ハイペロン-陽子散乱実験に向けた円筒形飛跡検出器・カロリメータシステム“CATCH”の開発と利用

Tohoku University田村裕和課

Control of plasma-CVD SiO2/InAlN interface by N2O plasma oxidation

Control of the plasma-CVD SiO2/InAlN interface by N2O plasma oxidation of the InAlN surface was studied. The interface was characterized by both X-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurement of metal-insulator-semiconductor (MIS) diodes. An excessively long duration of oxidation led to the deterioration of the stoichiometry of the InAlN surface and plasma oxide, resulting in a high-density of interface states in the completed MIS diodes. Meanwhile, the surface-localized oxygen deficiency in the plasma oxide layer was observed by XPS. The intensity ratio of the oxygen-deficient component to the fully oxidized component in the O 1s spectrum decreased with increasing oxidation duration. Consequently, there was an optimum oxidation duration. The interface state density was reduced by almost one order in the case of plasma oxidation for an appropriate duration compared with the case of the direct deposition of SiO2 onto InAlN. (C) 2019 The Japan Society of Applied Physic

Formation of thermally grown SiO2/GaN interface

An attempt was made to form a thermally grown SiO2/GaN interface. A Si layer deposited on the c-plane GaN surface was oxidized in an O-2 atmosphere to form a SiO2 layer. The formation of SiO2 with a bandgap of 8.6 eV was confirmed by x-ray photoelectron spectroscopy. Metal-oxide-semiconductor diodes were fabricated and tested to characterize the interface by electrical measurements. The capacitance-voltage (C-V) characteristics measured at 1 MHz showed that a longer oxidation time resulted in a steeper slope. However, it was unavoidable that a bump in a C-V curve appeared after a long oxidation time. The electron trap distributions derived from C-V curves exhibited a discrete-level trap at 0.7 eV from the conduction band edge. This discrete-level trap was an acceptor-like trap that can be assigned to a Ga vacancy. An insufficient oxidation led to a high leakage current owing to the asperities of the residual polycrystalline Si layer. Although the leakage current was improved by extending the oxidation time, an excessively long oxidation time resulted in a slight increase in the leakage current. We cannot deny the possibility of the diffusion of Ga atoms into SiO2 during oxidation. Moreover, the cross-sectional transmission electron microscopy and energy-dispersive x-ray spectroscopy of a sample formed with an excessively long oxidation time indicated the formation of a Ga oxide interlayer without a severe disorder. Most possibly, the formation of the Ga oxide interlayer by excess oxidation improved the interface properties

Detection of defect levels in vicinity of Al₂O₃/p-type GaN interface using sub-bandgap-light-assisted capacitance-voltage method

Defect levels in the vicinity of the Al2O3/p-type GaN interface were characterized using a sub-bandgap-light-assisted capacitance-voltage (C-V) method. For metal-oxide-semiconductor (MOS) diodes prepared using p-type GaN (p-GaN) and Al2O3 formed by atomic layer deposition, the C-V curves measured in the dark showed capacitance saturation at a negative bias and a large negative voltage shift compared with ideal curves, which implied the effects of donor-like gap states in the vicinity of the Al2O3/p-GaN interface. Upon illumination with monochromated sub-bandgap light with photon energies higher than 2.0 eV under a large positive bias, the subsequently measured C-V curves showed three plateaus. The plateau under the positive bias voltage due to the surface inversion appeared despite the sub-bandgap illumination, which did not appear at 1.8 eV light illumination, indicating the existence of midgap defect levels. Moreover, the other plateaus were attributed to defect levels at 0.60 and 0.7-0.8 eV above the valence band maximum. For a sample whose surface was prepared by photo-electrochemical (PEC) etching to a depth of 16.5 nm, the C-V curve measured in the dark showed a reduced voltage shift compared with the unetched sample. Furthermore, sub-bandgap-light-assisted C-V curves of the sample with PEC etching showed no plateau at a positive bias, which indicated the reduction in the density of the midgap defect states. Possible origins of the detected defect levels are discussed. The obtained results showed that the interface control can improve the properties of p-GaN MOS structures. Published under an exclusive license by AIP Publishing

Detection of defect levels in vicinity of Al₂O₃/p-type GaN interface using sub-bandgap-light-assisted capacitance-voltage method

Defect levels in the vicinity of the Al2O3/p-type GaN interface were characterized using a sub-bandgap-light-assisted capacitance-voltage (C-V) method. For metal-oxide-semiconductor (MOS) diodes prepared using p-type GaN (p-GaN) and Al2O3 formed by atomic layer deposition, the C-V curves measured in the dark showed capacitance saturation at a negative bias and a large negative voltage shift compared with ideal curves, which implied the effects of donor-like gap states in the vicinity of the Al2O3/p-GaN interface. Upon illumination with monochromated sub-bandgap light with photon energies higher than 2.0 eV under a large positive bias, the subsequently measured C-V curves showed three plateaus. The plateau under the positive bias voltage due to the surface inversion appeared despite the sub-bandgap illumination, which did not appear at 1.8 eV light illumination, indicating the existence of midgap defect levels. Moreover, the other plateaus were attributed to defect levels at 0.60 and 0.7-0.8 eV above the valence band maximum. For a sample whose surface was prepared by photo-electrochemical (PEC) etching to a depth of 16.5 nm, the C-V curve measured in the dark showed a reduced voltage shift compared with the unetched sample. Furthermore, sub-bandgap-light-assisted C-V curves of the sample with PEC etching showed no plateau at a positive bias, which indicated the reduction in the density of the midgap defect states. Possible origins of the detected defect levels are discussed. The obtained results showed that the interface control can improve the properties of p-GaN MOS structures. Published under an exclusive license by AIP Publishing

Main causes of death in advanced biliary tract cancer

Abstract Background There are no previous reports on the main causes of death in biliary tract cancer (BTC) patients. This study aimed to evaluate the main causes of death and survival rates in patients with BTC. Methods We retrospectively evaluated 143 patients who were diagnosed with unresectable BTC between August 2010 and March 2020. We classified the main causes of death based on laboratory data, imaging studies, and medical records. The main causes of death evaluated included liver failure, cholangitis, cachexia, other causes associated with tumor progression, and complications. We also analyzed survival rates for each main cause of death. Results After excluding patients who were lost to follow‐up, living patients, and patients who had no records of laboratory data within 30 days before the date of death, 108 patients were analyzed. The main cause of death was cholangitis in 33 (30.6%), cachexia in 22 (20.4%), liver failure in 10 (9.3%), other causes associated with tumor progression in 18 (16.7%), and complications in 25 (23.2%) patients. Median overall survival (OS) was 334.0 days in the chemotherapy group and 75.0 days in the best supportive care (BSC) group. Survival analyzed according to the main cause of death was significantly different between the chemotherapy and BSC groups; OS for cachexia, cholangitis, liver failure, other causes associated with tumor progression, and complications, respectively, were 453.0, 499.0, 567.0, 205.0, and 327.5 days (p = 0.003) in the chemotherapy group and 219.0, 69.0, 34.0, 93.0, and 56.0 days (p = 0.001) in the BSC group. Conclusion The main causes of death in patients with advanced BTC are cholangitis, cachexia, liver failure, other causes associated with tumor progression, and complications. Other causes associated with tumor progression in the chemotherapy group, and liver failure in the BSC group as the main causes of death shortened the survival of BTC patients