Professor Kevin Homewood

Reaction order in Bi-doped oxide glasses depends on the optical basicity of the glass host. Red and NIR photoluminescence (PL) bands result from Bi2+ and Bin clusters, respectively. Very similar centers are present in Bi-and Pb-doped oxide and chalcogenide glasses. Bi-implanted and Bi melt-doped chalcogenide glasses display new PL bands, indicating that new Bi centers are formed. Bi-related PL bands have been observed in glasses with very similar compositions to those in which carrier-type reversal has been observed, indicating that these phenomena are related to the same Bi centers, which we suggest are interstitial Bi2+ and Bi clusters. © 2013 Optical Society of America.

Amorphous iron disilicide (a-FeSi ) shows potential as a photovoltaic material due to its bandgap of <0.9 eV and high absorption coefficient. We present a detailed characterization of a-FeSi , with particular emphasis on the electrical properties of a-FeSi /c-Si heterostructures, under both dark and illuminated conditions. The samples were prepared on quartz and silicon substrates using RF co-sputtering of an iron/silicon target. Optical transmission spectroscopy was used to confirm the bandgap of the samples. Van der Pauw measurements and currentvoltage analysis techniques were used to determine the carrier type and conduction mechanisms of the samples. The results show that a-FeSi forms a rectifying pn heterojunction on p-type crystalline silicon. The silicide is characterized by very high carrier concentrations, resulting in the depletion region being almost entirely formed within the silicon substrate. Initial JV results suggest carrier recombination within the silicide to be the dominant contribution to the conduction across the junction, with photovoltaic effects having been observed under AM1.5 conditions. © 2012 IOP Publishing Ltd.

Carrier-type reversal to enable the formation of semiconductor p-n junctions is a prerequisite for many electronic applications. Chalcogenide glasses are p-type semiconductors and their applications have been limited by the extraordinary difficulty in obtaining n-type conductivity. The ability to form chalcogenide glass p-n junctions could improve the performance of phase-change memory and thermoelectric devices and allow the direct electronic control of nonlinear optical devices. Previously, carrier-type reversal has been restricted to the GeCh (Ch=S, Se, Te) family of glasses, with very high Bi or Pb 'doping' concentrations (~5-11 at.%), incorporated during high-temperature glass melting. Here we report the first n-type doping of chalcogenide glasses by ion implantation of Bi into GeTe and GaLaSO amorphous films, demonstrating rectification and photocurrent in a Bi-implanted GaLaSO device. The electrical doping effect of Bi is observed at a 100 times lower concentration than for Bi melt-doped GeCh glasses.

Amorphous iron disilicide (a-FeSi 2) shows potential as a photovoltaic material due to its bandgap of <0.9 eV and high absorption coefficient. We present a detailed characterization of a-FeSi 2, with particular emphasis on the electrical properties of a-FeSi 2/c-Si heterostructures, under both dark and illuminated conditions. The samples were prepared on quartz and silicon substrates using RF co-sputtering of an iron/silicon target. Optical transmission spectroscopy was used to confirm the bandgap of the samples. Van der Pauw measurements and currentvoltage analysis techniques were used to determine the carrier type and conduction mechanisms of the samples. The results show that a-FeSi 2forms a rectifying pn heterojunction on p-type crystalline silicon. The silicide is characterized by very high carrier concentrations, resulting in the depletion region being almost entirely formed within the silicon substrate. Initial JV results suggest carrier recombination within the silicide to be the dominant contribution to the conduction across the junction, with photovoltaic effects having been observed under AM1.5 conditions. © 2012 IOP Publishing Ltd.

We report amorphous GaLaSO-based resistive switching devices, with and without Pb-implantation before deposition of an Al active electrode, which switch due to deposition and dissolution of Al metal filaments. The devices set at 2-3 and 3-4 V with resistance ratios of 6 × 104 and 3 × 109 for the unimplanted and Pb-implanted devices, respectively. The devices reset under positive Al electrode bias, and Al diffused 40 nm further into GaLaSO in the unimplanted device. We attribute the positive reset and higher set bias, compared to devices using Ag or Cu active electrodes, to the greater propensity of Al to oxidise. © 2014 AIP Publishing LLC.

