Session N67: Defect Behavior in Extreme Environments

Thermal activation of low-density Ga implanted in Ge

Recent results have shown that quantum dots in Ge/SiGe heterostructures have high hole mobilities, long spin lifetimes, tunable g-factors, and strong spin-orbit coupling providing an intriguing alternative to silicon. In contrast to silicon, the potential for using dopants, such as Ga, as qubits in pure Ge is relatively unexplored. Further, an optical interface with dopant-spin-qubits is an exciting avenue for state readout through spin-selective bound exciton transitions, as has been observed in silicon. However, a thorough analysis of implanted Ga activation in Ge is lacking in the literature and optimal dopant density and activation are necessary for bulk optical spin detection. Here, we use spreading resistance profiling and secondary ion mass spectrometry to derive ion activation in bulk Ge implanted with Ga at 175 keV as a function of anneal temperature (T_a) and implant fluence. We show that activation is maximized near T_a = 650 ^oC and declines for T_a > 650 ^oC. Additionally, we show activation increases with implant fluence from 10% for 6x10¹⁰ cm^-2 to about 65% for 6x10¹² cm^-2. Our results guide the fabrication process towards realizing practical optical experiments and potential qubit devices.   

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Lutetium (III) oxide (Lu₂O₃) is an ultra-wide bandgap (5.5 - 5.9 eV) semiconductor that could have potential applications in optical devices operating in deep ultraviolet (UV) region. Deep UV photoluminescence (PL) spectroscopy was employed to study the optical properties of thin film and crystal powder Lu₂O₃ samples using the fourth harmonic laser (~195 nm) generated from a Ti: sapphire laser for optical excitation. Low temperature (8 K) PL spectra of the samples annealed at 800 ^oC for 1 hour in oxygen have dominant emission peak around 4.85 eV. Additionally, we observed weak PL emissions in deep UV region at 5.50 and 5.74 eV which we assumed to be band-edge emissions. The powder sample also has an emission peak at 3.61 eV. We will present the effect of annealing temperature on the PL, and power- and temperature-dependent PL measurements of the annealed Lu₂O₃ samples. We will discuss the energy diagram of Lu₂O₃ based on the observed PL and absorption measurements. Our findings on optical properties of Lu₂O₃ could have implications on its potential applications in deep UV optical devices.   

Low power Resistive Switching behavior of Cobalt/Iron Oxide Nanoparticle assembly with Symmetric Negative Differential Resistance

A resistive switching (RS) phenomena in very low power of order 1 nW is observed in an assembly of Iron Oxide nanoparticles. The samples are prepared on glass substrate using spin coating of a solution of 70.7 mM Fe(III) acetylacetonate in acetone followed by annealing at 550°C for 75 minutes in air. When Current-Voltage (I-V) characteristics is taken by sweeping the voltage in a triangular waveform of amplitude 10 V at the rate of 0.1 V/s, the device takes the low resistive state (LRS) initially going from 0 V to 10 V and at some voltage the current starts to drop sharply showing negative differential resistance (NDR) and takes high resistive state (HRS) when returning from 10 V to 0 V. The I-V curves are symmetric and highly reproducible and shows RS and NDR phenomena in the negative bias as well. The RS and symmetric NDR behavior of the device is attributed to the trapping and de-trapping of the carriers at the interface layer formed due to the interaction of oxygen vacancies and the moisture in the humid air. A solution of 70.1 mM of Co(III) acetylacetonate in acetone is mixed into the previous solution, where the inclusion of Co increases the ratio of HRS/LRS to ~150%. The improvement in the HRS/LRS may be due to the higher reactivity of Cobalt, which, in turn, increases the density of oxygen vacancies in Iron oxide. For all samples, a ratio of HRS/LRS >7 was achieved in both positive and negative bias regions.   

Atomic Focused Nitrogen Ion Beam from a Liquid-Metal Alloy Ion Source

Focused ion beam (FIB) implantation is a popular technique in the fabrication of optically active color centers. The nanometer scale resolution of FIB implantation allows targeting of photonic structures for scalable fabrication of color centers. The nitrogen-vacancy (NV) in diamond has been shown to be an extremely sensitive magnetic field sensor and recent results have measured magnetic fields in record low volume through integration of NV with AFM tips. A scalable FIB source for localized implantation of nitrogen (N) has not yet been demonstrated but is a critical component in nanometer resolution placement of NVs for quantum applications.

We have made and characterized a FIB N source based on a AuSn liquid metal alloy ion source eutectic that will enable scalable fabrication of localized NVs. We add N to the foil, which is then released during field emission, by implanting thin AuSn foils with 200 keV N⁺⁺. We confirm inclusion of N through elastic recoil detection and release of N⁺ and N⁺⁺ ions during operation of the source using ion beam induced charge collection measurements. We will report on the source characteristics including beam current, lifetime (approximately 200 µAh), stability and spot size.

SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525   

Far-infrared and annealing studies of thermal donors in high-purity silicon

We have measured the temperature-dependent infrared transmission of high-purity silicon samples having impurity concentrations of ~10¹⁵ /cm³. Measurements were made in a frequency range from 10–10,000 cm^-1 at temperatures from 10–300 K. At 10 K, silicon is transparent in the far infrared (10–600 cm^-1) apart from narrow absorption lines caused by residual oxygen impurities known as thermal double donors (TDD). At higher temperatures, the electrons are ionized by the thermal energy in the crystal and become free electrons, causing a Drude-like response in the far infrared. There is also absorption caused by several vibrational modes of Si₂O in the far and mid infrared regions. The oxygen is introduced by the amorphous silica crucible during the Czochralski growth process and occurs as an uneven distribution of oxygen throughout the boule. Samples were annealed between 450-700 C in vacuum and a significant effect on the TDD oxygen but not on the vibrational oxygen concentration was observed. This leads us to believe that the thermal history of the boule plays an important role in determining the structure of the oxygen impurity.