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ASU Scholarship Showcase


This growing collection consists of scholarly works authored by ASU-affiliated faculty, students and community members, and contains many open access articles. ASU-affiliated authors are encouraged to Share Your Work in the ASU Digital Repository.


Series
  • JOURNAL OF APPLIED PHYSICS
Date Range
2013 2016


InGaN semiconductors are promising candidates for high-efficiency next-generation thin film solar cells. In this work, we study the photovoltaic performance of single-junction and two-junction InGaN solar cells using a semi-analytical model. We analyze the major loss mechanisms in InGaN solar cell including transmission loss, thermalization loss, spatial relaxation loss, and recombination loss. We find that transmission loss plays a major role for InGaN solar cells due to the large bandgaps of III-nitride materials. Among the recombination losses, Shockley-Read-Hall recombination loss is the dominant process. Compared to other III-V photovoltaic materials, we discovered that the emittance of InGaN solar cells is ...

Contributors
Huang, Xuangqi, Fu, Houqiang, Chen, Hong, et al.
Created Date
2016-06-01

The current work explores the crystalline perovskite oxide, strontium hafnate, as a potential high-k gate dielectric for Ge-based transistors. SrHfO3 (SHO) is grown directly on Ge by atomic layer deposition and becomes crystalline with epitaxial registry after post-deposition vacuum annealing at ∼700 °C for 5 min. The 2 × 1 reconstructed, clean Ge (001) surface is a necessary template to achieve crystalline films upon annealing. The SHO films exhibit excellent crystallinity, as shown by x-ray diffraction and transmission electron microscopy. The SHO films have favorable electronic properties for consideration as a high-k gate dielectric on Ge, with satisfactory band offsets ...

Contributors
McDaniel, Martin D., Hu, Chengqing, Lu, Sirong, et al.
Created Date
2015-02-07

The objective of this research is to explore the formation/binding energetics and length scales associated with the interaction between He [subscript n] V clusters and grain boundaries in bcc α-Fe. In this work, we calculated formation/binding energies for 1–8 He atoms in a monovacancy at all potential grain boundary (GB) sites within 15 Å of the ten grain boundaries selected (122106 simulations total). The present results provide detailed information about the interaction energies and length scales of 1–8 He atoms with grain boundaries for the structures examined. A number of interesting new findings emerge from the present study. First, the ...

Contributors
Tschopp, M. A., Gao, F., Solanki, Kiran, et al.
Created Date
2014-06-21

The optical properties of intersubband transition in a semipolar AlGaN/GaN single quantum well (SQW) are theoretically studied, and the results are compared with polar c-plane and nonpolar m-plane structures. The intersubband transition frequency, dipole matrix elements, and absorption spectra are calculated for SQW on different semipolar planes. It is found that SQW on a certain group of semipolar planes (55° < θ < 90° tilted from c-plane) exhibits low transition frequency and long wavelength response with high absorption quantum efficiency, which is attributed to the weak polarization-related effects. Furthermore, these semipolar SQWs show tunable transition frequency and absorption wavelength with ...

Contributors
Fu, Houqiang, Lu, Zhijian, Huang, Xuangqi, et al.
Created Date
2016-05-05

Chemical vapor deposition methods were developed, using stoichiometric reactions of specialty Ge[subscript 3]H[subscript 8] and SnD[subscript 4] hydrides, to fabricate Ge[subscript 1-y]Sn[subscript y] photodiodes with very high Sn concentrations in the 12%–16% range. A unique aspect of this approach is the compatible reactivity of the compounds at ultra-low temperatures, allowing efficient control and systematic tuning of the alloy composition beyond the direct gap threshold. This crucial property allows the formation of thick supersaturated layers with device-quality material properties. Diodes with composition up to 14% Sn were initially produced on Ge-buffered Si(100) featuring previously optimized n-Ge/i-Ge[subscript 1-y]Sn[subscript y]/p-Ge[subscript 1-z]Sn[subscript z] type ...

