We have investigated the use of conventional ion implantation to fabricate enriched 28Si layers for use in quantum computers. The final compositions of samples enriched using ultra-low energy (ULE) (800 eV and 2 keV) and low energy (20 keV) 28Si implants of varying fluences (1 × 1016–3.8 × 1017 cm−2) using two different implanters were measured using channelled Rutherford Backscattering Spectroscopy (RBS). The dynamic, binary collision approximation program TRIDYN was used to model the implantation profiles to guide the analysis of the RBS spectra. It was found that ULE implants achieved high 28Si enrichment levels but were heavily contaminated with oxygen due to poor vacuum in the implanter wafer end station. It was shown that oxidation could be reduced by using an accelerator with an end station with better vacuum and increasing the implant energy to 20 keV. However, TRIDYN simulations predict that the best 28Si enrichment levels that could be achieved under these conditions would saturate at ∼99.2% due to self-sputtering. We modelled a range of conditions with TRIDYN and so recommend low energies (<3 keV), ultra-high vacuum implantation for high 28Si enrichment (>99.9%) with the lowest possible fluences (∼5–10 × 1017 cm−2).

The effect of the temperature ranging from cryogenics to room temperature were investigated on the formation of the optically-active point defect called the G-centre. The G-centre as an emissive point defect gained a lot of attention recently due to its sharp zero phonon luminescence peak at a wavelength of 1.28 mu m (0.97 eV) with the evidence of lasing occurred in the structure. The emission of the G-centre is attributed to the carbon substitutional-carbon interstitial (CsCi) complex which interacts with silicon interstitials during the damage event. This complex is generated by implantation of carbon and followed by proton irradiation. Prior to the carbon implantation, two of the samples were pre-amorphised by germanium. Photoluminescence (PL) measurements were carried out at temperature ranging from 80 K up to room temperature to observe the intensity of the main peaks. The results confirm that the main peaks of point-defect centre in all of the samples including the G-centre suffer from the temperature quenching. However, the peak intensity for some of the wavelength especially the ones with high FWHM, do perform better at high temperature. The temperature quenching phenomena observed in the point-defect technique is the main problem that needs to be addressed and solved before realizing the method in the all silicon photonic system.

Obtaining high level active n+ carrier concentrations in germanium (Ge) has been a significant challenge for further development of Ge devices. By ion implanting phosphorus (P) and fluorine (F) into Ge and restoring crystallinity using Nd:YAG nanosecond pulsed laser melting (PLM), we demonstrate 1020 cm−3 n+ carrier concentration in tensile-strained epitaxial germanium-on-silicon. Scanning electron microscopy shows that after laser treatment, samples implanted with P have an ablated surface, whereas P + F co-implanted samples have good crystallinity and a smooth surface topography. We characterize P and F concentration depth profiles using secondary ion mass spectrometry and spreading resistance profiling. The peak carrier concentration, 1020 cm−3 at 80 nm below the surface, coincides with the peak F concentration, illustrating the key role of F in increasing donor activation. Cross-sectional transmission electron microscopy of the co-implanted sample shows that the Ge epilayer region damaged during implantation is a single crystal after PLM. High-resolution X-ray diffraction and Raman spectroscopy measurements both indicate that the as-grown epitaxial layer strain is preserved after PLM. These results demonstrate that co-implantation and PLM can achieve the combination of n+ carrier concentration and strain in Ge epilayers necessary for next-generation, high-performance Ge-on-Si devices.

