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Papers by Y. Gurkan Celebi

Physical Review B, 2009

Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In 2 O 3 and SnO 2 . ... more Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In 2 O 3 and SnO 2 . The paramagnetic charge state is stable below ϳ50 K in In 2 O 3 and ϳ30 K in SnO 2 which, coupled with its extremely small effective hyperfine splitting in both cases, allows its identification as the shallow-donor state. This has important implications for the controversial issue of the origins of conductivity in transparent conducting oxides.

Iop Conference Series: Materials Science and Engineering, 2010

Pure indium metal was thermally evaporated in the presence of oxygen atmosphere, with partial pre... more Pure indium metal was thermally evaporated in the presence of oxygen atmosphere, with partial pressure of 6.6×10-2 Pa, onto glass substrates and onto C-Cu grid at room temperature. The structural characteristics of these optically transparent and electrically conducting thin films were investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques and the results are discussed on the base of the differences in their morphologies and thicknesses. Cubic In2O3 and tetragonal In phases, with crystal structures and lattice parameters as reported in the literature, have been identified in the thinnest film having 100 nm thickness. The tendency for amorphization of the cubic and tetragonal phases becomes evident as the film thickness increases.

Materials Research Bulletin, 2005

TlSbSe2 samples used for electrical measurements were cleaved from larger crystals grown by using... more TlSbSe2 samples used for electrical measurements were cleaved from larger crystals grown by using the Bridgman–Stockbarger method. Electrical properties of TlSbSe2 have been carried out as a function of temperature (203–258K) at different dc electric fields. The dc studies revealed the non-ohmic type of conduction (logI versus logV plot). The field lowering coefficientβ is evaluated from logI versus E1/2 plot.

Physical Review B, 2008

Title: Influence of photoexcitation on the diamagnetic muonium states in Ge studied via their pre... more Title: Influence of photoexcitation on the diamagnetic muonium states in Ge studied via their precession signatures. Authors: Fan, I.; Chow, KH; Hitti, B.; Scheuermann, R.; Mansour, AI; Macfarlane, WA; Schultz, BE; Egilmez, M.; Jung, J.; Celebi, YG; Bani-Salameh, HN; Carroll, BR ...

Physica B-condensed Matter, 2007

The muonium analog of hydrogen as an isolated impurity was investigated to above 1000K in n-type,... more The muonium analog of hydrogen as an isolated impurity was investigated to above 1000K in n-type, p-type, and high-resistivity 6H-SiC. Temperature-dependent muon spin precession amplitudes from the combined Mu+ and Mu- states reveal a series of charge-state transitions. The low-temperature transitions in doped samples are assigned to carrier capture processes. Ionization energies in high-resistivity 6H-SiC locate the Mu donor and

Physical Review B, 2009

Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In2O3 and SnO2 . The ... more Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In2O3 and SnO2 . The paramagnetic charge state is stable below ˜50K in In2O3 and ˜30K in SnO2 which, coupled with its extremely small effective hyperfine splitting in both cases, allows its identification as the shallow-donor state. This has important implications for the controversial issue of the origins of conductivity in transparent conducting oxides.

Physica B-condensed Matter, 2009

Preliminary low-field data on the diamagnetic muon spin rotation signal in 4H-SiC are presented. ... more Preliminary low-field data on the diamagnetic muon spin rotation signal in 4H-SiC are presented. The initial results on all three electrical types of 4H-SiC are compared with those for the 6H polytype. Analysis of amplitude transitions at low temperatures in n- and p-type samples indicates carrier capture. At temperatures above 600 K, an increase in diamagnetic amplitude and an associated dip in the phase indicate a slowly formed state in the p-type material. We discuss possible identification of transitions evident from temperature dependent diamagnetic amplitudes and correlations with neutral muonium centers.

Physica B-condensed Matter, 2007

The muonium analog of hydrogen as an isolated impurity was investigated to above 1000 K in n-type... more The muonium analog of hydrogen as an isolated impurity was investigated to above 1000 K in n-type, p-type, and high-resistivity 6H-SiC. Temperature-dependent muon spin precession amplitudes from the combined Mu+ and Mu- states reveal a series of charge-state transitions. The low-temperature transitions in doped samples are assigned to carrier capture processes. Ionization energies in high-resistivity 6H-SiC locate the Mu donor and acceptor levels at EC-280 and EV+860 meV, respectively. The present results place the Mu(+/-) pinning energy in 6H-SiC in excellent agreement with that obtained for other group-IV materials.

