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Nestor A. Bojarczuk

Bio: Nestor A. Bojarczuk is an academic researcher from IBM. The author has contributed to research in topics: Layer (electronics) & Silicon. The author has an hindex of 35, co-authored 92 publications receiving 5464 citations.


Papers
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Journal ArticleDOI
Byungha Shin1, Oki Gunawan1, Yu Zhu1, Nestor A. Bojarczuk1, S. Jay Chey1, Supratik Guha1 
TL;DR: In this paper, a vacuum process was used to construct a pure sulfide Cu2ZnSnS4 solar cell with 8.4% efficiency, a number independently certified by an external, accredited laboratory.
Abstract: Using vacuum process, we fabricated Cu2ZnSnS4 solar cells with 8.4% efficiency, a number independently certified by an external, accredited laboratory. This is the highest efficiency reported for pure sulfide Cu2ZnSnS4 prepared by any method. Consistent with literature, the optimal composition is Cu-poor and Zn-rich despite the precipitation of secondary phases (e.g., ZnS). Despite a very thin absorber thickness (~600 nm), a reasonably good short-circuit current was obtained. Time-resolved photoluminescence measurements suggest a minority carrier-diffusion length on the order of several hundreds of nanometers and relatively good collection of photo-carriers across the entire absorber thickness. Copyright © 2011 John Wiley & Sons, Ltd.

1,083 citations

Journal ArticleDOI
TL;DR: In this paper, high efficiency solar cells with up to 6.8% efficiency were obtained with absorber layer thicknesses less than 1μm and annealing times in the minutes.
Abstract: High efficiency Cu2ZnSnS4 solar cells have been fabricated on glass substrates by thermal evaporation of Cu, Zn, Sn, and S. Solar cells with up to 6.8% efficiency were obtained with absorber layer thicknesses less than 1 μm and annealing times in the minutes. Detailed electrical analysis of the devices indicate that the performance of the devices is limited by high series resistance, a “double diode” behavior of the current voltage characteristics, and an open circuit voltage that is limited by a carrier recombination process with an activation energy below the band gap of the material.

588 citations

Journal ArticleDOI
TL;DR: In this paper, the authors showed that the control of an interfacial MoSe2 layer thickness and the introduction of an adequate Se partial pressure (PSe) during annealing are essential to achieve high efficiency CZTSe solar cells.
Abstract: We have examined Cu2ZnSnSe4 (CZTSe) solar cells prepared by thermal co-evaporation on Mo-coated glass substrates followed by post-deposition annealing under Se ambient. We show that the control of an interfacial MoSe2 layer thickness and the introduction of an adequate Se partial pressure (PSe) during annealing are essential to achieve high efficiency CZTSe solar cells—a reverse correlation between device performance and MoSe2 thickness is observed, and insufficient PSe leads to the formation of defects within the bandgap as revealed by photoluminescence measurements. Using a TiN diffusion barrier, we demonstrate 8.9% efficiency CZTSe devices with a long lifetime of photo-generated carriers.

308 citations

Journal ArticleDOI
TL;DR: In this paper, the fabrication and characterization of GaN-based double heterostructure light emitting diodes grown by molecular beam epitaxy on Si(111) substrates is reported.
Abstract: We report the fabrication and characterization of GaN-based double heterostructure light emitting diodes grown by molecular beam epitaxy on Si(111) substrates. Light emitting diode operation is achieved by using the conducting Si(111) substrate as a backside n contact and a standard transparent Ni/Au p contact. We observe electroluminescence peaked in the ultraviolet ∼360 nm, with a full width at half maximum of ∼17 nm and in the violet at ∼420 nm. Electron microscopy studies indicate a high density of threading and planar defects. Consequences of these are discussed.