Space photovoltaics is dominated by multi‐junction (III‐V) technology. However, emerging applications will require solar arrays with high specific power (kW/kg), flexibility in stowage and deployment, and a significantly lower cost than the current III‐V technology offers. This research demonstrates direct deposition of thin film CdTe onto the radiation‐hard cover glass that is normally laminated to any solar cell deployed in space. Four CdTe samples, with 9 defined contact device areas of 0.25 cm2, were irradiated with protons of 0.5‐MeV energy and varying fluences. At the lowest fluence, 1 × 1012 cm−2, the relative efficiency of the solar cells was 95%. Increasing the proton fluence to 1 × 1013 cm−2 and then 1 × 1014 cm−2 decreased the solar cell efficiency to 82% and 4%, respectively. At the fluence of 1 × 1013 cm−2, carrier concentration was reduced by an order of magnitude. Solar Cell Capacitance Simulator (SCAPS) modelling obtained a good fit from a reduction in shallow acceptor concentration with no change in the deep trap defect concentration. The more highly irradiated devices resulted in a buried junction characteristic of the external quantum efficiency, indicating further deterioration of the acceptor doping. This is explained by compensation from interstitial H+ formed by the proton absorption. An anneal of the 1 × 1014 cm−2 fluence devices gave an efficiency increase from 4% to 73% of the pre‐irradiated levels, indicating that the compensation was reversible. CdTe with its rapid recovery through annealing demonstrates a radiation hardness to protons that is far superior to conventional multi‐junction III‐V solar cells.

Co-doping with fluorine is a potentially promising method for defect passivation to increase the donor electrical activation in highly doped n-type germanium. However, regular high dose donor-fluorine co-implants, followed by conventional thermal treatment of the germanium, typically result in a dramatic loss of the fluorine, as a result of the extremely large diffusivity at elevated temperatures, partly mediated by the solid phase epitaxial regrowth. To circumvent this problem, we propose and experimentally demonstrate two non-amorphizing co-implantation methods; one involving consecutive, low dose fluorine implants, intertwined with rapid thermal annealing and the second, involving heating of the target wafer during implantation. Our study confirms that the fluorine solubility in germanium is defect-mediated and we reveal the extent to which both of these strategies can be effective in retaining large fractions of both the implanted fluorine and, critically, phosphorus donors.

Germanium is one of the strongest candidate materials for next generation integrated optoelectronic devices owing to its high carrier mobilities, bandgap at the telecom wavelength of 1.55 mu m, and monolithic (CMOS) integration with silicon. However, for device applications requiring very high carrier concentrations, such as solid state lasers and MOSFETs, a persistent technological hurdle is the limited electrically active concentration similar to 5x10(19) cm(-3) observed in n-type material, regardless of the chemical concentration of incorporated donors above this. This is due to the formation of donor-vacancy clusters, which electrically compensate the material and enhance dopant diffusivity. In recent years, multiple strategies have attempted to address this, with some, albeit limited, success. Here we outline some of the more novel approaches and provide a review with particular emphasis on one of the more promising of these: the co-implantation of donors with fluorine, and discuss potential methods for optimizing this process.

We present an all-optical technique for measuring the quantum efficiency (QE) of luminescent materials; and, although generally applicable, we apply it as an example to silicon nanocrystals. The concept of internal quantum efficiency (IQE) for a light emission process; the fraction of electron-hole pairs that generate photons inside a material is quite a simple one, and yet in practice this is very difficult to measure. In fact, all existing methods rely on an estimation of IQE from the externalquantum efficiency (EQE); the ratio of photons emitted to those absorbed, typically with the assumption that IQE tends to unity at low temperature. This is an over-simplification and requires further assumptions about the dielectric materials that the photons traverse. An alternative approach was proposed earlier [1], in which both the light and heat, generated by the excitation process, are measured simultaneouslyas functions of a third variable, e.g. excitation laser power. However, experimental limitations such as reabsorption of light in the sample and recovery of a non-local thermal signal mean that only the EQE is ever really determined, albeit accurately [2]. In this contribution, we describe an all-optical (pump-probe) technique in which we balance the light leaving a local (μm-scale) region of excitation (by measuring μ-PL) with the heat generated at the focussed laser spot (by measuring changes in intensity of a near-IR reflected probe). Critically, our optical arrangement (three confocal signals in one microscope objective) combined with an advanced DSP ‘lock-in’ technique, permits measurement of ΔR/R to within 1 part in 106, corresponding to temperature changes on the mK scale. We present initial data on silicon nanocrystals, formed in glass cover-slips after ion implantation and thermal annealing, and discuss how the technique relates to a true measure of IQE with limitations and how it can be applied more generally to alternative material systems. References [1] D J Dunstan, ‘On the measurement of absolute radiative and non-radiative recombination efficiencies in semiconductor lasers’, J. Phys. D: Appl. Phys. 25 (1992) 1825 – 1828 [2] K R Catchpole et al, ‘High external quantum efficiency of planar semiconductor strucutres’, Semicond. Sci. Technol. 19 (2004) 1232 – 1235