We investigate a new approach for efficient generation of the lasing G-centre (carbon substitutional-silicon self-interstitial complex) which crucially is fully compatible with standard silicon ultra-large-scale integration technology. Silicon wafers were implanted with carbon and irradiated with high energy protons to produce self-interstitials that are crucial in the formation of the G-centre. Rutherford backscattering spectrometry (RBS) and transmission electron microscopy were used to study the structure of the post-implanted silicon samples and to investigate the behaviour of the self-interstitials and damage introduced by the carbon and proton implantation. The effect of substrate pre-amorphisation on the G-centre luminescence intensity and formation properties was also investigated by implanting Ge prior to the carbon and proton irradiation. Photoluminescence measurements and RBS results show a significantly higher G-centre peak intensity and silicon yield, respectively, in samples without pre-amorphisation. © 2012 American Institute of Physics.

We report silicon LEDs showing light emission from 1.1 to 1.6 ¼m and demonstrate optical gain by incorporating optically active impurities. Nano-engineering enables room temperature operation. As one exemplar, we show that erbium, with local strain engineering provides useful optical emission and gain at 1.5 ¼m.

Ion implantation and thermal annealing effects on composition and structure of Ni/Ti multilayer have been studied and reported in this paper. The thin films composed of five (Ni/Ti) bilayers were deposited by d.c. ion sputtering on (100) Si wafers to a total thickness of <180 nm. Ion irradiations were performed by 180 keV Ar ions with fluence of 6 × 10 16 ions cm -2. After deposition and implantation, the samples were annealed at 400 °C for 30 min in an inert ambient. Composition and structural characterizations were performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Annealing of as-deposited samples at 400 °C induces a progressed interaction between Ni and Ti layers with the initial formation of NiTi alloy phase. Progressed alloying was achieved for the ion fluence of 6 × 10 16 ions cm -2 and the formed structure is composed of NiTi compound, only at depth around the projected ion range. In the deeper layers, beyond the projected range of implanted ions, the diffusion of Ni atoms can lead to solid state amorphization. Subsequent annealing at 400 °C for 30 min enabled enhanced interaction between intermixed Ni and Ti layers, and in the layers close to the Si substrate the conditions for the formation of intermetallic compound are created. © 2012 Elsevier Ltd. All rights reserved.

Doping of amorphous chalcogenide films of rather dissimilar bonding type and resistivity, namely, Ga-La-S, GeTe, and Ge-Sb-Te by means of ion implantation of bismuth is considered. To characterize defects induced by ionbeam implantation space-charge-limited conduction and capacitance-voltage characteristics of amorphous chalcogenide/silicon heterojunctions are investigated. It is shown that ion implantation introduces substantial defect densities in the films and their interfaces with silicon. This comes along with a gradual decrease in the resistivity and the thermopower coefficient. It is shown that conductivity in GeTe and Ge-Sb-Te films is consistent with the two-type carrier conduction model. It is anticipated that ion implantation renders electrons to become less localized than holes leading to electron conductivity in certain cases as, for example, in GeTe.

W.T. Young, S.R.P. Silva, J.V. Anguita, J.M. Shannon, K.P. Homewood, B.J. Sealy

We review progress in silicon LEDs using dislocation engineering to achieve high temperature operation, a process that is fully CMOS (Complementary Metal Oxide Semiconductor) compatible. We concentrate on devices operating in the near infra-red where high value applications are. The need for silicon emitters, lasers and optical amplifiers is discussed followed by an outline of previous approaches and possible future routes explored. Results on gain in silicon are reported and routes to electrically pumped injection lasers and optical amplifiers considered. Extension of 1.1 and 1.5 ¼m devices to other wavelengths is discussed

This study presents an optimization and characterization of amorphous Iron Disilicide (a?FeSi2) synthesized using Ion Beam Mixing (IBM) of Fe?Si multilayer structures. The layers were deposited using RF magnetron sputtering, and subsequently irradiated with Ar+ and Fe+ beams of 150 and 200 keV. Rutherford Back Scattering (RBS) analysis was used to determine the structure and level of silicidation of the samples. The nature of the band?gap and the optical absorption coefficients were determined by optical transmission analysis. The results demonstrate that the synthesis of a?FeSi2 can be achieved using this technique, with the total level of silicidation being highly dependant upon the initial structure configuration and beam parameters. Direct band?gap energies of <0.90 eV have been observed for those samples with the highest levels of silicidation, with optical absorption coefficients of < 104 cm?1. Therefore this method of fabrication has been shown to produce a?FeSi2 layers without the need for post?synthesis treatment, using established technologies without compromising the optical properties that make this material such a promising semiconductor for the photovoltaics market.

