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Plasma enhanced atomic layer deposition (PEALD) is a cyclic atomic layer deposition process that incorporates plasma-generated species into one of the cycle substeps. The addition of plasma is advantageous as it generally provides unique gas-phase chemistries and a substantially reduced growth temperature compared to thermal approaches. However, the inclusion of plasma, coupled with the increasing variety of plasma sources used in PEALD, can make these systems challenging to understand and control. This work focuses on the use of plasma diagnostics to examine the plasma characteristics of a hollow cathode enhanced capacitively coupled plasma (HC-CCP) source, a type of plasma source that has seen increasing attention in recent years for PEALD. Ultraviolet to near-infrared spectroscopy as well as spatially resolved Langmuir probe and emissive probe measurements are employed to characterize an HC-CCP plasma source using nitrogen based gas chemistries typical of nitride PEALD processes. Spectroscopy is used to characterize the relative concentrations of important reactive and energetic neutral species generated in HC-CCP systems as a function of applied RF power, gas chemistry, and pressure. In addition, the electron energy distribution function, electron temperature, plasma potential, and plasma density for the same process parameters are examined using an RF compensated Langmuir probe and emissive probe. These measurements indicated that electron temperature (Te), electron density (ne), and plasma potential (Vp) varied significantly over the operating conditions examined with Te varying from 1.5 to 8 eV, Vp varying from 30 to 90 V, and ne varying between 1015 and low 1016 m−3. This wide range of plasma conditions is mediated by a mode transition from a low Te, high ne mode of operation at low pressure (<100 mTorr) to a high Te, low ne mode at higher pressures (>100 mTorr). These operational modes appear analogous to the classical γ and α modes of traditional capacitively coupled plasmas. Atomic N and H densities also vary significantly over the operating conditions examined. [ABSTRACT FROM AUTHOR]

Planar thin film β-Ga2O3 photodetectors were irradiated with 5 MeV protons at doses from 1013 to 1015cm-2, and the resulting effects on photocurrent, responsivity, quantum efficiency, and photo-to-dark current ratio at 254 nm wavelength were measured at both 25 and 150°C. The photocurrent increased with dose due to the introduction of damage from nonionizing energy loss by the protons. The total calculated vacancy concentration increased from 5×1015 to 5×1017 cm-3 over the dose range investigated. The dark current increased in proportion with the implant dose, leading to a decrease in the ratio of photocurrent to dark current. The photocurrent induced by 254 nm illumination increased with dose, from~0.3×10-7 A at 25°C for a dose of 1013cm-2 to ~10-6 A at a dose of 1015cm-2 at a fixed light intensity of 760 μW/cm². The phototo- dark current ratio decreased from ~60 in the control samples to ~9 after proton doses of 1015cm-2, with corresponding external quantum efficiencies of ~10³% in control samples, ~2×10³% for a dose of 1013cm-2, and 104% for a dose of 1015cm-2. The mechanism for the increase in photocurrent is the introduction of gap states, since the dark current of the photodetectors was increased by illuminating with sub-bandgap (red or green laser light) for the proton irradiated samples. [ABSTRACT FROM AUTHOR]

The temperature dependent photoresponse of planar photodetectors fabricated on β-Ga2O3 films grown on Al2O3 by metalorganic chemical vapor deposition to 254 nm wavelength, and blindnessto 365 nm light, are reported over the range of 25-350 °C. Ohmic contacts were formed by Siimplantationand annealing at 900 °C, followed by deposition of Ti/Au metallization. The photocurrentinduced by 254 nm illumination increased monotonically with temperature, from 2.5 ~10-7A at 25°C to ~2.2 ~10-6 A at 350 °C at a fixed 254 nm light intensity of 760 μW/cm². The photosensitivitydecreases at high temperatures in many photoconductors (thermal quenching), in sharpcontrast to the photosensitivity increase with high temperatures in this study. This is ascribed to thepresence of states in the gap of Ga²O³, whose presence was proven by exposure to below band-gapenergy. In this case, the current still increased due to the presence of defect levels in the band gapand the generation of photocurrent is due to a transition between the valence or conduction bandand impurity or defect levels within the band gap. The temperature dependent photo-to-dark currentratio for this wavelength was 328 at room temperature and decreased to ~9 at 350 °C. The responsivityincreased from 5 to 36 A/W over this temperature range, with corresponding external quantumefficiencies of 2.5 ~ 10³% at 25°C and 1.75 ~ 104% at 350 °C. Similarly large numbersreported for Ga2O3 photodetectors have previously been ascribed to carrier multiplication effects. [ABSTRACT FROM AUTHOR]

The surface preparation for depositing Al2O3 for fabricating Au/Ni/Al2O3/n-GaN (0001) metal oxide semiconductor (MOS) capacitors was optimized as a step toward realization of high performance GaN MOSFETs. The GaN surface treatments studied included cleaning with piranha (H2O2:H2SO4=1:5), (NH4)2S, and 30% HF etches. By several metrics, the MOS capacitor with the piranha-etched GaN had the best characteristics. It had the lowest capacitance-voltage hysteresis, the smoothest Al2O3 surface as determined by atomic force microscopy (0.2nm surface roughness), the lowest carbon concentration (∼0.78%) at the Al2O3/n-GaN interface (from x-ray photoelectron spectroscopy), and the lowest oxide-trap charge (QT = 1.6×1011cm-2eV-1). Its interface trap density (Dit=3.7×1012cm-2eV-1), as measured with photon-assisted capacitance-voltage method, was the lowest from conduction band-edge to midgap. [ABSTRACT FROM AUTHOR]

The driven electrode is a circular stainless steel plate (diameter = 64 mm, thickness 5 cm) that includes a 3 × 3 array of 10 mm diameter through-holes (the "hollow cathodes"). The hollow cathode enhanced capactively coupled plasma system studied in this work was supplied by Meaglow Ltd. (circa 2013). Erratum: "Hollow cathode enhanced capacitively coupled plasmas in Ar/N2/H2 mixtures and implications for plasma enhanced ALD" [J. Vac. [Extracted from the article]

Periodically oriented GaN surfaces have been investigated using scanning probe microscopy techniques to compare Ga- and N-polar regions on a common surface. An epitaxial layer comprising 16 μm-wide stripes of alternating surface polarity was grown by utilizing a patterned AlN layer on an N-polar GaN template. The regions of different polarity are easily distinguishable in atomic force microscopy (AFM) images, with the Ga-polar stripes, which nucleate on the patterned AlN regions being approximately 300 nm higher than the adjacent N-polar stripes. In addition, local surface potential measurements using scanning Kelvin probemicroscopy (SKPM) indicate that the N-polar regions are 0.2 to 0.5 eV higher in potential compared to Ga-polar ones, with lower surface potential contrast occurring after an HCl-based surface treatment. Using conductive AFM, electrons were injected into the surface to probe the surface charging behavior in dark. Only the N-polar regions demonstrated significant localized charging, where changes of over 1.5 eV were seen in SKPM images taken immediately after charging. This behavior was appreciably decreased by an HCl treatment, suggesting that a surface oxide in the N-polar regions plays a significant role in the charging behavior. In addition, the local surface photovoltage (SPV) was measured using above-bandgap illumination. The N-polar regions demonstrate a higher steady-state SPV value and a significantly slower restoration behavior as compared to the Ga-polar regions. The authors therefore find that several characterization techniques can readily distinguish the Ga- versus N-polar regions on this periodically oriented surface. [ABSTRACT FROM AUTHOR]