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We develop an efficient back gate for silicon-on-insulator (SOI) devices operating at cryogenic temperatures and measure the quadratic hyperfine Stark shift parameter of arsenic donors in isotopically purified 28Si-SOI layers using such structures. The back gate is implemented using MeV ion implantation through the SOI layer forming a metallic electrode in the handle wafer, enabling large and uniform electric fields up to 2V/μm to be applied across the SOI layer. Utilizing this structure, we measure the Stark shift parameters of arsenic donors embedded in the 28Si-SOI layer and find a contact hyperfine Stark parameter of ηa = 1.9±0.7×10-3 μm²/V². We also demonstrate electric-field driven dopant ionization in the SOI device layer, measured by electron spin resonance. [ABSTRACT FROM AUTHOR]

We report measurements of spin-dependent scattering of conduction electrons by neutral donors in accumulation-mode field-effect transistors formed in isotopically enriched silicon. Spin-dependent scattering was detected using electrically detected magnetic resonance where spectra show resonant changes in the source-drain voltage for conduction electrons and electrons bound to donors. We discuss the utilization of spin-dependent scattering for the readout of donor spin states in silicon based quantum computers. [ABSTRACT FROM AUTHOR]

Strain aligned InAs quantum dots were grown on the cleaved edges of first growth samples containing strained InxGa(1-x)As layers of varying thickness and indium fraction. The formation of the cleaved-edge quantum dots was observed by means of atomic force microscopy. 100% linear alignment of InAs quantum dots over the InGaAs strain layers of the first growth sample is demonstrated. Linear density of the aligned dots was found to depend on the properties of the underlying InGaAs strain layers. Vertical alignment of an additional InAs quantum dot layer over the buried, linearly aligned, initial dot layer was observed for thin GaAs spacer layers. [ABSTRACT FROM AUTHOR]

We report advances in nanoimprint lithography, its application in nanogap metal contacts, and related fabrication yield. We have demonstrated 5 nm linewidth and 14 nm linepitch in resist using nanoimprint lithography at room temperature with a pressure less than 15 psi. We fabricated gold contacts (for the application of single macromolecule devices) with 5 nm separation by nanoimprint in resist and lift-off of metal. Finally, the uniformity and manufacturability of nanoimprint over a 4 in. wafer were demonstrated. [ABSTRACT FROM AUTHOR]

Discusses the use of ballistic electrons to study quantum structures. Three terminal ballistic transistor structure; Differential transfer ratio as function of the emitter-base voltage and devices at different temperatures; Difference between the emitter-base voltage and the electron energy due to voltage drops across the contacts and conducting layers of the structure.

We have measured the enhancement in the response of a quantum well infrared detector by the incorporation of a metallic diffraction grating into the structure. We find an enhancement ratio of about 30, and its spectrum indicates that waveguiding of diffracted light occurs within the sample. Strong coupling to evanescent modes of the grating is not observed. [ABSTRACT FROM AUTHOR]

We have studied photoluminescence from GaAs/Al0.3Ga0.7 As modulation-doped single heterojunctions, using excitation sources from infrared to ultraviolet near-liquid-helium temperature. The spectra have a strong interface component, accompanied by bulk GaAs and AlGaAs band-gap luminescence. Using ultraviolet instead of infrared as the excitation, the interface signal is greatly enhanced relative to the bulk GaAs luminescence. The interface signal can be shifted to the higher energies when a semitransparent front gate is positively biased. Our observations indicate that the interface luminescence comes from the recombination of the two-dimensional electrons with holes trapped at or near the interface. The peaks and the shoulders in the interface spectra appear to correspond to subbands of the two-dimensional electron gas at the interface. Our results demonstrate the feasibility of doing spectroscopic studies on high-mobility electrons at single heterojunctions. [ABSTRACT FROM AUTHOR]

A photovoltaic infrared detector based on photoemission from a single modulation doped GaAs-AlGaAs quantum well is presented. The modulation doping provides a built-in field which allows unbiased operation. We show results from a device which is sensitive to 180 meV (7 μm wavelength) light, with a bandwidth of 20 meV, for which we estimate the quantum efficiency to be 1%. We demonstrate that the detector may be tuned to different wavelengths by varying the width of the well. [ABSTRACT FROM AUTHOR]

