Elektrik-Elektronik Mühendisliği BölümüElektrik-Elektronik Mühendisliği Bölümünü içerir.http://hdl.handle.net/20.500.11787/862024-03-28T13:22:36Z2024-03-28T13:22:36ZInvestigation of thermally evaporated high resistive B-doped amorphous selenium alloy films and metal contact studiesOner, CihanNguyen, Khai V.Pak, Rahmi O.Mohammad, A. MannanMandal, Krishna C.http://hdl.handle.net/20.500.11787/83562023-12-21T06:47:32Z2015-01-01T00:00:00ZInvestigation of thermally evaporated high resistive B-doped amorphous selenium alloy films and metal contact studies
Oner, Cihan; Nguyen, Khai V.; Pak, Rahmi O.; Mohammad, A. Mannan; Mandal, Krishna C.
Amorphous selenium (a-Se) alloy materials with arsenic, chlorine, boron, and lithium doping were synthesized for room temperature nuclear radiation detector applications using an optimized alloy composition for enhanced charge transport properties. A multi-step synthetic process has been implemented to first synthesize Se-As and Se-Cl master alloys from zone-refined Se (~ 7N), and then synthesized the final alloys for thermally evaporated large-area thin-film deposition on oxidized aluminum (Al/Al2O3) and indium tin oxide (ITO) coated glass substrates. Material purity, morphology, and compositional characteristics of the alloy materials and films were examined using glow discharge mass spectroscopy (GDMS), inductively coupled plasma mass spectroscopy (ICP-MS), differential scanning calorimetry (DSC), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive analysis by x-rays (EDAX). Current-Voltage (I-V) measurements were carried out to confirm very high resistivity of the alloy thin-films. We have further investigated the junction properties of the alloy films with a wide variety of metals with different work functions (Au, Ni, W, Pd, Cu, Mo, In, and Sn). The aim was to investigate whether the choice of metal can improve the performance of fabricated detectors by minimizing the dark leakage current. For various metal contacts, we have found significant dependencies of metal work functions on current transients by applying voltages from -800 V to +1000 V.
2015-01-01T00:00:00ZHigh-barrier Schottky contact on n-type 4H-SiC epitaxial layer and studies of defect levels by deep level transient spectroscopy (DLTS)Nguyen, Khai V.Pak, Rahmi O.Oner, CihanMohammad, A. MannanMandal, Krishna C.http://hdl.handle.net/20.500.11787/83552023-12-21T06:47:06Z2015-01-01T00:00:00ZHigh-barrier Schottky contact on n-type 4H-SiC epitaxial layer and studies of defect levels by deep level transient spectroscopy (DLTS)
Nguyen, Khai V.; Pak, Rahmi O.; Oner, Cihan; Mohammad, A. Mannan; Mandal, Krishna C.
High barrier Schottky contact has been fabricated on 50 μm n-type 4H-SiC epitaxial layers grown on 350 μm thick substrate 8° off-cut towards the [11̅20] direction. The 4H-SiC epitaxial wafer was diced into 10 x 10 mm2 samples. The metal-semiconductor junctions were fabricated by photolithography and dc sputtering with ruthenium (Ru). The junction properties were characterized through current-voltage (I-V) and capacitance-voltage (C-V) measurements. Detectors were characterized by alpha spectroscopy measurements in terms of energy resolution and charge collection efficiency using a 0.1 μCi 241Am radiation source. It was found that detectors fabricated from high work function rare transition metal Ru demonstrated very low leakage current and significant improvement of detector performance. Defect characterization of the epitaxial layers was conducted by deep level transient spectroscopy (DLTS) to thoroughly investigate the defect levels in the active region. The presence of a new defect level induced by this rare transition metal-semiconductor interface has been identified and characterized.
2015-01-01T00:00:00ZSurface passivation and isochronal annealing studies on n-type 4H-SiC epitaxial layerMohammad, A. MannanNguyen, Khai V.Pak, Rahmi O.Oner, Cihanhttp://hdl.handle.net/20.500.11787/83542023-12-21T06:46:45Z2015-01-01T00:00:00ZSurface passivation and isochronal annealing studies on n-type 4H-SiC epitaxial layer
Mohammad, A. Mannan; Nguyen, Khai V.; Pak, Rahmi O.; Oner, Cihan
Schottky barrier radiation detectors were fabricated on the Si-face of 50 μm thick detector grade n-type 4H-SiC epitaxial layers. The junction properties of the fabricated detectors were investigated by current-voltage (I-V) and capacitancevoltage (C-V) measurements. The radiation detector performances were evaluated by alpha pulse height spectroscopy using a 0.1 μCi 241Am radiation source. Deep level transient spectroscopy (DLTS) measurements were carried out to identify and characterize the electrically active defect levels present in the epitaxial layers. The performance of the detector was found to be limited by the presence of electrically active defect centers in the epilayer. Deep level defects were reduced significantly by isochronal annealing. Surface passivation studies were conducted on n-type 4H-SiC epilayers for use on radiation detectors for the first time. Energy resolution of the detector was found to have improved after passivation and the life time killing defects that were responsible for preventing full charge collection were reduced significantly. Systematic and thorough C-DLTS studies were conducted prior and subsequent to isochronal annealing to observe evolution of the deep level defects.
2015-01-01T00:00:00ZDefect characterization of Cd0.9Zn0.1Te crystals using electron beam induced current (EBIC) imaging and thermally stimulated current (TSC) measurementsPak, Rahmi O.Nguyen, Khai V.Oner, CihanMohammad, A. MannanMandal, Krishna C.http://hdl.handle.net/20.500.11787/83532023-12-21T06:46:23Z2015-01-01T00:00:00ZDefect characterization of Cd0.9Zn0.1Te crystals using electron beam induced current (EBIC) imaging and thermally stimulated current (TSC) measurements
Pak, Rahmi O.; Nguyen, Khai V.; Oner, Cihan; Mohammad, A. Mannan; Mandal, Krishna C.
Semi-insulating Cd0.9Zn0.1Te nuclear detector grade crystals were grown by a low temperature solution method from in-house zone refined (~7N) precursor materials. The processed crystals from the grown ingot were thoroughly characterized by using a non-destructive electron beam induced current (EBIC) contrast imaging method. The EBIC results were correlated with the infrared (IR) transmittance mapping, which confirms the variation of contrasts in EBIC is due to non-uniform distribution of tellurium inclusions in the grown CZT crystal. Electrical characteristics of defect regions in the fabricated detectors were further investigated by I-V measurements, and thermally stimulated current (TSC) measurements. Finally, to demonstrate the high quality of the grown CZT crystals, pulse height spectra (PHS) measurements were carried out using gamma radiation sources of 241Am (59.6 keV) and 137Cs (662 keV).
2015-01-01T00:00:00Z