We report on the super enhancement of the 1.54 μm Er emission in erbium doped silicon-on-insulator when codoped with oxygen at a ratio of 1:1. This is attributed to a more favourable crystal field splitting in the substitutional tetrahedral site favoured for the singly coordinated case. The results on these carefully matched implant profiles show that optical response is highly determined by the amount and ratio of erbium and oxygen present in the sample and ratios of O:Er greater than unity are severely detrimental to the Er emission. The most efficient luminescence is forty times higher than in silicon-on-insulator implanted with Er only. This super enhancement now offers a realistic route not only for optical communication applications but also for the implementation of silicon photonic integrated circuits for sensing, biomedical instrumentation and quantum communication.

We report a new approach of generating the dicarbon G-centre on silicon substrates by utilizing technique that is fully compatible with the standard silicon ultra-large-scale integration (ULSI) 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. Prior to that, all the samples were pre-amorphised with germanium. Photoluminescence (PL) measurements at 80 K were carried out to investigate the point defect mediated luminescence of the G-centre with a wavelength of 1280 nm. The results show a prominent, sharp luminescence at the carbon related, G centre in majority of the samples.

Silicon underpins microelectronics but lacks the photonic capability needed for next‐generation systems and currently relies on a highly undesirable hybridization of separate discrete devices using direct band gap semiconductors. Rare‐earth (RE) implantation is a promising approach to bestow photonic capability to silicon but is limited to internal RE transition wavelengths. Reported here is the first observation of direct optical transitions from the silicon band edge to internal f‐levels of implanted REs (Ce, Eu, and Yb); this overturns previously held assumptions about the alignment of RE levels to the silicon band gap. The photoluminescence lines are massively redshifted to several technologically useful wavelengths and modeling of their splitting indicates that they must originate from the REs. Eu‐implanted silicon devices display a greatly enhanced electroluminescence efficiency of 8%. Also observed is the first crystal field splitting in Ce luminescence. Mid‐IR silicon photodetectors with specific detectivities comparable to existing state‐of‐the‐art mid‐IR detectors are demonstrated.

Plasmons in the visible/UV energy regime have attracted great attention, especially in nano-materials, with regards to applications in opto-electronics and light harvesting; tailored enhancement of such plasmons is of particular interest for prospects in nano-plasmonics. This work demonstrates that it is possible, by adequate doping, to create excitations in the visible/UV regime in nano-carbon materials, i.e., carbon nanotubes and graphene, with choice of suitable ad-atoms and dopants, which are introduced directly into the lattice by low energy ion implantation or added via deposition by evaporation. Investigations as to whether these excitations are of collective nature, i.e., have plasmonic character, are carried out via DFT calculations and experiment-based extraction of the dielectric function. They give evidence of collective excitation behaviour for a number of the introduced impurity species, including K, Ag, B, N, and Pd. It is furthermore demonstrated that such excitations can be concentrated at nano-features, e.g., along nano-holes in graphene through metal atoms adhering to the edges of these holes.

