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- 검색키워드
- 저자 : S.O. Kasap (검색결과 3 건)
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O. Kelekci,P. Tasli,S.S. Cetin,M. Kasap,S. Ozcelik,E. Ozbay 한국물리학회 2012 Current Applied Physics Vol.12 No.6
We investigate the structural and electrical properties of AlxIn1-xN/AlN/GaN heterostructures with AlGaN buffers grown by MOCVD, which can be used as an alternative to AlInN HEMT structures with GaN buffer. The effects of the GaN channel thickness and the addition of a content graded AlGaN layer to the structural and electrical characteristics were studied through variable temperature Hall effect measurements, high resolution XRD, and AFM measurements. Enhancement in electron mobility was observed in two of the suggested AlxIn1-xN/AlN/GaN/Al0.04Ga0.96N heterostructures when compared to the standard AlxIn1exN/AlN/GaN heterostructure. This improvement was attributed to better electron confinement in the channel due to electric field arising from piezoelectric polarization charge at the Al0.04Ga0.96N/GaN heterointerface and by the conduction band discontinuity formed at the same interface. If the growth conditions and design parameters of the AlxIn1-xN HEMT structures with AlGaN buffers can be modified further, the electron spillover from the GaN channel can be significantly limited and even higher electron mobilities, which result in lower two-dimensional sheet resistances, would be possible. We investigate the structural and electrical properties of AlxIn1-xN/AlN/GaN heterostructures with AlGaN buffers grown by MOCVD, which can be used as an alternative to AlInN HEMT structures with GaN buffer. The effects of the GaN channel thickness and the addition of a content graded AlGaN layer to the structural and electrical characteristics were studied through variable temperature Hall effect measurements, high resolution XRD, and AFM measurements. Enhancement in electron mobility was observed in two of the suggested AlxIn1-xN/AlN/GaN/Al0.04Ga0.96N heterostructures when compared to the standard AlxIn1exN/AlN/GaN heterostructure. This improvement was attributed to better electron confinement in the channel due to electric field arising from piezoelectric polarization charge at the Al0.04Ga0.96N/GaN heterointerface and by the conduction band discontinuity formed at the same interface. If the growth conditions and design parameters of the AlxIn1-xN HEMT structures with AlGaN buffers can be modified further, the electron spillover from the GaN channel can be significantly limited and even higher electron mobilities, which result in lower two-dimensional sheet resistances, would be possible.
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Recent advances in X-ray photoconductors for direct conversion X-ray image detectors
S.O. Kasap,M. Zahangir Kabir,J.A. Rowlands 한국물리학회 2006 Current Applied Physics Vol.6 No.3
Recent research on at panel X-ray image detectors has shown their potential for replacing existing X-ray lm/screen cassettes andcapturing X-ray images electronically, thus enabling the clinical transition to digital radiography. The present work examines the imagingproperties of a number of potential X-ray photoconductors for these new X-ray image detectors. The X-ray sensitivity is discussed interms of the absorption eciency, electronhole pair creation energy (ionization energy), and charge transport and trapping limitedattention to stabilized a-Se and HgI2, currently the most promising materials
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Sensitivity of stabilized a-Se based X-ray photoconductors
M. Zahangir Kabir,M. Yunus,S.O. Kasap,O. Tousignant,H. Mani,P. Gauthier 한국물리학회 2006 Current Applied Physics Vol.6 No.3
A model explaining the ghosting mechanisms in amorphous selenium based X-ray image detectors is described by considering deeptrapping of charge carriers, trapped charges arising from previous exposures, trap lling eects, recombination between drifting andtrapped carriers, generation of X-ray induced new deep trap centers, space charge eects, carrier detrapping, and electric eld dependenttions, and the Poisson’s equation across the photoconductor for a pulse X-ray exposure by the nite dierence method. The numericalresults are compared with Monte Carlo simulations. The relative sensitivity decreases with increasing accumulative X-ray exposure anddecreasing applied electric eld. The sensitivity reduction at negative bias is greater than at positive bias. The theoretical model is tted toexperimental data. The comparison of the model with the experimental data reveals that the recombination between trapped and theoppositely charged drifting carriers, electric eld dependent charge carrier generation and X-ray induced new deep trap centers are mainly responsible for the sensitivity reduction in biased amorphous selenium based X-ray detectors.
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