Columbus School for Girls

Columbus, OH, United States

Columbus School for Girls

Columbus, OH, United States
SEARCH FILTERS
Time filter
Source Type

Foster G.M.,Ohio State University | Faber G.,Columbus School for Girls | Yao Y.-F.,National Taiwan University | Yang C.C.,National Taiwan University | And 5 more authors.
Applied Physics Letters | Year: 2016

Due to a strong Fermi-level mismatch, about 10% of the electrons in a 5-nm-thick highly Ga-doped ZnO (GZO) layer grown by molecular beam epitaxy at 250 °C on an undoped ZnO buffer layer transfer to the ZnO (Debye leakage), causing the measured Hall-effect mobility (μH) of the GZO/ZnO combination to remarkably increase from 34 cm2/V s, in thick GZO, to 64 cm2/V s. From previous characterization of the GZO, it is known that ND = [Ga] = 1.04 × 1021 and NA = [VZn] = 1.03 × 1020 cm-3, where ND, NA, and [VZn] are the donor, acceptor, and Zn-vacancy concentrations, respectively. In the ZnO, ND = 3.04 × 1019 and NA = 8.10 × 1018 cm-3. Assuming the interface is abrupt, theory predicts μH = 61 cm2/V s, with no adjustable parameters. The assumption of abruptness in [Ga] and [VZn] profiles is confirmed directly with a differential form of depth-resolved cathodoluminescence spectroscopy coupled with X-ray photoelectron spectroscopy. An anneal in Ar at 500 °C for 10 min somewhat broadens the profiles but causes no appreciable degradation in μH and other electrical properties. © 2016 Author(s).


Foster G.M.,Ohio State University | Perkins J.,Ohio State University | Myer M.,Columbus School for Girls | Mehra S.,Columbus School for Girls | And 6 more authors.
Physica Status Solidi (A) Applications and Materials Science | Year: 2015

With the rise of MgZnO alloys as UV optoelectronic components, deep level defects in these materials have assumed added importance due to their impact on free carrier recombination, heterojunction band offsets, and Schottky barriers. Yet their dependence on alloy content and lattice structure is relatively unexplored. We have used depth-resolved cathodoluminescence spectroscopy and nanoscale surface photovoltage spectroscopy to measure the dependence of native point defect energies and densities on Mg content, band gap, and lattice structure in non-polar, single-phase MgxZn1-xO (0 ≤ x ≤ 0.56) alloys grown by molecular beam epitaxy (MBE) on r-plane sapphire substrates. Based on this wide range of alloy compositions, we identified multiple deep level emissions due to zinc and oxygen vacancies whose densities exhibit a pronounced minimum at ∼45% Mg corresponding to similar a and c parameter minima at ∼52%. This minimum also corresponds to a pronounced change in Schottky barriers reported previously. The reduction in unit cell volume appears to inhibit defect formation due to electrostatic repulsion as reflected in DFT calculations that assess the roles of electric fields and strain on the native defect distribution. These results highlight the coupled electronic and structural changes that occur across this wide alloy series. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA.


Perkins J.,Ohio State University | Foster G.M.,Ohio State University | Myer M.,Columbus School for Girls | Mehra S.,Columbus School for Girls | And 6 more authors.
APL Materials | Year: 2015

We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the densities, energy levels, and spatial distributions of zinc/magnesium cation and oxygen vacancies in isostructural, single-phase, non-polar MgxZn1-xO alloys over a wide (0 ≤ x ≤ 0.56) range. Within this wide range, both defect types exhibit strong Mg content-dependent surface segregation and pronounced bulk density minima corresponding to unit cell volume minima, which can inhibit defect formation due to electrostatic repulsion. Mg in ZnO significantly reduces native defect densities and their non-polar surface segregation, both major factors in carrier transport and doping of these oxide semiconductors. © 2015 Author(s).

Loading Columbus School for Girls collaborators
Loading Columbus School for Girls collaborators