J. R. A. Cleaver

Electrically pumped single-photon sources in lateral p-i-n junctions

Electrically pumped single-photon sources using semiconductor quantum dots are of interest as they can be integrated with other semiconductor devices, using standard processing techniques. In this letter, we report electroluminescence from single quantum dots in a lateral p-i-n junction. Exciton and biexciton emission from a single quantum dot can be achieved under different electrical bias conditions. Antibunching effects from exciton and biexciton emission are observed using cw and pulsed electrical injection, indicating single-photon emission; this can be used for quantum information processing.

Ultralow‐energy focused electron beam induced deposition

We have studied focused electron beam induced deposition from W(CO)6 at beam primary energies between 20 and 0.06 keV. Submicrometer resolution with 4 nA beam current was maintained at very low primary energies using a retarding field configuration. Decomposition cross sections of W(CO)6 for primary energies below about 1 keV were found to be about a factor of 4 larger than those at 20 keV. Depending on the scan conditions, the resistivity of the deposits formed using low primary energies was found to be up to about a factor of 4 lower than at 20 keV implying a higher metallic content. These results form the basis of an improved method for repairing clear defects on x‐ray masks and for making conducting tracks on semiconducting materials.

Electrical resistance of electron beam induced deposits from tungsten hexacarbonyl

We studied the change in electrical conductivity of deposits from focused electron beam induced dissociation of W(CO)6 for different exposure conditions. Lines were deposited by scanning repeatedly to build up the same total electron dose; with different electron doses per scan, resistance differences of more than one order of magnitude resulted. The lines with lower deposited thicknesses also have lower resistances, and so cannot be explained in terms of constant resistivity and different cross‐sectional areas. A theoretical description involving an intermediate and a final product is proposed and compared to the experimental results.

Gas-assisted focused ion beam etching for microfabrication and inspection

Abstract A focused ion beam system has been applied to the etching of semiconductor materials. The etching can be carried out by sputtering with the ion beam alone or by a combination of the ion beam and a reactive gas, in this case chlorine. The flexibility of the system allows beam currents from 5.10 -7 to 5.10 -12 A to be used, with a typical beam current density of 1–2 A.cm -2 . A number of diverse applications that make use of the large current range available have been identified and characterised in the system. These range from large-area layer removal and TEM specimen preparation with high beam currents to the formation of fine, smooth features using small-diameter, low-current ion probes.

Focused ion beam repair techniques for clear and opaque defects in masks

Abstract Focused ion beam processes for the repair of both opaque and clear defects in chromium-on-glass mask plates are considered, and a novel process for the deposition of opaque carbon films for the repair of clear defects is described and compared with the use of light-scattering grating structures sputtered into the glass. An ion-beam mask repair system is described.

Near-infrared to visible up-conversion in a forward-biased Schottky diode with a p-doped channel

Near-infrared radiation of wavelength 1.5 μm is up-converted to a visible wavelength of 818 nm by internal photoemission in a Schottky diode with a modulation p-doped channel. The near-infrared light incident upon the metal–semiconductor interface excites electrons from the metal into the semiconductor. The electrons then drift into the quantum well where they recombine radiatively, producing luminescence at the shorter wavelength of 818 nm. The intensity of the luminescence is strongly dependent on bias, and turns on at a forward bias of −0.7 V.

Fabrication and performance of GaAs MESFETs with graded channel doping using focused ion-beam implantation

The dopant concentration in the channel region of GaAs MESFETs is tailored by focused ion-beam implantation, allowing the fabrication of devices with higher power ratings than uniformly doped devices of similar dimensions. With this technique, multiple masking steps during fabrication and avoided, and dopant concentration can be changed with great precision in both position and magnitude. The effect of dopant grading on other device parameters, such as the transconductance and the pinch-off voltage, is reported.<<ETX>>

Ultrafast characterization of an in‐plane gate transistor integrated with photoconductive switches

An in‐plane gate field‐effect transistor is characterized by ultrafast electro‐optic sampling. The transistor is monolithically integrated with photoconductive switches in coplanar waveguide and <0.5 ps measurement time resolution is achieved. The gate‐drain capacitance of the transistor is obtained as 1.8 fF at zero drain voltage from displacement current transients. The gate‐drain capacitance is dominated by parasitic capacitance and the intrinsic gate‐drain capacitance is estimated as less than 0.2 fF.

Mode-discriminating electrooptic sampling for separating guided and unguided modes on coplanar waveguide

Mode-discriminating electrooptic sampling (MEOS) of coplanar waveguides was shown to discriminate between the symmetric quasi-TEM guided mode and asymmetric field distributions including unguided electromagnetic radiation. Radiation generated in a photoconductive switch and reflected from the back of the substrate was unambiguously identified. Ultrafast sampling of devices showed features in the transmitted pulse due to multiple substrate reflections. These features are removed using MEOS, leading to increased accuracy in determination of S-parameters.

Electron heating effects in free-standing single-crystal GaAs fine wires

The authors report on experiments, and their analysis, on electron heating effects in 3.2 mu m long free-standing fine wires (triangular cross-section with approximately=0.5 mu m side) of single-crystal GaAs doped at 1017 cm-3. The data can be used to extract a thermal conductivity that has a linear temperature dependence, consistent with a contribution from electrons and/or one-dimensional phonons they show that the electronic contribution dominates.