T.M. Burke

The two-dimensional lateral injection in-plane laser

In this paper, a two-dimensional (2-D) p-n junction was used for population inversion in a GaAs quantum-well laser. The device, incorporating modulation doping within the core of a separate confinement heterostructure, was designed to exploit the amphoteric behavior of silicon in GaAs [doping p-type on [311]A facets and n-type on [100]]. It is believed to be the first lasing device to use an amphoterically doped junction for population inversion. In the first attempted design (described here), CW lasing was achieved at temperatures up to 90 K. The factors affecting the temperature dependence of threshold are discussed in the context of possible design improvements. The device may eventually show improved modulation bandwidth over conventional vertical injection lasers with bulk contacts, since its geometry and the 2-D nature of the injection offer reduced capacitance, HEMT integration, and an elimination of carrier capture problems.

Surface decontamination of patterned GaAs substrates for molecular beam epitaxy regrowth using a hydrogen radical source

To investigate the efficiency of hydrogen radical surface cleaning of patterned GaAs substrates, resonant tunneling devices have been fabricated in which the regrowth interface lies between the collector and the double barrier structure. Secondary-ion-mass spectroscopy data collected at the patterned substrate/regrown layer interface show a significant reduction of contaminant species after radical cleaning at ∼450 °C for 2 h. The current–voltage characteristics of the resonant tunneling device further indicate a significant improvement in the quality of the regrowth interface in comparison to that achieved by standard thermal decontamination.

Hydrogen radical surface cleaning of GaAs for MBE regrowth

Abstract Modulation-doped GaAs AlGaAs two-dimensional electron gas (2DEG) structures have been regrown on air-exposed GaAs buffer layers, at varying proximity to the regrowth interface. The degradation in 2DEG quality with decreasing separation from a hydrogen radical (H∗) cleaned regrowth interface was found to be much reduced in comparison to that for a thermally cleaned interface. H∗ cleaning has allowed for the growth of a 2DEG lying only 50 nm from the regrowth interface with a mobility, after illumination, of 5.3 × 105cm2 V− 1 s− 1 at a carrier concentration of 4.2 × 1011cm− 2. SIMS characterisation has been used to measure significant reductions in contamination at the regrowth interface at cleaning temperatures of 500°C. Cathodoluminescence data, measured for a 5 nm quantum well lying 30 nm from the regrowth interface, further indicate the improved growth morphology achieved following H∗ cleaning, in comparison to that achieved by thermal decontamination.

Variation of the confinement potential of a quasi‐one‐dimensional electron gas by lateral p‐n junctions

We present the first study of a new system where the confinement potential of a high mobility quasi‐one‐dimensional electron gas on the (100) GaAs surface is varied using two, two‐dimensional hole gases produced on the adjacent (311)A surfaces. The structure consists of two lateral two‐dimensional p‐n junctions, placed back‐to‐back to form a p‐n‐p structure. The confinement potential of the narrow n‐type channel can thus be modulated by applying a bias to the adjacent p‐type regions. Magnetoresistance measurements of the narrow channel show magnetic depopulation of the one‐dimensional subbands [K.‐F. Berggren, T. J. Thornton, D. J. Newson, and M. Pepper, Phys. Rev. Lett. 57, 1769 (1986)], following the model of Berggren et al. [Phys. Rev. B 37, 10118 (1988)] widths and one‐dimensional carrier concentrations are extracted to fully characterize the dependence of the channel on the applied ‘‘hole‐gate’’ voltage.

Far‐infrared study of a quasi‐one‐dimensional electron gas formed on (100)GaAs facets with hole gas sidegates on a (311)A GaAs substrate

A new type of quasi‐one‐dimensional electron gas has been realized by using molecular beam epitaxy to grow a high mobility heterostructure on a (311)A GaAs substrate selectively etched to expose (100) facets. The electron gas formed on the (100) facets is confined in one lateral dimension by the p–n junctions formed with the adjacent two‐dimensional hole gases on (311)A, thereby forming a p–n–p structure. Far‐infrared cyclotron resonance spectra demonstrate the dimensionality of such structures and yield typical lateral confinement energies of 22.3 cm−1 and electronic widths of ∼900 nm. These estimates are supported by cathodoluminescence data.

