Publications

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Semiconductor-insulator interfaces play an important role in the reliability of integrated devices; however, the impact of these interfaces on the physical mechanisms related to single-event effects has not been previously reported. We present experimental data that demonstrate that single-event charge collection can be impacted by changes in interface quality. The experimental data, combined with simulations, show that single-event response may depend on surface recombination at interface defects. The effect depends on strike location and increases with increasing linear energy transfer (LET). Surface recombination can affect single-event charge collection for interfaces with a surface recombination velocity (SRV) of 1000 cm/s and is a dominant charge collection mechanism with SRV > 10^{5} cm/s.

In this work, we present a new Li source for focused ion beam applications. Based on an AuSi eutectic alloy, Li is added as an impurity to minimize effects from degradation when exposed to air. We show the source is stable over the course of an hour and spot sizes ≲10 nm can be achieved. The Li beam can achieve hundreds of nanometer ranges in semiconductors with minimal damage being generated along the path length. The source performance is evaluated through a high-resolution ion beam induced charge collection experiment on an Si-based detector. Further application of the source for ion beam analysis is numerically explored; the example investigated is based on probing a semiconductor heterostructure through a Rutherford backscattering experiment, where the Li beam can reveal information that is inaccessible with either low energy or high energy He projectiles used as probes.

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GaN has electronic properties that make it an excellent material for the next generation of power electronics; however, its radiation hardening still needs further understanding before it is used in radiation environments. In this work we explored the response of commercial InGaN LEDs to two different radiation environments: ion and gamma irradiations. For ion irradiations we performed two types of irradiations at the Ion Beam Lab (IBL) at Sandia National Laboratories (SNL): high energy and end of range (EOR) irradiations. For gamma irradiations we fielded devices at the gamma irradiation facility (GIF) at SNL. The response of the LEDs to radiation was investigated by IV, light output and light output vs frequency measurements. We found that dose levels up to 500 krads do not degrade the electrical properties of the devices and that devices exposed to ion irradiations exhibit a linear and non- linear dependence with fluence for two different ranges of fluence levels. We also performed current injection annealing studies to explore the annealing properties of InGaN LEDs.

A central challenge in developing quantum computers and long-range quantum networks is the distribution of entanglement across many individually controllable qubits1. Colour centres in diamond have emerged as leading solid-state ‘artificial atom’ qubits2,3 because they enable on-demand remote entanglement4, coherent control of over ten ancillae qubits with minute-long coherence times5 and memory-enhanced quantum communication6. A critical next step is to integrate large numbers of artificial atoms with photonic architectures to enable large-scale quantum information processing systems. So far, these efforts have been stymied by qubit inhomogeneities, low device yield and complex device requirements. Here we introduce a process for the high-yield heterogeneous integration of ‘quantum microchiplets’—diamond waveguide arrays containing highly coherent colour centres—on a photonic integrated circuit (PIC). We use this process to realize a 128-channel, defect-free array of germanium-vacancy and silicon-vacancy colour centres in an aluminium nitride PIC. Photoluminescence spectroscopy reveals long-term, stable and narrow average optical linewidths of 54 megahertz (146 megahertz) for germanium-vacancy (silicon-vacancy) emitters, close to the lifetime-limited linewidth of 32 megahertz (93 megahertz). We show that inhomogeneities of individual colour centre optical transitions can be compensated in situ by integrated tuning over 50 gigahertz without linewidth degradation. The ability to assemble large numbers of nearly indistinguishable and tunable artificial atoms into phase-stable PICs marks a key step towards multiplexed quantum repeaters7,8 and general-purpose quantum processors9–12.

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By engineering atomic geometries composed of nearly 1000 atomic segments embedded in micro-resonators, we observe Bragg resonances induced by the atomic lattice at the telecommunication wavelength. The geometrical arrangement of erbium atoms into a lattice inside a silicon nitride (SiN) microring resonator reduces the scattering loss at a wavelength commensurate with the lattice. We confirm dependency of light emission to the atomic positions and lattice spacing and also observe Fano interference between resonant modes in the system.