Semiconducting high manganese silicides (HMS) have attracted great research interest in the past decades for potential applications as novel optoelectronic and photovoltaic devices integrated on Si chips. The fundamental electronic properties in HMS are still unclear, and the band-gap energy was reported to scatter from 0.42 eV to 0.98 eV in the past decades. In this work, single phase semiconducting Mn4Si7 precipitates and thin films have been synthesized by ion implantation. Optical absorption spectra obtained by transmission measurements demonstrated the existence of a direct band gap in all samples. The band gap values varied in the range of 0.77 eV to 0.93 eV, corresponding to varied strain states due to different microstructures. The electronic band structures of Mn4Si7 under different strain states have been theoretically investigated by means of a full-potential linear augmented plane wave method and compared with the experimental results. From ab initio calculations, the Mn4Si7 compound is found to be a pseudo-direct band-gap semiconductor with a fundamental gap increasing linearly with the compression along c- or a-axis. This trend is in good agreement with the experimental results.

Photoluminescence at 1.2 to1.4 ¼m is demonstrated in dislocation engineered silicon substrates doped with Tm3+ leading to the development of forward biased light emitting devices operating at a turn-on voltage of only 1 V.

© 2014 Optical Society of America.We report the lattice site and symmetry of optically active Dy3+ and Tm3+ implanted Si. Local symmetry was determined by fitting crystal field parameters (CFPs), corresponding to various common symmetries, to the ground state splitting determined by photoluminescence measurements. These CFP values were then used to calculate the splitting of every J manifold. We find that both Dy and Tm ions are in a Si substitution site with local tetragonal symmetry. Knowledge of rare-earth ion symmetry is important in maximising the number of optically active centres and for quantum technology applications where local symmetry can be used to control decoherence.

We report on photoluminescence in the 1.3 and 1.7 ¼m spectral ranges in silicon doped with dysprosium. This is attributed to the Dy3+ internal transitions between the second Dy3+ excited state and the ground state, and between the third Dy3+ excited state and the ground state. Luminescence is achieved by Dy implantation into Si substrates codoped with boron, to form dislocation loops, and show a strong dependence on fabrication process. The spectra consist of several sharp lines with the strongest emission at 1736 nm, observed up to 200 K. No Dy3+ luminescence is observed in samples without B codoping, showing the paramount importance of dislocation loops to enable the Dy emission. © 2013 Optical Society of America.

© 2015 Elsevier B.V. The effects of helium ion irradiation on immiscible AlN/TiN multilayered system were studied. The structure consisted of 30 alternate AlN (~8nm) and TiN (~9.3nm) layers of a total thickness around 260nm, deposited on (100) Si substrates by reactive sputtering. The system was then implanted with 30keV He⁺ to very high irradiation doses, 1-4×10¹⁷ ions/cm². Evaluated projected ion range was 153.1±45.4nm and maximum displacements per atom for the applied doses from 6 to 24. It was found that the multilayers remained well separated and stable after irradiation to 1×10¹⁷ ions/cm², which introduces up to 10at.% of He within the structure. The main effects were agglomeration of He bubbles around the projected ion range, mostly concentrated at the AlN edges of the interfaces, and a slight increase of the mean grain size within the affected zone. Increasing of the ion dose induced further agglomeration of bubbles, splitting of the layers at the interfaces, and final destruction of the structure. The evaluated He content was consistent with the implanted dose up to 2×10¹⁷ ions/cm². For the highest dose the implanted gas is partially released from the structure. The results can be interesting towards the development of radiation tolerant materials.

