We synthesized up to Ge0.914Sn0.086 alloys on (100) GaAs/InyGa1−yAs buffer layers using molecular beam epitaxy. The buffer layers enable engineered control of strain in the Ge1−xSnx layers to reduce strain-related defects and precipitation. Samples grown under similar conditions show a monotonic increase in the integrated photoluminescence (PL) intensity as the Sn composition is increased, indicating changes in the bandstructure favorable for optoelectronics. We account for bandgap changes from strain and composition to determine a direct bandgap bowing parameter of b = 2.1 ± 0.1. According to our models, these are the first Ge1−xSnx samples that are both direct-bandgap and exhibit PL.

Resistance switching in TiO and many other transition metal oxide resistive random access memory materials is believed to involve the assembly and breaking of interacting oxygen vacancy filaments via the combined effects of field-driven ion migration and local electronic conduction leading to Joule heating. These complex processes are very difficult to study directly in part because the filaments form between metallic electrode layers that block their observation by most characterization techniques. By replacing the top electrode layer in a metal-insulator-metal memory structure with easily removable liquid electrolytes, either an ionic liquid (IL) with high resistance contact or a conductive aqueous electrolyte, we probe field-driven oxygen vacancy redistribution in TiO thin films under conditions that either suppress or promote Joule heating. Oxygen isotope exchange experiments indicate that exchange of oxygen ions between TiO and the IL is facile at room temperature. Oxygen loss significantly increases the conductivity of the TiO films; however, filament formation is not observed after IL gating alone. Replacing the IL with a more conductive aqueous electrolyte contact and biasing does produce electroformed conductive filaments, consistent with a requirement for Joule heating to enhance the vacancy concentration and mobility at specific locations in the film.

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The purpose of this study is to investigate anomalous redistribution of beryllium (Be) in GaAs grown by molecular beam epitaxy (MBE). A concentration-dependent diffusion coefficient for Be is found from the substitutional-interstitial diffusion model. The importance of the generation of BeI from Ga point defects (vacancies or interstitials) in the diffusion process is also presented. Extremely rapid interstitial diffusion during growth, on the order of 30 μm in 1 h at 680 °C, has also been observed. This effect begins to occur for hole concentrations above 1019/cm3. Unintentional incorporation of Be into GaAs grown after closing the Be shutter is also presented. Consideration of the surface concentration of Be during MBE growth facilitates the explanation of this memory effect.

As the R p of ion implants steadily decreases an ever-increasing percentage of the implant species lies in the oxide layer and is, therefore, not electrically active. For this reason, it is important to have analytical techniques capable of accurately measuring the thickness of ultrathin oxide layers. A round-robin study was performed on a series of SiO 2 films ranging from 0.3 to 20 nm in order to evaluate the advantages and disadvantages of five commonly used analytical techniques. High-resolution cross-section transmission electron microscopy ͑TEM͒ offers the only true measurement of oxide thickness because no density assumptions are made. In this study, TEM is used as the standard for all the other techniques. X-ray photoelectron spectroscopy and Auger electron spectroscopy offer precise measurements for ultrathin ͑Ͻ3 nm͒ films, but are limited for thicker films ͑Ͼ15 nm͒ due to the exponential decay functions that describe the sampling depth in both techniques. Secondary ion mass spectrometry ͑SIMS͒ has historically been used for characterizing relatively thick films ͑Ͼ10 nm͒ but not for thinner films because of atomic mixing effects. Encapsulating oxides with amorphous silicon prior to performing a SIMS experiment can negate these effects. A comparison of SIMS on encapsulated and as received films is made. Rutherford backscattering is an excellent technique for determining oxide thickness over a wide thickness range by channeling the Si signal from the crystalline substrate and analyzing oxygen from the amorphous oxide. Ellipsometry, being both rapid and low cost, is one of the most widely used techniques capable of accurate measurements on thick films ͑Ͼ10 nm͒.