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Transition metal ions provide a rich set of optically active defect spins in wide bandgap semiconductors. Chromium (Cr⁴⁺) in silicon-carbide (SiC) produces a spin-1 ground state with a narrow, spectrally isolated, spin-selective, near-telecom optical interface. However, previous studies were hindered by material quality resulting in limited coherent control. In this work, we implant Cr into commercial 4H-SiC and show optimal defect activation after annealing above 1600 °C. We measure an ensemble optical hole linewidth of 31 MHz, an order of magnitude improvement compared to as-grown samples. An in-depth exploration of optical and spin dynamics reveals efficient spin polarization, coherent control, and readout with high fidelity (79%). We report T₁ times greater than 1 s at cryogenic temperatures (15 K) with a T₂^* = 317 ns and a T₂ = 81 μs, where spin dephasing times are currently limited by spin-spin interactions within the defect ensemble. Our results demonstrate the potential of Cr⁴⁺ in SiC as an extrinsic, optically active spin qubit.

Accurate predictions of device performance in 14-MeV neutron environments rely upon understanding the recoil cascades that may be produced. Recoils from 14-MeV neutrons impinging on both gallium nitride (GaN) and gallium arsenide (GaAs) devices were modeled and compared to the recoil spectra of devices exposed to 14-MeV neutrons. Recoil spectra were generated using nuclear reaction modeling programs and converted into an ionizing energy loss (IEL) spectrum. We measured the recoil IEL spectra by capturing the photocurrent pulses produced by single neutron interactions with the device. Good agreement, with a factor of two, was found between the model and the experiment under strongly depleted conditions. However, this range of agreement between the model and the experiment decreased significantly when the bias was removed, indicating partial energy deposition due to cascades that escape the active volume of the device not captured by the model. Consistent event rates across multiple detectors confirm the reliability of our neutron recoil detection method.

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The radiation response of TaO_x-based RRAM devices fabricated in academic (Set A) and industrial (Set B) settings was compared. Ionization damage from a ⁶⁰Co gamma source did not cause any changes in device resistance for either device type, up to 45 Mrad(Si). Displacement damage from a heavy ion beam caused the Set B in the high resistance state to decrease in resistance at 1 x 10²¹ oxygen displacements per cm³; meanwhile, the Set A devices did not exhibit any decrease in resistance due to displacement damage. Both types of devices demonstrated an increase in resistance around 3 x 10²² oxygen displacements per cm³, possibly due to damage at the oxide/metal interfaces. These extremely high levels of damage represent near-total atomic disruption, and if this level of damage were ever reached, other circuit elements would likely fail before the RRAM devices in this study. Generally, both sets of devices were much more resistant to radiation effects than other devices reported in the literature. Displacement damage effects were only observed in the Set A devices once the displacement-induced oxygen vacancies surpassed the intrinsic vacancy concentration in the devices, suggesting that high oxygen vacancy concentration played a role in the devices’ high tolerance to displacement damage.

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Color centers (defect complexes such as SiV) in diamond have shown potential in fields ranging from metrology, cybersecurity to quantum computation. Demonstrations in these fields have pushed the envelope of state-of-the-art operations – for example, single photon sources (SPS) making use of SiV centers in diamond for quantum key distribution have demonstrated all the requirements for SPS operation including: (1) stable operation with second correlation function <<1, (2) electrically driven single photon emission and (3) compatibility with frequenc y conversion to telecommunication frequencies. To-date, however, all these demonstrations have been on lab-scale one-off devices. The key question behind how to deterministically fabricate these devices, namely activation yield has been overlooked. For context, Si based semiconductor devices are hugely successful because we have a high activation yield for implanted dopants. This is not yet true for diamond color centers. As currently understood, the color center yield is dominated by a lack of vacancies in the immediate area of the implantation. We propose to optimize the activation yield of color center using a combination of (1) focused single ion implantation with in-situ detection to count the number of implanted Si ions and (2) localized point defect (vacancy) creation using a focused Li ion beam to improve the yield. These experiments build on the unique capabilities of the SNL nanoImplanter (nI) to produce focused ion beam with spatial resolution of < 10 nm of both Si and Li ions. This work will also leverage our world-leading single ion implantation and detection capabilities.

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