We have investigated the states produced at the Si-SiO2 interface by Fowler–Nordheim tunneling and by UV photoinjection at low temperature (90 K). After the interface states are generated, subsequent application of a negative gate bias (5–6 MV/cm) converts them entirely into trapped negative charge. The reverse conversion into interface states occurs if a positive gate bias (5–6 MV/cm) is applied. Cycling of the defects between interface states and trapped negative charge is observed in both experiments. The data strongly suggest that both low-temperature Fowler–Nordheim tunneling and UV photoinjection generate essentially the same structural defect at the interface between Si and SiO2. [ABSTRACT FROM AUTHOR]

A new technique has been developed to obtain the depth profile of trapped positive charge which has been introduced into the SiO2 layer in metal-oxide-silicon structures at low temperature. We use photon-assisted tunneling at a fixed photon energy to inject electrons from the Si into the SiO2. Trapped positive charge located closer to the interface than the point at which the electrons emerge into the oxide conduction band is not affected, while that farther away can capture electrons. From the shifts of the capacitance versus voltage curves at various biases we can profile the location of the trapped positive charge. We demonstrate the use of this technique with a comparison of the positive charge introduced by x irradiation and Fowler–Nordheim tunneling (high-field stress). For the x-ray irradiated samples, the positive charge is located considerably farther (20–35 Å) from the Si-SiO2 interface than for high-field stressed samples (<20 Å). [ABSTRACT FROM AUTHOR]

An infrared detector based on the excitation of carriers out of a modulation-doped quantum well is theoretically investigated. The efficiency of the detector is increased by using a grating to enhance the fields in the well. Scattering effects are taken into account by designing the quantum well so that upon excitation carriers will escape in a short time compared to the time it takes to scatter back into the well. Despite this constraint, a quantum efficiency of 90% is shown to be possible for a GaAs-A1GaAs quantum well with a career density of 10[sup 12] cm[sup -2]. [ABSTRACT FROM AUTHOR]

We propose a new model to explain the high initial oxidation rates observed during thermal oxidation of Si in dry O[sub 2]. We show how the accumulation of fixed positive charge that develops in the SiO[sub 2] during thermal oxidation acts to reduce the concentration of holes at the Si-SiO[sub 2] interface and thereby reduces the density of broken Si-Si bonds there. It is believed that the density of broken Si bonds is a controlling factor in the oxide growth rate during the early phase of the oxidation process, when the rate is limited by the interfacial reaction mechanism. We also present experimental evidence that is consistent with the model, and is in good agreement with independent observations of the fixed oxide charge. [ABSTRACT FROM AUTHOR]

Measurements on a single quantum well infrared detector with its peak responsivity at 5.3 μm show a large Stark shift under bias. The detector has one graded barrier to enhance the effect of an electric field on the subband spacing. Several times greater change in the intersubband transition energy with applied field is obtained this way compared to the square well. Calculations show an even larger Stark shift possible with a stepped well structure. [ABSTRACT FROM AUTHOR]

We show that trapped holes at the Si-SiO2 interface account for all of the interface states generated by gate-positive irradiation of metal-oxide-silicon structures. The field-induced conversion of trapped holes to interface states is found to be the rate-limiting step in interface state buildup. Interface-state generation by hole trapping at the Si-SiO2 interface also plays a role for gate-negative irradiation. However, our experiments demonstrate an additional avenue for interface-state formation under these conditions. Holes created in the SiO2 layer are swept to the Al-SiO2 interface where they release positive ions. The transport of these ions to the Si-SiO2 interface under gate-positive field results in new interface states. Our data do not support models involving liberation of protons in the bulk of the SiO2 layer by hole transport through the oxide. [ABSTRACT FROM AUTHOR]

Electron injection into ultrathin nitrided oxides on silicon reveals both high densities of electronic defects, which readily capture electrons, and efficient tunnel emission of trapped charge. High-temperature nitridation of thermally grown oxides was verified with Auger depth profiling. In 11-17-nm-thick nitrided oxides, the electron trap density is ≥1×1019 cm-3 as determined from saturated charge accumulation, the majority of the traps are energetically situated more than 2 eV below the conduction band as determined by post-injection anneals up to 300 °C, and the capture cross section is of the order of 10-14 cm2 as estimated from the trapping kinetics. Complete extraction of trapped charge is achieved in the thinnest films (e.g., ≤11 nm thick), and the tunnel emission mechanism is evidenced by the independence of the discharge time on temperature. Implications of the above findings for applications of ultrathin nitrided oxides in very large scale integration and for their low sensitivity to ionizing radiation are discussed. [ABSTRACT FROM AUTHOR]