Contributors
Senaratne, Charutha Lasitha, Wallace, Patrick, Gallagher, John, et al.
Created Date
2016-07-13

Modulated reflectance (contactless electroreflectance (CER), photoreflectance (PR), and piezoreflectance (PzR)) has been applied to study direct optical transitions in bulk MoS[subscript 2], MoSe[subscript 2], WS[subscript 2], and WSe[subscript 2]. In order to interpret optical transitions observed in CER, PR, and PzR spectra, the electronic band structure for the four crystals has been calculated from the first principles within the density functional theory for various points of Brillouin zone including K and H points. It is clearly shown that the electronic band structure at H point of Brillouin zone is very symmetric and similar to the electronic band structure at K ...

Contributors
Kopaczek, J., Polak, M. P., Scharoch, P., et al.
Created Date
2016-06-21

The (110) plane of Co[subscript 3]O[subscript 4] spinel exhibits significantly higher rates of carbon monoxide conversion due to the presence of active Co[superscript 3+] species at the surface. However, experimental studies of Co[subscript 3]O[subscript 4] (110) surfaces and interfaces have been limited by the difficulties in growing high-quality films. We report thin (10–250 Å) Co[subscript 3]O[subscript 4] films grown by molecular beam epitaxy in the polar (110) direction on MgAl[subscript 2]O[subscript 4] substrates. Reflection high-energy electron diffraction, atomic force microscopy, x-ray diffraction, and transmission electron microscopy measurements attest to the high quality of the as-grown films. Furthermore, we investigate the ...

Contributors
Kormondy, Kristy J., Posadas, Agham B., Slepko, Alexander, et al.
Created Date
2014-06-28

Direct bandgap InP, GaAs, CdTe, and Ga0.5In0.5P solar cells containing backside mirrors as well as parasitically absorbing substrates are analyzed for their limiting open circuit voltage and power conversion efficiency with comparison to record solar cells. From the principle of detailed balance, it is shown quantitatively that mirror solar cells have greater voltage and power conversion efficiency than their substrate counterparts. Next, the radiative recombination coefficient and maximum radiative lifetime of GaAs mirror and substrate solar cells are calculated and compared to the nonradiative Auger and Shockley-Read-Hall (SRH) lifetimes. Mirror solar cells have greater radiative lifetime than their substrate variants. ...

Contributors
Kirk, Alexander, Kirk, Wiley P., Ira A. Fulton Schools of Engineering, et al.
Created Date
2013-12-06

Novel hydride chemistries are employed to deposit light-emitting Ge [subscript 1- y] Sn [subscript y] alloys with y ≤ 0.1 by Ultra-High Vacuum Chemical Vapor Deposition (UHV-CVD) on Ge-buffered Si wafers. The properties of the resultant materials are systematically compared with similar alloys grown directly on Si wafers. The fundamental difference between the two systems is a fivefold (and higher) decrease in lattice mismatch between film and virtual substrate, allowing direct integration of bulk-like crystals with planar surfaces and relatively low dislocation densities. For y ≤ 0.06, the CVD precursors used were digermane Ge [subscript 2]H[subscript 6] and deuterated stannane ...

Contributors
Senaratne, Charutha Lasitha, Gallagher, J. D., Jiang, Liying, et al.
Created Date
2014-10-07

In recent years, a substantial amount of research has been focused on identifying suitable interfacial layers in organic light-emitting diodes and organic solar cells which has efficient charge transport properties. In this work, a very thin layer of AgOx is deposited on top of the ITO layer along with PEDOT:PSS and is observed that the solar cells having the AgOx interfacial layer showed a 28% increase in power conversion efficiency in comparison to that of the control cell. The enhancement in efficiency has been ascribed to improvements in fill factor as well as the increase in shunt resistance and decrease ...

Contributors
Das, Sayantan, Alford, Terry, Department of Chemistry and Biochemistry, et al.
Created Date
2014-07-28