Mobility (106 cm2 V−1 s−1) of 2DEGs, 30 nm from ex situ patterned GaAs regrowth interfaces

Abstract We have regrown, on ex situ patterned GaAs substrates, using hydrogen radical decontamination, two-dimensional electron gases (2DEGs) confined in 15 nm quantum wells (QWs) with the inverted AlGaAs/GaAs interface 30 nm from the regrowth interface (RI), which conduct before illumination at 1.5 K. Mobilities in excess of 1×10 6 cm 2 V −1 s −1 have been achieved. We have not observed a degradation in the mobility for a constant carrier concentration between 2DEGs, 200 and 30 nm from the RI. A control structure with the 2DEG 30 nm from the RI was also grown on an un-patterned GaAs substrate that was only thermally cleaned, which had a maximum mobility of 3×10 4 cm 2 V −1 s −1 after illumination at 1.5 K.

Tunable, Strongly Non parabolic Confinement in a Quasi-One-Dimensional Electron Gas Formed by Epitaxial Regrowth.

A new type of quasi-one-dimensional electron gas (Q1DEG) characterised by a tunable, strongly non parabolic confining potential in the lateral direction has been produced, using molecular beam epitaxy to grow a high-mobility heterostructure on a (311)A GaAs substrate selectively etched to expose (100) facets. The electron gas on the (100) facets is confined in one dimension by the two-dimensional hole gases on the (311)A facets, forming a p-n-p structure. Infrared cyclotron resonance (CR), magneto resistance and electron-beam-induced current (EBIC) measurements have been made on these Q1DEGs for various biases (Vh) between the hole and electron gases to investigate its effects on the confinement potential. Two different regimes are present. For Vh>-1.9 V, a strong peak attributable to a confined magnetoplasmon (CPM), together with its higher-frequency harmonics, are observed in the CR spectra. For Vh<-1.9 V, a new mode appears and the CPM no longer fits the experimental data. The anomalous dependence of the resonance frequency on carrier density, together with the EBIC images, provides some understanding of the tunable, non parabolic nature of the confining potential.

Hydrogen radical cleaning and low energy electron stimulated desorption of surface contaminants for MBE regrowth of GaAs

Abstract Modulation doped two-dimensional electron gas (2DEG) samples have been used to characterise the quality of epitaxial growth achieved within 400Aof a hydrogen radical (H * ) cleaned GaAs regrowth interface. For planar ex-vacuo exposed substrates, regrowth of a high quality InGaAs/GaAs pseudomorphic 2DEG has been achieved at only 125Afrom the cleaned interface. For patterned substrates, a GaAs/AlGaAs modulation doped 2DEG with a 1.5 K, dark mobility of 1 × 10 6 cm 2 V −1 s −1 at a carrier concentration of 8 × 10 11 cm −2 has been regrown at a separation of 375 A after H * cleaning at 500°C. These results highlight the improved growth morphology which occurs following H * cleaning of the regrowth interface in comparison to that achieved using standard thermal decontamination. Static SIMS analysis shows that low energy electron irradiation at an energy of 100 eV may also be used as an alternative non-destructive method for contaminant reduction at an air exposed GaAs(100) surface.

One-dimensional electron transport in devices fabricated by MBE regrowth over a patterned δ-doped backgate

Abstract MBE regrowth and hydrogen radical decontamination of an ex situ patterned GaAs wafer have been successfully used to create a one-dimensional constriction which exhibits quantised ballistic conductance. Deviations from exact quantisation are discussed in terms of electron reflection at the entrance to the constriction.

Desorption of organic species from the GaAs (100) surface at low temperatures using low energy electron irradiation in a hydrogen ambient

We present a technique for the controlled removal of organic adsorbates from the GaAs (100) surface incorporating hydrogen dosing (atomic or molecular) combined with low-energy electron irradiation. High-resolution electron energy-loss and Auger electron spectroscopes verify a considerable desorption of carbon/hydrocarbons following electron irradiation at 50 eV under a hydrogen atom flux even at room temperature. At a sample temperature of 500 °C, static secondary ion mass spectroscopy data demonstrate selective area removal of carbon from the surface following 25 eV electron irradiation in a molecular hydrogen ambient, with a desorption rate controlled by the incident electron flux.