The effects of Ar ion irradiation on interfacial reactions induced in Ni/Ti multilayers were investigated. Structures consisting of 10 alternate Ni (<26 nm) and Ti (<20 nm) layers of a total thickness <230 nm were deposited by ion sputtering on Si (1 0 0) wafers. Argon irradiations were done at 180 keV, to the doses of 1-6 × 1016 ions/cm2, the samples being held at room temperature. The projected implanted ion range is 86 ± 36 nm, maximum energy loss is closer to the surface, and maximum displacements per atom (dpa) from 47 to 284 for Ni and 26 to 156 for Ti. Characterizations of samples were performed by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). It is shown that ion irradiation induced a progressed intermixing in the mostly affected zone already for the lowest dose, the thickness of the mix increasing linearly with the irradiation dose. The mixed phase is fully amorphous, starting with a higher concentration of Ni (which is the diffusing species) from the initial stages, and saturating at Ni:Ti<66:34. A thick amorphous layer (<127 nm) formed towards the surface region of the structure for the irradiation dose of 4 × 1016 ions/cm2 remains stable with increasing the dose to 6 × 1016 ions/cm2, which introduces up to 6-7 at.% of Ar within the mix. The results are discussed in light of the existing models. They can be interesting for introducing a selective and controlled solid-state reaction and towards further studies of ion irradiation stability of amorphous Ni-Ti phase. © 2013 Elsevier B.V.

The effects of Ar ion irradiation on interfacial reactions induced in Ni/Ti multilayers were investigated. Structures consisting of 10 alternate Ni (<26 nm) and Ti (<20 nm) layers of a total thickness <230 nm were deposited by ion sputtering on Si (1 0 0) wafers. Argon irradiations were done at 180 keV, to the doses of 1-6 × 10 ions/cm, the samples being held at room temperature. The projected implanted ion range is 86 ± 36 nm, maximum energy loss is closer to the surface, and maximum displacements per atom (dpa) from 47 to 284 for Ni and 26 to 156 for Ti. Characterizations of samples were performed by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). It is shown that ion irradiation induced a progressed intermixing in the mostly affected zone already for the lowest dose, the thickness of the mix increasing linearly with the irradiation dose. The mixed phase is fully amorphous, starting with a higher concentration of Ni (which is the diffusing species) from the initial stages, and saturating at Ni:Ti<66:34. A thick amorphous layer (<127 nm) formed towards the surface region of the structure for the irradiation dose of 4 × 10 ions/cm remains stable with increasing the dose to 6 × 10 ions/cm, which introduces up to 6-7 at.% of Ar within the mix. The results are discussed in light of the existing models. They can be interesting for introducing a selective and controlled solid-state reaction and towards further studies of ion irradiation stability of amorphous Ni-Ti phase. © 2013 Elsevier B.V. All rights reserved.

Asymmetric contacts or split gate geometries can be used to obtain rectification, electroluminescence (EL) and photocurrent from carbon nanotube field effect transistors. Here, we report devices with both split gates and asymmetric contacts and show that device parameters can be optimised with an appropriate split gate bias, giving the ability to select the rectification direction, modify the reverse bias saturation current and the ideality factor. When operated as a photodiode, the short circuit current and open circuit voltage can be modified by the split gate bias, and the estimated power conversion efficiency was 1×10-6. When using split gates and symmetric contacts, strong EL peaking at 0.86 eV was observed with a full width at half maximum varying between 64 and 120 meV, depending on the bias configuration. The power and quantum efficiency of the EL was estimated to be around 1×10-6 and 1×10-5 respectively.

We report waveguides in Ni-doped Li2O-Ga2O 3-SiO2 (Ni:LGS) glass and glass-ceramic (GC) fabricated with a femtosecond (fs) laser with repetition rate of 1 kHz. When the glass is annealed to form a GC, the waveguides are erased. However, in the GC the waveguides are not erased by annealing. In Ni:LGS GC a 415 nm absorption band was created by fs laser waveguide writing due to the creation of Ni nanoparticles with an estimated diameter of a few nm. Raman and photoluminescence spectra of the bulk and waveguide structures were indistinguishable; however, fluorescence decay profiles indicated more long lifetime components in the waveguide compared to the bulk. © 2014 Elsevier B.V. All rights reserved.

