Monolithic multichannel ultraviolet detector arrays and continuous phase evolution in MgxZn1−xO composition spreads

Takeuchi, Ichiro; Yang, Wei; Chang, Kunok; Aronova, Maria A.; Venkatesan, T.; Vispute, R. D.; Bendersky, Leonid A.

doi:10.1063/1.1623923

Cited by 205 publications

(114 citation statements)

References 18 publications

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“…In this work, we have concentrated on alloying ZnO by adding Mg and Cd, which allows for variation of the band gap from high in the ultra-violet (UV) down to the green-yellow visible part in the spectrum, respectively. The band gap of Zn 1−x Mg x O can be tuned in the range between 3.4 eV and 7.8 eV (MgO) [19]. Theoretical studies reveal that the increase of the band gap is mostly due to Mg 3s-like states, which shift the CB states to higher values.…”

Section: Band Gap Engineeringmentioning

confidence: 99%

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Deep level related photoluminescence in ZnMgO

Trunk

Venkatachalapathy

Galeckas

et al. 2010

Applied Physics Letters

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Zinc oxide (ZnO) has been used in a wide range of products for many years, including, among others, varistors, surface acoustic wave devices and cosmetics. Besides these established applications, ZnO and its ternary alloys are now also being considered as potential materials for optoelectronic applications, such as light emitting diodes, photovoltaics, sensors, displays, etc. Unlike other materials, which could be used alternatively, ZnO has the advantage of being inexpensive, chemically stable and relatively plentiful. In spite of the long research history, fabrication of defect free ternary alloys and stable p-type ZnO is still challenging. The aim of this work was therefore to provide a better understanding of ZnO ternary alloys, so that -based on the gained knowledge -their optical properties can be further improved and, in a second step, optoelectronic applications based on these materials can soon be commercialized. The work carried out in this thesis was two-fold: the first part aimed at identifying the origin of defect related luminescence phenomena in ZnMgO, and the second part was dedicated to the exploration of a novel ZnCdO-based heterostructure photovoltaic applications.In the case of ZnMgO, luminescence properties of deep level defects were studied by photoluminescence (PL) spectroscopy and a model was proposed to explain the changes in the deep band emission with increasing Mg content. In this model, the observed trends can be understood by considering interaction of native zinc and oxygen defects of the ZnO sublattice with Mg interstitials (Mg i ). In summary, the deep level bands at 3.0 and 2.8 eV, which show a blueshift with increasing Mg content, were assigned to free-to-bound type transitions between zinc interstitials (Zn i ) with the valence band edge and between the conduction band edge with zinc vacancies (V Zn ), respectively. A red band at 2.0 eV, which does not show an apparent shift of the peak energy for increasing Mg content, is associated with the oxygen vacancies (V O ). Two luminescence bands at 2.3 and 2.5 eV, which are redshifted for higher Mg concentrations, were assigned to transitions between zinc and oxygen interstitials and between zinc interstitials and zinc vacancies, respectively. The redshift is interpreted in terms of a competing supply of electrons from slightly deeper Mg i donor states. The ZnMgO band gap diagram, which the model is based on, has contributed to gain valuable information about the nature of the deep defects both in ZnO and ZnMgO and is therefore of fundamental interest.In the second part of this work, focused on ZnCdO, a stacked heterostructure was designed for iii iv Abstract application in a photoelectrochemical cell, which is used for hydrogen production by photoelectrolysis using the semiconductor as an absorber. Optical and photoelectrochemical measurements led to the conclusion that the optical emission band for the ZnCdO heterostructures is broadened compared to a ZnO single layer. The broadened emission could be explained by combined ...

