High optical quality, well end leg faceted ZnO microtetrapods with leg length between 1 and 12 µm... more High optical quality, well end leg faceted ZnO microtetrapods with leg length between 1 and 12 µm have been grown by carbothermal chemical vapor deposition. Lasing with mode quality factors of 2500-3000 is demonstrated. The origin of laser resonator cavity is discussed as a function of the tetrapod size. It is shown that in big tetrapods with legs of 12 µm in length the laser emission lines are well explained by longitudinal Fabry-Pérot modes generated in cavities formed by individual tetrapod legs. The dispersion of the ZnO refractive index is experimentally determined from the position of lasing modes in the temperature interval from 10 to 300 K. It is shown that the lasing mode structure is seriously affected by the decrease of the tetrapod size. For a small tetrapod with a leg length of 1 µm, the lasing modes cannot be explained anymore by the formation of longitudinal Fabry-Pérot modes in separate tetrapod legs, and the generation of guided modes by multiple total internal reflections in single tetrapod legs or in pairs of legs should be taken into account. The correlations between the lasing threshold and the tetrapod size are discussed.
Methodologies have been evolved to grow optical quality nanostructures of the 3.4 eV band-gap sem... more Methodologies have been evolved to grow optical quality nanostructures of the 3.4 eV band-gap semiconductor ZnO and its doped variants with different orders of dimensionality. These nanostructures are versatile and yet under evolution for next generation UV-blue photonic and spin-photonic devices. There are pending lacunae such as reliable and enduring p-type carrier doping and large carrier mobility etc, which need
ABSTRACT We report on the synthesis and characterization of vapor phase grown zinc oxide nanorod ... more ABSTRACT We report on the synthesis and characterization of vapor phase grown zinc oxide nanorod arrays on sputtered aluminum-doped zinc oxide substrates. These arrays can serve as nanostructured electrodes for P3HT:PCBM solar cells, possibly improving their photovoltaic performance.
Incorporating tailored nanostructures into solar cells is a promising way to improve their photov... more Incorporating tailored nanostructures into solar cells is a promising way to improve their photovoltaic conversion efficiency. For such solar cells, sputtered indium-doped tin oxide on glass is the standard substrate. As the global resources of indium are very limited, there is the challenge to ...
We investigate the properties of random lasing in nanocrystalline ZnO powders. The lowest thresho... more We investigate the properties of random lasing in nanocrystalline ZnO powders. The lowest threshold for lasing occurs for average particle diameters of about 260 nm. Reproducible lasing features are achieved for reduced ensemble sizes. Spatially resolved luminescence spectroscopy is used to probe directly the degree of localization of random laser mode. We find that strongly confined and extended modes can co-exist in the same spatial area. However, localized modes appear for small optical gain while extended modes are only supported in the presence of large optical gain, as is expected from theory.
The research on ZnO has a long history but experiences an extremely vivid revival during the last... more The research on ZnO has a long history but experiences an extremely vivid revival during the last 10 years. We critically discuss in this didactical review old and new results concentrating on optical properties but presenting shortly also a few aspects of other fields like transport or magnetic properties. We start generally with the properties of bulk samples, proceed then to epitaxial layers and nanorods, which have in many respects properties identical to bulk samples and end in several cases with data on quantum wells or nano crystallites. Since it is a didactical review, we present explicitly misconceptions found frequently in submitted or published papers, with the aim to help young scientists entering this field to improve the quality of their submitted manuscripts. We finish with an appendix on quasi two-and one-dimensional exciton cavity polaritons.
Using indium as catalyst for growth and simultaneously as doping source, ordered arrays of n-type... more Using indium as catalyst for growth and simultaneously as doping source, ordered arrays of n-type ZnO single crystal nanorods have been perpendicularly grown on p-GaN/Al2O3 substrates with a vapor phase transport growth method. The low temperature photoluminescence measurements of the n-ZnO nanorods show dominant In-related neutral donor bound exciton emission in the ultraviolet region. Electrical transport measurements performed on single
The electrical properties of field-effect transistors fabricated on the basis of single ZnO nanor... more The electrical properties of field-effect transistors fabricated on the basis of single ZnO nanorods were analyzed under ambient conditions and in the chamber of a scanning electron microscope under high-vacuum conditions. Under ambient conditions, the threshold voltage and conductivity may depend strongly on the details of the measurement procedure as the chosen gate voltage range and gate voltage sweep direction.