A single carbon nanotube diode is reported, with Ti and Pd contacts, and split gates. Without gate bias the device displays strong rectification, with a leakage current (I0) of 6 × 10-16 A, and an ideality factor (·) of 1.38. When the gate above the Ti contact is biased negatively the diode inverts. When positive bias is then applied to the gate above the Pd contact minority carrier injection is suppressed. Configured such I0 and · were 2 × 10-14 A and 2.01, respectively. Electrical characterization indicates that the Schottky barrier height for electrons is lower for the Pd contact than the Ti contact. © 2013 AIP Publishing LLC.

We report on photoluminescence in the 1.7-2.1 ¼m range of silicon doped with thulium. This is achieved by the implantation of Tm into silicon that has been codoped with boron to reduce the thermal quenching. At least six strong lines can be distinguished at 80 K; at 300 K, the spectrum is dominated by the main emission at 2 ¼m. These emissions are attributed to the trivalent Tm(3+) internal transitions between the first excited state and the ground state.

Photoluminescence (PL) and excitation spectra of Bi melt-doped oxide and chalcogenide glasses are very similar, indicating the same Bi center is present. When implanted with Bi, chalcogenide, phosphate and silica glasses, and BaF2 crystals, all display characteristically different PL spectra to when Bi is incorporated by melt-doping. This indicates that ion implantation is able to generate Bi centers which are not present in samples whose dopants are introduced during melting. Bi-related PL bands have been observed in glasses with very similar compositions to those in which carrier-type reversal has been observed, indicating that these phenomena are related to the same Bi centers, which we suggest are interstitial Bi2+ and Bi clusters.

We, the organizing committee of APAC-SILICIDE 2010 Tsukuba, are very pleased to publish the fourth special issue of Thin Solid Films for scientists, researchers and students who have interests in the science and technology of semiconducting silicides and related materials.

We have measured the near-infrared photoluminescence spectrum of phosphorus doped silicon (Si: P) and extracted the donor-bound exciton (D0X) energy at magnetic fields up to 28 T. At high field the Zeeman effect is strongly nonlinear because of the diamagnetic shift, also known as the quadratic Zeeman effect (QZE). The magnitude of the QZE is determined by the spatial extent of the wave-function. High field data allows us to extract values for the radius of the neutral donor (D0) ground state, and the light and heavy hole D0X states, all with more than an order of magnitude better precision than previous work. Good agreement was found between the experimental state radius and an effective mass model for D0. The D0X results are much more surprising, and the radius of the mJ=±3/2 heavy hole is found to be larger than that of the mJ=±1/2 light hole.

This study reports on high energy bismuth ion implantation into silicon with a particular emphasis on the effect that annealing conditions have on the observed hyperfine structure of the Si:Bi donor state. A suppression of donor bound exciton, D0X, photoluminescence is observed in implanted samples which have been annealed at 700 °C relating to the presence of a dense layer of lattice defects that is formed during the implantation process. Hall measurments at 10 K show that this implant damage manifests itself at low temperatures as an abundance of p?type charge carriers, the density of which is observed to have a strong dependence on annealing temperature. Using resonant D0X photoconductivity, we are able to identify the presence of a hyperfine structure in samples annealed at a minimum temperature of 800 °C; however, higher temperatures are required to eliminate effects of implantation strain.

Silicon photonics has gained more popularity in the last decade stimulated by a series of recent breakthroughs and attractive potential applications in the integrated-optics. One of the great challenges is to modify the silicon lattice so as to enhance the light emission properties. Moreover, by referring to Moore?s Law, there are concerns of the increase in interconnect time delay which can surpass the switching time if the gate length in transistors are continued to scale down. By implementing the silicon optical emitter on the integrated circuit, it will eliminate this major problem thus enhancing the performance and speed of the computer. This work will focus on researching the point defect especially the G-centre in silicon as a potential technique to emit coherent light from silicon. We have investigated and presented a new approach to incorporate high levels of the emissive G-centre peaking sharply at 1280 nm by implanting carbon and protons into the silicon lattice. Significantly this technique utilizes fully ULSI technology compatible processes such as ion implantation and high temperature annealing. Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM) techniques were used along with the photoluminescence measurement to correlate the optical and structural properties of the G-centre formed by the carbon implantation and high energy ion irradiation. The analysis reveals that the silicon interstitials generated after proton irradiation are an essential factor in forming the G-centre complex. We have also introduced the dislocation engineering technique into the silicon lattice with the G-centre complexes. The results are promising and with optimization of the technique to introduce the dislocation loops into the G-centre technique, the temperature quenching problem often related to the optically active point-defect centre, may be solved. Electroluminescence (EL) measurements were carried out after the fabrication of the LED devices. Results from the sample with the G-centre luminescence is the most crucial as it shows that by using the proposed technique in this research, luminescence from silicon is indeed possible when electrically pumped. This is an essential key result for the future research of the optically active point-defect especially the G-centre towards the possibility of an electrically pumped, efficient silicon laser.

