Deep-Level Traps Responsible for Persistent Photocurrent in Pulsed-Laser-Deposited β-Ga2O3 Thin Films

Gallium oxide (β-Ga2O3) is emerging as a promising wide-bandgap semiconductor for optoelectronic and high-power electronic devices. In this study, deep-level defects were investigated in pulsed-laser-deposited epitaxial films of β-Ga2O3. A deep ultraviolet photodetector (DUV) fabricated on β-Ga2O3 film showed a slow decay time of 1.58 s after switching off 250 nm wavelength illumination. Generally, β-Ga2O3 possesses various intentional and unintentional trap levels. Herein, these traps were investigated using the fractional emptying thermally stimulated current (TSC) method in the temperature range of 85 to 473 K. Broad peaks in the net TSC curve were observed and further resolved to identify the characteristic peak temperature of individual traps using the fractional emptying method. Several deep-level traps having activation energies in the range of 0.16 to 1.03 eV were identified. Among them, the trap with activation energy of 1.03 eV was found to be the most dominant trap level and it was possibly responsible for the persistent photocurrent in PLD-grown β-Ga2O3 thin films. The findings of this current work could pave the way for fabrication of high-performance DUV photodetectors.

Characterization of Spatial Distribution of Trap Across the Substrate in Metal-Insulator-Semiconductor Structure with Band Bending Effect

We report the technique of trap distribution extraction according to the vertical position of the substrate in the p-MOSFET. This study was conducted on a single device. This technique is an experimental method. Ctrap was extracted based on the deep depletion C–V characteristics. In VFB, the trap level is neutral. When bias is applied, the energy band bends, resulting in modulation of the quasi-Fermi level. The area created by the bending of the energy band is equal to the area created by the Fermi level modulation. The trap level existing in this area becomes charged. Considering this, the spatial distribution of Trap was extracted. The trap extracted by the proposed method has a maximum value at the interface, rapidly decreases, and is distributed up to 8 nm in the vertical direction. The study of trap spatial distribution is expected to be applicable to the separation of trap interface state and bulk trap extraction later.

Photoresponse properties of Au/(CoFe2O4-PVP)/n-Si/Au (MPS) diode

Photo-response properties of the Au/(CoFe2O4-PVP)/n-Si (MPS) diode were investigated using current-voltage (I-V) measurements achieved under dark and various illumination conditions. The experimental results showed that the MPS diode has a good response to the illumination. Especially, in reverse-bias region, photocurrent (Iph) increases with increasing illumination intensity (P) due to the formation of electron–hole pairs. The double-logarithmic Iph-P plot has a good relation with 1.27 slope and such high value of slope indicates a lower density of the unoccupied trap level. This indicates that the diode exhibits a good photoconductive and photovoltaic behavior. The photo-to-dark current ratio confirms the photo-sensitivity of the diode. Thermionic emission (TE) theory was used to determine the diode electronic parameters such as saturation current (I0), ideality factor (n) and barrier height (ΦB0) and their values were calculated from the measured I-V data. Moreover, the ΦB0 and series resistance (Rs) were extracted from an alternative method suggested by Norde. All these parameters (ΦB0, n, Rs, and I0) decrease with increasing illumination intensity and there is a good linear correlation between ΦB0 and n as ΦB0 (n) = 4.72x10− 2n + 0.5464 eV. As a results, the fabricated MPS diode due to the excellent photo-response can be used for photovoltaic applications.

Characterization of Macrophages and Osteoclasts in the Osteosarcoma Tumor Microenvironment at Diagnosis: New Perspective for Osteosarcoma Treatment?

Biological and histopathological techniques identified osteoclasts and macrophages as targets of zoledronic acid (ZA), a therapeutic agent that was detrimental for patients in the French OS2006 trial. Conventional and multiplex immunohistochemistry of microenvironmental and OS cells were performed on biopsies of 124 OS2006 patients and 17 surgical (“OSNew”) biopsies respectively. CSF-1R (common osteoclast/macrophage progenitor) and TRAP (osteoclast activity) levels in serum of 108 patients were correlated to response to chemotherapy and to prognosis. TRAP levels at surgery and at the end of the protocol were significantly lower in ZA+ than ZA− patients (padj = 0.0011; 0.0132). For ZA+-patients, an increase in the CSF-1R level between diagnosis and surgery and a high TRAP level in the serum at biopsy were associated with a better response to chemotherapy (p = 0.0091; p = 0.0251). At diagnosis, high CD163+ was associated with good prognosis, while low TRAP activity was associated with better overall survival in ZA− patients only. Multiplex immunohistochemistry demonstrated remarkable bipotent CD68+/CD163+ macrophages, homogeneously distributed throughout OS regions, aside osteoclasts (CD68+/CD163−) mostly residing in osteolytic territories and osteoid-matrix-associated CD68−/CD163+ macrophages. We demonstrate that ZA not only acts on harmful osteoclasts but also on protective macrophages, and hypothesize that the bipotent CD68+/CD163+ macrophages might present novel therapeutic targets.