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Section: Band Gap Engineeringmentioning

confidence: 99%

“…For x > 0.6, the alloy crystallizes in rs structure with the band gap changing according to E g (x) = (3.02 + 4.03x) eV [21]. Between x = 0.4 and 0.6, the band gap is not well defined since phase separation occurs [19].…”

Section: Band Gap Engineeringmentioning

confidence: 99%

Deep level related photoluminescence in ZnMgO

Trunk

Venkatachalapathy

Galeckas

et al. 2010

Applied Physics Letters

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“…[1][2][3][4][5] Machine learning techniques provide a means to convert the large volume of diverse, complex data collected from materials experiments into actionable knowledge refs 6-18 and have been successfully demonstrated in composition spread experiments. Of particular interest is the use of machine learning techniques to rapidly determine potential composition-phase maps from X-ray diffraction (XRD) data from composition spreads.…”

Section: Introductionmentioning

confidence: 99%

Comparison of dissimilarity measures for cluster analysis of X-ray diffraction data from combinatorial libraries

2017

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Machine learning techniques have proven invaluable to manage the ever growing volume of materials research data produced as developments continue in high-throughput materials simulation, fabrication, and characterization. In particular, machine learning techniques have been demonstrated for their utility in rapidly and automatically identifying potential composition-phase maps from structural data characterization of composition spread libraries, enabling rapid materials fabrication-structure-property analysis and functional materials discovery. A key issue in development of an automated phase-diagram determination method is the choice of dissimilarity measure, or kernel function. The desired measure reduces the impact of confounding structural data issues on analysis performance. The issues include peak height changes and peak shifting due to lattice constant change as a function of composition. In this work, we investigate the choice of dissimilarity measure in X-ray diffraction-based structure analysis and the choice of measure's performance impact on automatic composition-phase map determination. Nine dissimilarity measures are investigated for their impact in analyzing X-ray diffraction patterns for a Fe-Co-Ni ternary alloy composition spread. The cosine, Pearson correlation coefficient, and Jensen-Shannon divergence measures are shown to provide the best performance in the presence of peak height change and peak shifting (due to lattice constant change) when the magnitude of peak shifting is unknown. With prior knowledge of the maximum peak shifting, dynamic time warping in a normalized constrained mode provides the best performance. This work also serves to demonstrate a strategy for rapid analysis of a large number of X-ray diffraction patterns in general beyond data from combinatorial libraries.

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“…5 ' 8 Actually, the in situ work of Takeuchi et al on graded MgZnO films has evidenced the appearance of phase separation for 0.4 < x < 0.6 in the form of Mg-rich precipitated nanograins. 9 The large miscibility gap found between MgO and ZnO under thermal equilibrium limits the máximum Mg contení achievable by chemical deposition techniques, but it can be partially overeóme by using molecular beam epitaxy (MBE), since the growth by MBE can be set far from the alloy equilibrium conditions, the elemental fluxes can be controlled independently, and the oxidation efficieney can be enhanced. 1 In fact, the highest reported Mg contents in Mg^Zn^^O (x ~ 0.5) have been obtained using MBE.…”

Section: Introductionmentioning

confidence: 99%

Single phase a-plane MgZnO epilayers for UV optoelectronics: substitutional behaviour of Mg at large contents

et al. 2012

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High quality 1 \im thick a-plane Mg^Zn^^O layers were produced by molecular beam epitaxy with Mg contents higher than 50%. Resonant Rutherford backscattering spectrometry combined with ion channeling revealed a uniform growth in both composition and atomic order. The lattice-site location of Mg, Zn and O elements was determined independently, proving the substitutional behavior of Mg in Zn-sites of the wurtzite lattice. X-Ray diffraction pole figure analysis also confirms the absence of phase separation. Optical properties at such high Mg contents were studied in Schottky photodiodes.

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Monolithic multichannel ultraviolet detector arrays and continuous phase evolution in MgxZn1−xO composition spreads

Cited by 205 publications

References 18 publications

Deep level related photoluminescence in ZnMgO

Deep level related photoluminescence in ZnMgO

Comparison of dissimilarity measures for cluster analysis of X-ray diffraction data from combinatorial libraries

Single phase a-plane MgZnO epilayers for UV optoelectronics: substitutional behaviour of Mg at large contents

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