We investigated the photoluminescence properties of ZnO nanowires coated with Au, Ag, and Pt nano... more We investigated the photoluminescence properties of ZnO nanowires coated with Au, Ag, and Pt nanoparticles deposited by dc sputtering. A strong enhancement of the near-band-edge emission was observed in all metal-coated samples but also if the samples were treated with Ar plasma without any nanoparticle deposition. High-resolution photoluminescence spectroscopy revealed hydrogen-donor-bound-exciton emission in all samples indicating unintentional hydrogen incorporation. A shorter decay time of the near-band-edge emission was observed in all cases. The results indicate that unintentional hydrogen incorporation plays a dominant role when metal deposition is performed by sputtering.
High optical quality, well end leg faceted ZnO microtetrapods with leg length between 1 and 12 µm... more High optical quality, well end leg faceted ZnO microtetrapods with leg length between 1 and 12 µm have been grown by carbothermal chemical vapor deposition. Lasing with mode quality factors of 2500-3000 is demonstrated. The origin of laser resonator cavity is discussed as a function of the tetrapod size. It is shown that in big tetrapods with legs of 12 µm in length the laser emission lines are well explained by longitudinal Fabry-Pérot modes generated in cavities formed by individual tetrapod legs. The dispersion of the ZnO refractive index is experimentally determined from the position of lasing modes in the temperature interval from 10 to 300 K. It is shown that the lasing mode structure is seriously affected by the decrease of the tetrapod size. For a small tetrapod with a leg length of 1 µm, the lasing modes cannot be explained anymore by the formation of longitudinal Fabry-Pérot modes in separate tetrapod legs, and the generation of guided modes by multiple total internal reflections in single tetrapod legs or in pairs of legs should be taken into account. The correlations between the lasing threshold and the tetrapod size are discussed.
High optical quality, well end leg faceted ZnO microtetrapods with leg length between 1 and 12 µm... more High optical quality, well end leg faceted ZnO microtetrapods with leg length between 1 and 12 µm have been grown by carbothermal chemical vapor deposition. Lasing with mode quality factors of 2500-3000 is demonstrated. The origin of laser resonator cavity is discussed as a function of the tetrapod size. It is shown that in big tetrapods with legs of 12 µm in length the laser emission lines are well explained by longitudinal Fabry-Pérot modes generated in cavities formed by individual tetrapod legs. The dispersion of the ZnO refractive index is experimentally determined from the position of lasing modes in the temperature interval from 10 to 300 K. It is shown that the lasing mode structure is seriously affected by the decrease of the tetrapod size. For a small tetrapod with a leg length of 1 µm, the lasing modes cannot be explained anymore by the formation of longitudinal Fabry-Pérot modes in separate tetrapod legs, and the generation of guided modes by multiple total internal reflections in single tetrapod legs or in pairs of legs should be taken into account. The correlations between the lasing threshold and the tetrapod size are discussed.
Methodologies have been evolved to grow optical quality nanostructures of the 3.4 eV band-gap sem... more Methodologies have been evolved to grow optical quality nanostructures of the 3.4 eV band-gap semiconductor ZnO and its doped variants with different orders of dimensionality. These nanostructures are versatile and yet under evolution for next generation UV-blue photonic and spin-photonic devices. There are pending lacunae such as reliable and enduring p-type carrier doping and large carrier mobility etc, which need
ABSTRACT We report on the synthesis and characterization of vapor phase grown zinc oxide nanorod ... more ABSTRACT We report on the synthesis and characterization of vapor phase grown zinc oxide nanorod arrays on sputtered aluminum-doped zinc oxide substrates. These arrays can serve as nanostructured electrodes for P3HT:PCBM solar cells, possibly improving their photovoltaic performance.
Incorporating tailored nanostructures into solar cells is a promising way to improve their photov... more Incorporating tailored nanostructures into solar cells is a promising way to improve their photovoltaic conversion efficiency. For such solar cells, sputtered indium-doped tin oxide on glass is the standard substrate. As the global resources of indium are very limited, there is the challenge to ...