Physica B-condensed Matter, 2009

Preliminary low-field data on the diamagnetic muon spin rotation signal in 4H-SiC is presented. T... more Preliminary low-field data on the diamagnetic muon spin rotation signal in 4H-SiC is presented. The initial results on all three electrical types of 4H-SiC are compared with those for the 6H polytype. Analysis of amplitude transitions at low temperatures in n-and p-type samples indicate carrier capture. At temperatures above 600 K, an increase in diamagnetic amplitude and an associated dip in the phase indicate a slowly formed state in the p-type material. We discuss possible identification of transitions evident from temperature dependent diamagnetic amplitudes and correlations with neutral muonium centers.

Journal of Physics-condensed Matter, 2009

The charge state of muonium has been investigated in p-type doped, nominally undoped (low n-type)... more The charge state of muonium has been investigated in p-type doped, nominally undoped (low n-type) and heavily n-type doped InAs. The donor Mu(+) state is shown to be the dominant defect in all cases. Consequently, muonium does not simply counteract the prevailing conductivity in this material. This is consistent with the charge neutrality level lying above the conduction band minimum in InAs.

Muon spin relaxation measurements in the III-V nitrides have provided data on the motion of each ... more Muon spin relaxation measurements in the III-V nitrides have provided data on the motion of each of the three charge-states of the muonium `isotope' of hydrogen. Motional parameters are established for Mu+ in InN, Mu0 in AlN, and Mu- in GaN, with qualitative results in the other materials. Both Mu+ and Mu0 show tunneling below 300 K and thermal diffusion at higher temperatures leading to interactions with other impurities or extended defects.

ABSTRACT Am Inst Phys, in press (2005)

We have recently initiated a study of the defect states formed when positive muons are implanted ... more We have recently initiated a study of the defect states formed when positive muons are implanted into chalcopyrite structured II-IV-V2 compounds to extend our investigation of the muonium defect centers as an experimentally accessible analog of isolated hydrogen defect states in semiconductors. In this presentation, I will discuss one of the initial observations of neutral muonium defect centers in ZnGeP2; specifically, the hyperfine characterization of the neutral muonium centers observed in ZnGeP2 using the Muon Spin Relaxation technique (MuSR). The spin precession frequencies in a field of 4.0 Tesla yield a zero-temperature hyperfine constant of ˜1962 MHz for the promptly formed Mu^0 state. Subsequently, we performed T1-1 longitudinal depolarization measurements in low magnetic fields. Decoupling curves show a different anisotropic Mu^0 with A2=3185 MHz and D=374 MHz, where the D is the dipolar contribution. I will report on the spectroscopic hyperfine characterization of the neutral muonium centers observed in ZnGeP2.

Physical Review B, 2009

Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In 2 O 3 and SnO 2 . ... more Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In 2 O 3 and SnO 2 . The paramagnetic charge state is stable below ϳ50 K in In 2 O 3 and ϳ30 K in SnO 2 which, coupled with its extremely small effective hyperfine splitting in both cases, allows its identification as the shallow-donor state. This has important implications for the controversial issue of the origins of conductivity in transparent conducting oxides.

Iop Conference Series: Materials Science and Engineering, 2010

Pure indium metal was thermally evaporated in the presence of oxygen atmosphere, with partial pre... more Pure indium metal was thermally evaporated in the presence of oxygen atmosphere, with partial pressure of 6.6×10-2 Pa, onto glass substrates and onto C-Cu grid at room temperature. The structural characteristics of these optically transparent and electrically conducting thin films were investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques and the results are discussed on the base of the differences in their morphologies and thicknesses. Cubic In2O3 and tetragonal In phases, with crystal structures and lattice parameters as reported in the literature, have been identified in the thinnest film having 100 nm thickness. The tendency for amorphization of the cubic and tetragonal phases becomes evident as the film thickness increases.

Materials Research Bulletin, 2005

TlSbSe2 samples used for electrical measurements were cleaved from larger crystals grown by using... more TlSbSe2 samples used for electrical measurements were cleaved from larger crystals grown by using the Bridgman–Stockbarger method. Electrical properties of TlSbSe2 have been carried out as a function of temperature (203–258K) at different dc electric fields. The dc studies revealed the non-ohmic type of conduction (logI versus logV plot). The field lowering coefficientβ is evaluated from logI versus E1/2 plot.

Physical Review B, 2008

Title: Influence of photoexcitation on the diamagnetic muonium states in Ge studied via their pre... more Title: Influence of photoexcitation on the diamagnetic muonium states in Ge studied via their precession signatures. Authors: Fan, I.; Chow, KH; Hitti, B.; Scheuermann, R.; Mansour, AI; Macfarlane, WA; Schultz, BE; Egilmez, M.; Jung, J.; Celebi, YG; Bani-Salameh, HN; Carroll, BR ...