Interfacing rare-earth-doped crystals with superconducting circuit architectures provides an attractive platform for quantum memory and transducer devices. Here, we present the detailed characterization of such a hybrid system: a locally implanted rare-earth Gd3+ in Al2O3 spin system coupled to a superconducting microresonator. We investigate the properties of the implanted spin system through angular-dependent microresonator electron spin resonance (micro-ESR) spectroscopy. We find, despite the high-energy near-surface implantation, the resulting micro-ESR spectra to be in excellent agreement with the modeled Hamiltonian, supporting the integration of dopant ions into their relevant lattice sites while maintaining crystalline symmetries. Furthermore, we observe clear contributions from individual microwave field components of our microresonator, emphasizing the need for controllable local implantation.

Continued effort has been placed on maximizing activation while controlling the diffusion of silicon doping in InGaAs for present and future complementary metal-oxide semiconductor devices. In order to explore the diffusion and activation behavior, Si marker layers were grown in InGaAs on InP by molecular beam epitaxy. The nature of Si diffusion was explored using a series of isoelectronic implants to introduce excess point defects near the layer. It was observed that excess interstitials reduce the Si diffusion consistent with a vacancy-driven diffusion mechanism. A diffusion and activation model implemented in the Florida object oriented process simulator has been developed to predict silicon diffusion behavior over a variety of temperatures and times. Using current and previous experimental data and complimentary density functional theory results, the diffusion model employs the SiIII–VIII pair as the primary mechanism for silicon diffusion in InGaAs.

I F Crowe, M Ishii, M P Halsall, R M Gwilliam, A P Knights and B Hamilton The University of Manchester, Manchester M13 9PL UK NIMS, Tsukuba, Ibaraki, 305-0047 Japan University of Surrey, Guildford GU2 7XH UK McMaster University, Hamilton, ON L8S 4L7 Canada e-mail: iain.crowe @manchester.ac.uk This talk will provide an overview of the optoelect ronic properties of silicon nanocrystals (Si-nc’s), formed from a supersaturated SiO x matrix prepared by Si + implantation of SiO2 and rapid thermal processing. In order to improve the light emission (or doping) eff iciency, such that these materials may find applica tion in future (opto-) electronic devices, it is critical t ha we understand the non-radiative mechanisms. As such we will examine here the effects of early s tage annealing and surface passivation via hydrogen n the Si-nc photoluminescence (PL) spectra, which ind icates that one of the key de-excitation pathways i s carrier trapping at the P b-type (dangling bond) defect. We will also look at the effects of co-doping Si-nc ’s with erbium (Er), which can provide an intense emission at the technologically important wavelengt h of 1534nm as a result of Si-nc ‘sensitized’ Er 3+ f-shell excited to ground state transitions. The role of th e Si-nc’s in enhancing this emission remains unclea r but we have examined the effect of the Si-nc size on th e Er related PL transients, which reveal a multi-exponential character indicative of the local environment of the emitting centres. Detailed anal ysis reveals two distinct classes of luminescent Er; one exhibiting a relatively short lifetime (few ms) an d the second, exhibiting a much longer lifetime (10 to 15 ms). The latter is characteristic of that of Er in stoichiometric SiO2, i.e. far from any Si-nc’s, whilst the former may be attributed to a Purcell-like enhancement of the radiative rate induced by local ch nges in the refractive index for Er ions close t o a spherical dielectric interface (i.e. the Si-nc). We pr sent the results of our recent studies on the S i-nc:Er system via electrical frequency response measuremen ts that points to a trapping centre formed by the E r itself, through which excited carriers can recombin e non-radiatively [1]. Finally, co-doping Si-nc’s with shallow donors such as phosphorus (P) is of interest for future nano-electronic devices. However, whilst it is know that the Si-nc PL is quenched with increasing P concentration, the mechanism is not fully understoo d. Our studies suggest that this is due to an effic i nt Auger assisted non-radiative recombination process where the energy of photo-excited carriers is released by electron collisions with activated P donors in S i-nc’s [2]. We present our most recent results in w hich the effects of this Auger mechanism are directly probed using an electrical frequency response analysis [3].

