David Donnelly

Far-infrared spectroscopic, magnetotransport, and x-ray study of athermal annealing in neutron-transmutation-doped silicon

We present evidence that the energy introduced by a short laser pulse focused to high intensity on a small spot on the surface of neutron-transmutation-doped silicon electrically activates impurities far away from the focal spot. The activation of the impurities is measured by far-infrared spectroscopy of shallow donor levels and by magnetotransport characterization. Electrical activity is comparable to that obtained with conventional thermal annealing. X-ray rocking curve measurements show strain in the area of the focal spot, but none at large distances from the focal spot.

Athermal annealing of low-energy boron implants in silicon

Silicon samples that have been ion implanted with boron at energies below 3 keV have been athermally annealed. The annealing process has been characterized using secondary ion mass spectrometry and infrared absorption spectroscopy. The athermally annealed samples show activation comparable to that for thermally annealed samples, but with much less boron diffusion. The activation in the athermally annealed samples is shown to be much higher than would be achieved by recrystallization of the amorphous layer.

Athermal annealing of phosphorus-ion-implanted silicon

A 1 cm2 area in phosphorus-implanted silicon samples is annealed by irradiation of a much smaller 0.002 cm2 area with a single laser pulse. Resistivity of the annealed region is uniform and similar to that measured after thermal annealing. Electrically activated donors did not diffuse into the sample and only slightly towards the sample surface. The process is 100% reproducible. We present evidence that the annealing is not caused by heat.

Understanding the learning assistant experience with physics identity

Learning Assistants (LAs) have been shown to have better conceptual understanding and more favorable beliefs about science than non-LAs, and are more likely to choose a career in K-12 science teaching [1]. We propose that connections between elements of identity, persistence, and participation in an LA program can be explained using the concept of the community of practice and its intimate relationship to identity [2]. In separate work, Hazari et al. found that physics identity was highly correlated to expressed career plans in physics [3]. We hypothesize that a thriving LA program has many features of a well-functioning community of practice and contributes to all four elements of physics identity: personal interest, student performance, competence, and recognition by others. We explore how this analysis of the LA experience might shape decisions and influence outcomes of adoption and adaptations of the LA model.

Athermal annealing of ion-implanted silicon

Phosphorus, arsenic, and boron dopants in neutron-transmutation-doped and ion-implanted silicon were electrically activated by a technique that does not involve the direct application of heat as in conventional thermal annealing or pulsed laser annealing. Dopants activated by this method exhibit much less diffusion than donors activated by standard thermal methods.

Athermal Annealing of Silicon

We experimentally demonstrate the annealing and electrical activation of doped silicon without the direct application of heat as in conventional thermal annealing or pulsed laser annealing. 25 × 25 × 3 mm samples of silicon doped by neutron transmutation were irradiated with a short pulse from a 1.06-micron laser. The few joule laser pulse was focused to mm-diameter surface spot which resulted in high power (∼ 10 11 W/cm 2 ) capable of launching shocks into the entire sample. In a few instances the entire silicon slab, including regionsfar outside the illuminated spot, was annealed and electrically activated. In the annealed samples electrical activation of donors throughout the slab, measured with a four-point probe, was uniform and comparable to that of thermally annealed control samples. Far-infrared spectroscopy and Hall measurements also showed that the donor species was activated and Raman spectroscopy demonstrated marked improvement in the crystal structure. We conjecture that the annealing was caused by the mechanical energy that was launched into the slab by the laser pulse. Results of experiments on an ion-implanted silicon sample are also discussed.

Graded potential wells with quasi-uniform charge distribution

Abstract We report on the growth and the characterization of several quasi-three-dimensional electron systems as realized in modulation-doped graded potential wells. We study the charge distribution, the subband structure, and the electronic properties of the samples by means of capacitance-voltage techniques as well as by the investigation of the cyclotron resonance at low temperatures. The results of our investigations are fed back into the growth conditions, which leads to the production of symmetrical, quasi-uniform charge distributions with three-dimensional properties.

Infrared Spectroscopy of Epitaxial Antimony Sulpho Iodide Thin Films

Thin films of antimony sulpho iodide (SbSI) were grown on platinized silicon substrates by the pulsed laser deposition method. As grown films were amorphous and annealing at 250 °C for 5 minutes introduced crystallinity in the films. Infrared reflectance measurements were done in the frequency range ~ 500 – 5000 cm -1 (wavelength ~ 2–20 µm). The reflectance measurements were taken at temperatures above and below the ferroelectric transition of SbSI ~ 20° C. The index of refraction for a (121) oriented film was determined to be 2.83 ± 0.35 at a temperature of 25.6 °C, and 2.80 ± 0.35 at a temperature of 9.6 °C. For a (002) oriented film, the index was 3.82 ± 0.48 at a temperature of 26.5 °C, and 3.76 ± 0.48 at a temperature of 8.0 °C. Pyro-optic coefficients of 1.5 x 10 -3 °C -1 for the (121) oriented film, and 3.2 x 10 -3 °C -1 for the (002) oriented film were obtained. These results are consistent with measurements done in the visible region, and demonstrate the potential of SbSI as an infrared detector material.

Crystal growth and properties of a new member of Pb-K-niobate series

Abstract A new member in the tungsten-bronze family of ferroelectric lead-potassium-niobate (PKN), with general formula Pb1-xK2xNb2O6, has been grown as bulk single crystal. Growth of PKN with charge composition x = 0.23 has been achieved using the Czochralski technique of crystal pulling. Large diameter boules were grown in platinum crucibles at temperatures between 1280 °C and 1300°C. Crystallographic studies were conducted using X-ray diffraction techniques. The samples were characterized for ferroelectric properties between 25 °C and 600 °C and for optical absorption. This paper presents the crystal synthesis and the results of ferroelectric and optical characterization.

Properties of InAs/(Ga,In)Sb strained layer superlattices grown on the {111} orientations

Following the proposal of the extreme type-II InAs/(Ga,In)Sb strained layer superlattice system by Mailhiot and Smith in 1987 for long wavelength infrared detection, a number of groups have experimentally investigated (100) oriented InAs/(Ga,In)Sb strained layer superlattices and demonstrated that these structures can possess energy gaps in the 8–12 μm range with absorption coefficients comparable to HgCdTe. However, a number of advantages are predicted if these structures are grown on the {111} orientations. In this paper, we present details of our investigation of the growth of InAs/GaSb heterostructures and InAs/(Ga,In)Sb strained layer superlattices on the (111)A and (111)B orientations by molecular beam epitaxy, compared to growth on the (100) orientation. Heterojunction growth and incorporation rates of Sb (As) into InAs (GaSb) on (111)A, (111)B, and (100) orientations have been assessed and implications for growth and optical properties of InAs/(Ga,In)SB strained layer superlattices are discussed. GaSb/InAs and InAs/GaSb interfaces on the (111)B orientation are investigated by x-ray photoelectron spectroscopy, and the structural quality of InAs/(Ga,In)Sb strained layer superlattices are investigated by x-ray diffraction.