Physica B-condensed Matter, 2007

The muonium analog of hydrogen as an isolated impurity was investigated to above 1000K in n-type,... more The muonium analog of hydrogen as an isolated impurity was investigated to above 1000K in n-type, p-type, and high-resistivity 6H-SiC. Temperature-dependent muon spin precession amplitudes from the combined Mu+ and Mu- states reveal a series of charge-state transitions. The low-temperature transitions in doped samples are assigned to carrier capture processes. Ionization energies in high-resistivity 6H-SiC locate the Mu donor and

Physical Review B, 2009

Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In2O3 and SnO2 . The ... more Muonium, and by analogy hydrogen, is shown to form a shallow-donor state in In2O3 and SnO2 . The paramagnetic charge state is stable below ˜50K in In2O3 and ˜30K in SnO2 which, coupled with its extremely small effective hyperfine splitting in both cases, allows its identification as the shallow-donor state. This has important implications for the controversial issue of the origins of conductivity in transparent conducting oxides.

Physica B-condensed Matter, 2009

Preliminary low-field data on the diamagnetic muon spin rotation signal in 4H-SiC are presented. ... more Preliminary low-field data on the diamagnetic muon spin rotation signal in 4H-SiC are presented. The initial results on all three electrical types of 4H-SiC are compared with those for the 6H polytype. Analysis of amplitude transitions at low temperatures in n- and p-type samples indicates carrier capture. At temperatures above 600 K, an increase in diamagnetic amplitude and an associated dip in the phase indicate a slowly formed state in the p-type material. We discuss possible identification of transitions evident from temperature dependent diamagnetic amplitudes and correlations with neutral muonium centers.

Physica B-condensed Matter, 2007

The muonium analog of hydrogen as an isolated impurity was investigated to above 1000 K in n-type... more The muonium analog of hydrogen as an isolated impurity was investigated to above 1000 K in n-type, p-type, and high-resistivity 6H-SiC. Temperature-dependent muon spin precession amplitudes from the combined Mu+ and Mu- states reveal a series of charge-state transitions. The low-temperature transitions in doped samples are assigned to carrier capture processes. Ionization energies in high-resistivity 6H-SiC locate the Mu donor and acceptor levels at EC-280 and EV+860 meV, respectively. The present results place the Mu(+/-) pinning energy in 6H-SiC in excellent agreement with that obtained for other group-IV materials.

Physica B-condensed Matter, 2009

Preliminary low-field data on the diamagnetic muon spin rotation signal in 4H-SiC is presented. T... more Preliminary low-field data on the diamagnetic muon spin rotation signal in 4H-SiC is presented. The initial results on all three electrical types of 4H-SiC are compared with those for the 6H polytype. Analysis of amplitude transitions at low temperatures in n-and p-type samples indicate carrier capture. At temperatures above 600 K, an increase in diamagnetic amplitude and an associated dip in the phase indicate a slowly formed state in the p-type material. We discuss possible identification of transitions evident from temperature dependent diamagnetic amplitudes and correlations with neutral muonium centers.

Journal of Physics-condensed Matter, 2009

The charge state of muonium has been investigated in p-type doped, nominally undoped (low n-type)... more The charge state of muonium has been investigated in p-type doped, nominally undoped (low n-type) and heavily n-type doped InAs. The donor Mu(+) state is shown to be the dominant defect in all cases. Consequently, muonium does not simply counteract the prevailing conductivity in this material. This is consistent with the charge neutrality level lying above the conduction band minimum in InAs.

Muon spin relaxation measurements in the III-V nitrides have provided data on the motion of each ... more Muon spin relaxation measurements in the III-V nitrides have provided data on the motion of each of the three charge-states of the muonium `isotope' of hydrogen. Motional parameters are established for Mu+ in InN, Mu0 in AlN, and Mu- in GaN, with qualitative results in the other materials. Both Mu+ and Mu0 show tunneling below 300 K and thermal diffusion at higher temperatures leading to interactions with other impurities or extended defects.

ABSTRACT Am Inst Phys, in press (2005)

We have recently initiated a study of the defect states formed when positive muons are implanted ... more We have recently initiated a study of the defect states formed when positive muons are implanted into chalcopyrite structured II-IV-V2 compounds to extend our investigation of the muonium defect centers as an experimentally accessible analog of isolated hydrogen defect states in semiconductors. In this presentation, I will discuss one of the initial observations of neutral muonium defect centers in ZnGeP2; specifically, the hyperfine characterization of the neutral muonium centers observed in ZnGeP2 using the Muon Spin Relaxation technique (MuSR). The spin precession frequencies in a field of 4.0 Tesla yield a zero-temperature hyperfine constant of ˜1962 MHz for the promptly formed Mu^0 state. Subsequently, we performed T1-1 longitudinal depolarization measurements in low magnetic fields. Decoupling curves show a different anisotropic Mu^0 with A2=3185 MHz and D=374 MHz, where the D is the dipolar contribution. I will report on the spectroscopic hyperfine characterization of the neutral muonium centers observed in ZnGeP2.