We report and compare the luminescence, both photo- and electroluminescence, in the near-infrared of a wide range of rare earths (Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm) doped dislocation engineered silicon light emitting devices. The rare earths are introduced using ion implantation into standard Czochralski (CZ) n-type silicon wafers pre-implanted with boron to form both the p-n junction and an engineered dislocation loop array. Rare earth internal transitions are observed in samples co-doped with Dy, Ho, Er, and Tm. We show that for each rare earth optimizing the optical activity depends critically on the rare earth implant parameters and post-implant process conditions. Room temperature operation in the 1.5 and 2.0 mu m spectral regions is observed from the internal rare earth transitions in Er and Tm. (C) 2015 The Japan Society of Applied Physics

This work presents a study of application of secondary ion mass spectrometry (SIMS) to measure tin concentration in Ge1-xSnx alloy with x higher than solid solubility similar to 1%, i.e. well above the diluted regime where SIMS measurements usually provide the most reliable quantitative results. SIMS analysis was performed on Sn+ ion implanted Ge films, epitaxially deposited on Si, and on chemical vapor deposition deposited Ge0.93Si0.07 alloy. Three SIMS conditions were investigated, varying primary beam ion species and secondary ion polarity keeping 1 keV impact energy. Best depth profile accuracy, best agreement with the fluences measured by Rutherford backscattering spectrometry, good detection limit (similar to 1 x 10(17) at/cm(3)) and depth resolution (similar to 2 nm/decade) are achieved in Cs+/SnCs+ configuration. However, applied sputtering conditions (Cs+ 1 keV, 64 degrees incidence vs. normal) induced an early formation of surface topography on the crater bottom resulting in significant variation of sputtering yield. Atomic force microscopy shows a peculiar topography developed on Ge: for oblique incidence, a topography consisting in a sequence of dots and ripples was observed on the crater bottom. This behavior is unusual for grazing incidence and has been observed to increase with the Cs+ fluence. Rotating sample during sputtering prevents this ripple formation and consequently improves the depth accuracy. (C) 2015 Elsevier B.V. All rights reserved.

The ability to control dynamics of quantum states by optical interference, and subsequent electrical read-out, is crucial for solid state quantum technologies. Ramsey interference has been successfully observed for spins in silicon and nitrogen vacancy centres in diamond, and for orbital motion in InAs quantum dots. Here we demonstrate terahertz optical excitation, manipulation and destruction via Ramsey interference of orbital wavepackets in Si:P with electrical read-out. We show milliradian control over the wavefunction phase for the two-level system formed by the 1 s and 2 p states. The results have been verified by all-optical echo detection methods, sensitive only to coherent excitations in the sample. The experiments open a route to exploitation of donors in silicon for atom trap physics, with concomitant potential for quantum computing schemes, which rely on orbital superpositions to, for example, gate the magnetic exchange interactions between impurities.

From measurements over the last two years we have demonstrated that the charge collection system based on Faraday cups can robustly give near-1% absolute implantation fluence accuracy for our electrostatically scanned 200 kV Danfysik ion implanter, using four-point-probe mapping with a demonstrated accuracy of 2%, and accurate Rutherford backscattering spectrometry (RBS) of test implants from our quality assurance programme. The RBS is traceable to the certified reference material IRMM-ERM-EG001/BAM-L001, and involves convenient calibrations both of the electronic gain of the spectrometry system (at about 0.1% accuracy) and of the RBS beam energy (at 0.06% accuracy). We demonstrate that accurate RBS is a definitive method to determine quantity of material. It is therefore useful for certifying high quality reference standards, and is also extensible to other kinds of samples such as thin self-supporting films of pure elements. The more powerful technique of Total-IBA may inherit the accuracy of RBS.