Homoepitaxial growth of β-Ga2O3 using metalorganic vapor-phase epitaxy (MOVPE) on several different crystal orientations has previously been studied, but growth on the (2¯01) plane has remained comparatively unexplored. To investigate this, we grew Si-doped and unintentionally doped (UID) homoepitaxial layers simultaneously on Sn-doped (2¯01) and (010) substrates under conditions optimized for (010) growth. We report herein on results from current–voltage and capacitance–voltage (IV and CV) and deep level transient spectroscopy (DLTS) characterization of Schottky diodes fabricated on these samples. Devices on (010) display nearly ideal Schottky diode JV and CV behaviors while for (2¯01) evidence of complete depletion of >2 μm thickness, UID epilayers are observed. The (2¯01) UID diodes exhibited Mott–Gurney space charge-limited transport and were completely depleted even at zero bias. Doping (2¯01) samples heavily with Si was sufficient to overcome background compensation and reproduce near-ideal diode behavior. DLTS data from these doped devices show, in addition to typical negative majority-carrier transients, positive transients with a broad energy distribution, possibly indicating traps on structural defects or surface states. An etch pit analysis under SEM revealed intricate structures of the grown layers. Cross-sectional TEM characterization of a (2¯01) sample revealed a high density of structural defects within the epitaxial layer, likely stacking faults. Hypotheses for the origins of the compensation in (2¯01) β-Ga2O3 homoepitaxial MOVPE growth under (010) growth conditions are discussed; the most likely explanation is the presence of defect states introduced by the stacking faults visible under TEM.

We present new H I spectral line images of the nearby low-mass galaxy NGC 5238, acquired with the Karl G. Jansky Very Large Array (VLA a ). Located at a distance of 4.51 ± 0.04 Mpc, NGC 5238 is an actively star-forming galaxy with widespread Hα and UV continuum emission. The source is included in many ongoing and recent nearby galaxy surveys, but until this work the spatially resolved qualities of its neutral interstellar medium have remained unstudied. Our H I images resolve the disk on physical scales of ∼400 pc, allowing us to undertake a detailed comparative study of the gaseous and stellar components. The H I disk is asymmetric in the outer regions, and the areas of high H I mass surface density display a crescent-shaped morphology that is slightly offset from the center of the stellar populations. The H I column density exceeds 10 21 cm −2 in much of the disk. We quantify the degree of co-spatiality of dense H I gas and sites of ongoing star formation as traced by far-UV and Hα emission. The neutral gas kinematics are complex; using a spatially-resolved positionvelocity analysis, we infer a rotational velocity of 31 ± 5 km s −1 . We place NGC 5238 on the baryonic Tully-Fisher relation and contextualize the system amongst other low-mass galaxies.

Centimeter-wave transitions are important counterparts to the rotational mm-wave transitions usually observed to study gas in star-forming regions. However, given their relative weakness, these transitions have historically been neglected. We present Australia Telescope Compact Array 4cm-and 15mm-band spectral line observations of nine nearby star-forming galaxies in the H75 array configuration. Thirteen different molecular lines are detected across the sample from OH, NH 3 , H 2 O, H 2 CO, and c-C 3 H 2 , as well as 18 radio recombination lines (RRLs) in NGC 253. Excited OH 2 Π 3/2 absorption is detected towards NGC 253 (J=5/2), NGC 4945 (J=9/2), and Circinus (J=9/2); the latter two represent only the third and fourth extragalactic J=9/2 detections. These lines in Circinus suggest rotation temperatures in excess of 2000 K, and thus it is likely that the populations of OH rotational states are not governed by a Boltzmann distribution. Circinus's OH lines are blueshifted from the systemic velocity by~35 km s −1 , while NGC 4945's are redshifted by~100 km s −1 . NGC 4945's OH absorption likely indicates infall onto the nucleus. The NH 3 (1,1) through (6,6) lines in NGC 4945 display a superposition of emission and absorption similar to that seen in other dense gas tracers. Strong (3,3) emission points towards maser activity. The relative NH 3 absorption strengths in NGC 4945 show similar anomalies as in previous studies of Arp 220 (weak (1,1) and strong (5,5) absorption). A trend towards higher LTE electron temperatures with increasing RRL frequency is present in NGC 253, likely indicative of stimulated emission within the nuclear region.