The impact of C incorporation on the deep level spectrum of n-type and semi-insulating GaN:C:Si films grown by rf plasma-assisted molecular-beam epitaxy (MBE) was investigated by the combination of deep level transient spectroscopy, steady-state photocapacitance, and transient deep level optical spectroscopy. The deep level spectra of the GaN:C:Si samples exhibited several band-gap states. A monotonic relation between systematic doping with C and quantitative trap concentration revealed C-related deep levels. A deep acceptor at Ec−2.05eV and a deep donor at Ec−0.11eV are newly reported states, and the latter is the first directly observed deep level attributed to the CGa defect. A configuration-coordinate model involving localized lattice distortion revealed strong evidence that C-related deep levels at Ec−3.0eV and Eν+0.9eV are likely identical and associated with the yellow luminescence in C-doped GaN films. Of the deep levels whose trap concentration increase with C doping, the band-gap states at Ec−3.0 and 3.28eV had the largest concentration, implying that free-carrier compensation by these deep levels is responsible for the semi-insulating behavior of GaN:C:Si films grown by MBE. The differing manner by which C incorporation in GaN may impact electrical conductivity in films grown by MBE and metal-organic chemical-vapor deposition is discussed.

The effect of excess C incorporation on the deep level spectrum of n-type GaN grown by metalorganic chemical vapor deposition was investigated. Low-pressure (LP) growth conditions were used to intentionally incorporate excess C compared to atmospheric pressure (AP) growth conditions. GaN samples with high C content are found to be highly resistive, and samples codoped with C and Si are heavily compensated. From a comparison of deep level optical spectroscopy and deep level transient spectroscopy measurements of the LP-grown codoped GaN:C:Si sample with the AP-grown unintentionally doped GaN, two deep levels at Ec−Et=1.35 and 3.28 eV are observed to have a direct relation to excess C incorporation. Comparing these activation energies to previous theoretical studies strongly suggests that the levels may be associated with a C interstitial and CN defect, respectively. These results suggest that C forms not only a shallow acceptor level but also a deep acceptor level in GaN, and these levels contribute to the compensation of the free carriers in n-type GaN:C.

Solar-blind photodetection and photoconductive gain >50 corresponding to a responsivity >8 A/W were observed for β-Ga2O3 Schottky photodiodes. The origin of photoconductive gain was investigated. Current-voltage characteristics of the diodes did not indicate avalanche breakdown, which excludes carrier multiplication by impact ionization as the source for gain. However, photocapacitance measurements indicated a mechanism for hole localization for above-band gap illumination, suggesting self-trapped hole formation. Comparison of photoconductivity and photocapacitance spectra indicated that self-trapped hole formation coincides with the strong photoconductive gain. It is concluded that self-trapped hole formation near the Schottky diode lowers the effective Schottky barrier in reverse bias, producing photoconductive gain. Ascribing photoconductive gain to an inherent property like self-trapping of holes can explain the operation of a variety of β-Ga2O3 photodetectors.

Contrast medium-enhanced pulmonary CT angiography (CTA) is increasingly used as the first-line imaging test in suspected PE and is available 24 hours a day at most institutions [10][11][12][13][14]. Pulmonary CTA not only allows direct visualization of emboli but provides information regarding the status of the right heart [15,16]. In several studies, the ratio of the RV to left ventricle (LV) diameters on pulmonary CTA has been proposed as a sign for RV dysfunction [17][18][19]. Other signs have been described, including bowing of the interventricular septum and reflux of contrast medium into the inferior vena cava (IVC) [20,21]. However, a variety of different methods for the quantitative assessment of RV dysfunction on pulmonary CTA have been proposed [17][18][19][20][21][22][23][24] and the literature shows variable results for the prognostic power of pulmonary CTA signs of RV dysfunction to predict adverse outcomes. This variability may in part be explained by the somewhat subjective nature of diagnosing RV dysfunction on pulmonary CTA because formal criteria for es- AJR 2010; 194:1500-1506 0361-803X/10/1946-1500 © American Roentgen Ray Society A cute pulmonary embolism (PE) is a common disease with a 3-month mortality rate of up to 17.4% [1][2][3][4]. Even if PE is properly treated with anticoagulation, the mortality rate in hemodynamically stable patients varies from 8.1% to 15.1% [4,5]. Death is usually caused by acute right heart failure [4][5][6][7][8][9]. Acute PE increases the pressure of the pulmonary arterial system and right ventricle (RV) resulting in RV dysfunction, which may progress to right heart failure and circulatory collapse [5,6]. Patients with RV dysfunction have a higher mortality rate than those without, even if they are initially hemodynamically stable [6,7]. Thus, the presence of RV dysfunction is a marker for adverse clinical outcome in patients with acute PE [6][7][8]. Echocardiography is the most common first-line examination to diagnose the signs of RV dysfunction [6][7][8][9]. However, this test has limited off-hour availability at many institutions, and occasionally the RV may be difficult to image with the trans thoracic approach. OBJECTIVE. The purpose of our study was to determine the interobserver reproducibility of CT findings of right ventricular (RV) dysfunction in pulmonary embolism (PE). Reproducibility of CT C a r d io p u lm o n a r y I m ag i ng • O r ig i n a l R e s e a rc hMATERIALS AND METHODS. Two experienced observers independently and retrospectively evaluated pulmonary CT angiography (CTA) studies of 50 patients with acute PE for the following signs: bowing of the interventricular septum, inferior vena cava (IVC) contrast medium reflux, RV diameter (RVD)/left ventricular diameter (LVD) ratio on axial sections and four-chamber (4-CH) views, and RV volume (RVV)/left ventricular volume (LVV) ratio. Analysis used kappa statistics, Spearman's rank correlation, and Bland-Altman statistics.RESULTS. The two observers had fair to moderate agreement (κ = 0.32-0.44)...

Low p-type conductivity and high contact resistance remain a critical problem in wide band gap AlGaN-based ultraviolet light emitters due to the high acceptor ionization energy. In this work, interband tunneling is demonstrated for non-equilibrium injection of holes through the use of ultra-thin polarization-engineered layers that enhance tunneling probability by several orders of magnitude over a PN homojunction. Al 0.3 Ga 0.7 N interband tunnel junctions with a low resistance of 5.6×10 -4 Ω cm 2 were obtained and integrated on ultraviolet light emitting diodes. Tunnel injection of holes was used to realize GaN-free ultraviolet light emitters with bottom and top n-type Al 0.3 Ga 0.7 N contacts. At an emission wavelength of 327 nm, stable output power of 6 W/cm 2 at a current density of 120 A/cm 2 with a forward voltage of 5.9 V was achieved. This demonstration of efficient interband tunneling introduces a new paradigm for design of ultraviolet light emitting diodes and diode lasers, and could enable higher efficiency and lower cost ultraviolet emitters.