303 citations

Journal ArticleDOI
TL;DR: In this paper, the electrical and microstructural characteristics of La and Y-based oxides grown on silicon substrates by ultrahigh vacuum atomic beam deposition were examined in order to examine their potential as alternate gate dielectrics for Si complementary metal oxide semiconductor technology.
Abstract: We report on the electrical and microstructural characteristics of La- and Y-based oxides grown on silicon substrates by ultrahigh vacuum atomic beam deposition, in order to examine their potential as alternate gate dielectrics for Si complementary metal oxide semiconductor technology. We have examined the issues of polycrystallinity and interfacial silicon oxide formation in these films and their effect on the leakage currents and the ability to deposit films with low electrical thickness. We observe that polycrystallinity in the films does not result in unacceptably high leakage currents. We show significant Si penetration in both types of films. We find that the interfacial SiO2 is much thicker at ∼1.5 nm for the Y-based oxide compared to the La-based oxide where the thickness is <0.5 nm. We also show that while the Y-based oxide films show excellent electrical properties, the La based films exhibit a large flat band voltage shift indicative of positive charge in the films.

288 citations


Cited by
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TL;DR: In this paper, a review of the literature in the area of alternate gate dielectrics is given, based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success.
Abstract: Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...

5,711 citations

01 Sep 1955
TL;DR: In this paper, the authors restrict their attention to the ferrites and a few other closely related materials, which are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present.
Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

2,659 citations

Journal ArticleDOI
TL;DR: In this article, a review of the development of high-k gate oxides such as hafnium oxide (HFO) and high-K oxides is presented, with the focus on the work function control in metal gate electrodes.
Abstract: The scaling of complementary metal oxide semiconductor transistors has led to the silicon dioxide layer, used as a gate dielectric, being so thin (14?nm) that its leakage current is too large It is necessary to replace the SiO2 with a physically thicker layer of oxides of higher dielectric constant (?) or 'high K' gate oxides such as hafnium oxide and hafnium silicate These oxides had not been extensively studied like SiO2, and they were found to have inferior properties compared with SiO2, such as a tendency to crystallize and a high density of electronic defects Intensive research was needed to develop these oxides as high quality electronic materials This review covers both scientific and technological issues?the choice of oxides, their deposition, their structural and metallurgical behaviour, atomic diffusion, interface structure and reactions, their electronic structure, bonding, band offsets, electronic defects, charge trapping and conduction mechanisms, mobility degradation and flat band voltage shifts The oxygen vacancy is the dominant electron trap It is turning out that the oxides must be implemented in conjunction with metal gate electrodes, the development of which is further behind Issues about work function control in metal gate electrodes are discussed

1,520 citations

Patent
01 Aug 2008
TL;DR: In this article, the oxide semiconductor film has at least a crystallized region in a channel region, which is defined as a region of interest (ROI) for a semiconductor device.
Abstract: An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

1,501 citations

Journal ArticleDOI
TL;DR: In this article, the choice of oxides, their structural and metallurgical behaviour, atomic diffusion, their deposition, interface structure and reactions, their electronic structure, bonding, band offsets, mobility degradation, flat band voltage shifts and electronic defects are discussed.
Abstract: The scaling of complementary metal oxide semiconductor (CMOS) transistors has led to the silicon dioxide layer used as a gate dielectric becoming so thin (1.4 nm) that its leakage current is too large. It is necessary to replace the SiO2 with a physically thicker layer of oxides of higher dielectric constant (κ) or 'high K' gate oxides such as hafnium oxide and hafnium silicate. Little was known about such oxides, and it was soon found that in many respects they have inferior electronic properties to SiO2 ,s uch as a tendency to crystallise and a high concentration of electronic defects. Intensive research is underway to develop these oxides into new high quality electronic materials. This review covers the choice of oxides, their structural and metallurgical behaviour, atomic diffusion, their deposition, interface structure and reactions, their electronic structure, bonding, band offsets, mobility degradation, flat band voltage shifts and electronic defects. The use of high K oxides in capacitors of dynamic random access memories is also covered.

1,500 citations