We investigate the properties of random lasing in nanocrystalline ZnO powders. The lowest thresho... more We investigate the properties of random lasing in nanocrystalline ZnO powders. The lowest threshold for lasing occurs for average particle diameters of about 260 nm. Reproducible lasing features are achieved for reduced ensemble sizes. Spatially resolved luminescence spectroscopy is used to probe directly the degree of localization of random laser mode. We find that strongly confined and extended modes can co-exist in the same spatial area. However, localized modes appear for small optical gain while extended modes are only supported in the presence of large optical gain, as is expected from theory.
The research on ZnO has a long history but experiences an extremely vivid revival during the last... more The research on ZnO has a long history but experiences an extremely vivid revival during the last 10 years. We critically discuss in this didactical review old and new results concentrating on optical properties but presenting shortly also a few aspects of other fields like transport or magnetic properties. We start generally with the properties of bulk samples, proceed then to epitaxial layers and nanorods, which have in many respects properties identical to bulk samples and end in several cases with data on quantum wells or nano crystallites. Since it is a didactical review, we present explicitly misconceptions found frequently in submitted or published papers, with the aim to help young scientists entering this field to improve the quality of their submitted manuscripts. We finish with an appendix on quasi two-and one-dimensional exciton cavity polaritons.
Using indium as catalyst for growth and simultaneously as doping source, ordered arrays of n-type... more Using indium as catalyst for growth and simultaneously as doping source, ordered arrays of n-type ZnO single crystal nanorods have been perpendicularly grown on p-GaN/Al2O3 substrates with a vapor phase transport growth method. The low temperature photoluminescence measurements of the n-ZnO nanorods show dominant In-related neutral donor bound exciton emission in the ultraviolet region. Electrical transport measurements performed on single
The electrical properties of field-effect transistors fabricated on the basis of single ZnO nanor... more The electrical properties of field-effect transistors fabricated on the basis of single ZnO nanorods were analyzed under ambient conditions and in the chamber of a scanning electron microscope under high-vacuum conditions. Under ambient conditions, the threshold voltage and conductivity may depend strongly on the details of the measurement procedure as the chosen gate voltage range and gate voltage sweep direction.
We investigated the photoluminescence properties of ZnO nanowires coated with Au, Ag, and Pt nano... more We investigated the photoluminescence properties of ZnO nanowires coated with Au, Ag, and Pt nanoparticles deposited by dc sputtering. A strong enhancement of the near-band-edge emission was observed in all metal-coated samples but also if the samples were treated with Ar plasma without any nanoparticle deposition. High-resolution photoluminescence spectroscopy revealed hydrogen-donor-bound-exciton emission in all samples indicating unintentional hydrogen incorporation. A shorter decay time of the near-band-edge emission was observed in all cases. The results indicate that unintentional hydrogen incorporation plays a dominant role when metal deposition is performed by sputtering.
High optical quality, well end leg faceted ZnO microtetrapods with leg length between 1 and 12 µm... more High optical quality, well end leg faceted ZnO microtetrapods with leg length between 1 and 12 µm have been grown by carbothermal chemical vapor deposition. Lasing with mode quality factors of 2500-3000 is demonstrated. The origin of laser resonator cavity is discussed as a function of the tetrapod size. It is shown that in big tetrapods with legs of 12 µm in length the laser emission lines are well explained by longitudinal Fabry-Pérot modes generated in cavities formed by individual tetrapod legs. The dispersion of the ZnO refractive index is experimentally determined from the position of lasing modes in the temperature interval from 10 to 300 K. It is shown that the lasing mode structure is seriously affected by the decrease of the tetrapod size. For a small tetrapod with a leg length of 1 µm, the lasing modes cannot be explained anymore by the formation of longitudinal Fabry-Pérot modes in separate tetrapod legs, and the generation of guided modes by multiple total internal reflections in single tetrapod legs or in pairs of legs should be taken into account. The correlations between the lasing threshold and the tetrapod size are discussed.
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Papers by J. Sartor