observe transport through individual tunneling channels due to zero-dimensional states in large area resonant tunneling devices (RTD). These localized states are found to be related to the presence of donor impurities in the vicinity of the quantum well but their binding energies are larger than that due to a single isolated hydrogenic donor. The states give rise to additional peaks in current voltage below the threshold for the main resonant peak. These peaks are visible in RTD with essentially any lateral dimension provided the current is measured with sufficient sensitivity.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Oscillatory structure in the low-temperature current-voltage characteristics of Be-doped p-type GaAs/(AlGa)As/GaAs single barrier tunneling devices is observed. The oscillations have period ΔV=39 mV, close to (h-dash-bar)ωL/e, where (h-dash-bar)ωL is the longitudinal optic (LO) phonon energy in GaAs. They result from energy relaxation of hot holes injected through the tunnel barrier. The oscillatory amplitude varies as exp(Ea/2kT), where Ea is the ionization energy of the Be acceptors.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

We have studied the optical properties of (InGa)As self-assembled quantum dots grown on (311)B-oriented GaAs substrates. The luminescence linewidth is considerably narrower than that of similar samples grown on (100). The difference is explained in terms of the in-plane coupling of dots which is more significant in (311)B. In order to assess the device potential of (311)B (InGa)As dots, we have studied the properties of edge emitting lasers by extending the well-known technology for (100) to the (311)B devices. © 1998 American Institute of Physics.

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