One of the greatest challenges in silicon photonics has been to induce light emission in silicon, with the ultimate vision is to have fully silicon-based photonics emitters or lasers which can operate by both optical and electrical pumping. Comprehensive photoluminescence (PL) and electroluminescence (EL) studies are conducted on dislocation engineering light emitting diode structures based on silicon implanted (Si:B) with Ce, Eu, and Yb rare-earth (RE) ions. The PL and EL results show very bright luminescence intensity and dramatic red shifting in luminescence peaks which shows a possible novel phenomenon of RE energy transition modification. The modification is attributed to the direct transition from Si conduction band edge to RE manifolds? (_^2)F?_(7/2)^ , ?(_^2)F?_(5/2)^ for ?Ce?^(3+), ?(_^7)F?_j^ (j=0 to 4) for ?Eu?^(3+), ?(_^2)F?_(5/2)^ and ?(_^2)F?_(7/2)^ for ?Yb?^(3+). The emissions are shifted from the conventional lowest internal energy transition in ?Ce?^(3+) from around blue spectrum at ~350 nm (due to (_^2)D_(3/2)^ excited state to the ?(_^2)F?_(7/2)^ , ?(_^2)F?_(5/2)^ transitions) to ~1.35 µm in Si:B&Ce. For ?Eu?^(3+) the emission is shifted from around the red spectrum at ~600 nm (due to (_^5)D_0^ excited state to the ?(_^7)F?_j^ transitions, j=0 to 4) to ~ 1.40 µm in Si:B&Eu and for ?Yb?^(3+) is shifted from slightly beyond the visible region at ~980 nm (due to ?(_^2)F?_(5/2)^ excited state to the ?(_^2)F?_(7/2)^ transition) to ~ 1.43 µm in Si:B&Yb samples. The new shifting of luminescence peak into NIR region is very important for optical communication in making LEDs and lasers.

This study reports the effect of an increasing ion dose on both the electrical activation yield and the characteristic properties of implanted bismuth donors in silicon. A strong dependence of implant fluence is observed on both the yield of bismuth donors and the measured impurity diffusion. This is such that higher ion concentrations result in both a decrease in activation and an enhancement in donor migration through interactions with mobile silicon lattice vacancies and interstitials. Furthermore, the effect of implant fluence on the properties of the Si:Bi donor bound exciton, D⁰X, is also explored using photoluminescence (PL) measurements. In the highest density sample, centers corresponding to the PL of bismuth D⁰Xs within both the high density region and the lower concentration diffused tail of the implanted donor profile are identifiable.

By measuring the centroid of a beam on a detector, one can track the movement of that beam across the detector. By tracking this movement, one can track the object encompassing the detector, for example, a spacecraft. A variety of system-specific performance inhibitors can make this a challenge, requiring a robust calibration method. The goal of this investigation is to model the true beam position of the instrument in terms of the measured beam position. For this, a mathematical model is created that interpolates and corrects the measured beam position using precollected position data?a "calibration model." The real-world scenario for this investigation is the flight-representative model of the fine lateral and longitudinal sensor (FLLS) instrument, built by Neptec Design Group and Neptec UK for the European Space Agency mission PROBA-3. Performance inhibitors for FLLS are cropping of the beam, imperfect optics, and a varying distance the beam has traveled (up to 250 m). Using bivariate spline interpolation for the FLLS calibration model gives the best performance, achieving a measurement accuracy well within the mission requirement of <300 ¼m.