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Mishra J.K.,Indian Institute of Technology Bombay | Dhar S.,Indian Institute of Technology Bombay | Brandt O.,Paul-Drude-Institut fur Festkorperelektronik
Solid State Communications | Year: 2010

Using X-ray diffraction, photoconductivity and temperature dependent conductivity measurements, we investigate GaN:Gd layers grown by reactive molecular-beam epitaxy with the Gd concentration ranging from 7×10 15 to 8.5×10 18 cm -3. Our study reveals that the incorporation of Gd produces a large concentration of defects in the GaN lattice. The density of these defects generated even with a Gd concentration as low as 7×10 15 cm -3 is estimated to be as high as ≈10 19 cm -3. The defect state is found to be located ≈450 meV away from the band edge. © 2010 Elsevier Ltd. All rights reserved. Source


Reshchikov M.A.,Virginia Commonwealth University | Demchenko D.O.,Virginia Commonwealth University | McNamara J.D.,Virginia Commonwealth University | Fernandez-Garrido S.,Paul-Drude-Institut fur Festkorperelektronik | Calarco R.,Paul-Drude-Institut fur Festkorperelektronik
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

A majority of the point defects in GaN that are responsible for broad photoluminescence (PL) bands remain unidentified. One of them is the green luminescence band (GL2) having a maximum at 2.35 eV which was observed previously in undoped GaN grown by molecular-beam epitaxy in Ga-rich conditions. The same PL band was observed in Mg-doped GaN, also grown in very Ga-rich conditions. The unique properties of the GL2 band allowed us to reliably identify it in different samples. The best candidate for the defect which causes the GL2 band is a nitrogen vacancy (VN). We propose that transitions of electrons from the conduction band to the +/2+ transition level of the VN defect are responsible for the GL2 band in high-resistivity undoped and Mg-doped GaN. © 2014 American Physical Society. Source


Reshchikov M.A.,Virginia Commonwealth University | McNamara J.D.,Virginia Commonwealth University | Fernandez-Garrido S.,Paul-Drude-Institut fur Festkorperelektronik | Calarco R.,Paul-Drude-Institut fur Festkorperelektronik
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We have studied the thermal quenching of the ultraviolet luminescence band with a maximum at about 3.25 eV in p-type Mg-doped GaN. The characteristic temperature of the thermal quenching of photoluminescence (PL) gradually shifted to higher temperatures with increasing excitation intensity. This effect is explained by a population inversion of charge carriers at low temperatures, which suddenly converts into a quasiequilibrium population as the temperature increases above the characteristic value. Tunable quenching of PL has been observed only in some of the GaN:Mg samples. The absence of the tunable quenching of PL in another group of GaN:Mg samples is preliminarily attributed to different types of dominant nonradiative defects in the two groups of samples. © 2013 American Physical Society. Source


Puttisong Y.,Linkoping University | Wang X.J.,Linkoping University | Wang X.J.,CAS Shanghai Institute of Technical Physics | Buyanova I.A.,Linkoping University | And 5 more authors.
Nature Communications | Year: 2013

Nuclear spin hyperpolarization is essential to future solid-state quantum computation using nuclear spin qubits and in highly sensitive magnetic resonance imaging. Though efficient dynamic nuclear polarization in semiconductors has been demonstrated at low temperatures for decades, its realization at room temperature is largely lacking. Here we demonstrate that a combined effect of efficient spin-dependent recombination and hyperfine coupling can facilitate strong dynamic nuclear polarization of a defect atom in a semiconductor at room temperature. We provide direct evidence that a sizeable nuclear field (∼150 Gauss) and nuclear spin polarization (∼15%) sensed by conduction electrons in GaNAs originates from dynamic nuclear polarization of a Ga interstitial defect. We further show that the dynamic nuclear polarization process is remarkably fast and is completed in <5 μs at room temperature. The proposed new concept could pave a way to overcome a major obstacle in achieving strong dynamic nuclear polarization at room temperature, desirable for practical device applications. © 2013 Macmillan Publishers Limited. All rights reserved. Source


Puttisong Y.,Linkoping University | Buyanova I.A.,Linkoping University | Ptak A.J.,National Renewable Energy Laboratory | Tu C.W.,University of California at San Diego | And 3 more authors.
Advanced Materials | Year: 2013

The first experimental demonstration of a spin amplifier at room temperature is presented. An efficient, defect-enabled spin amplifier based on a non-magnetic semiconductor, Ga(In)NAs, is proposed and demonstrated, with a large spin gain (up to 2700% at zero field) for conduction electrons and a high cut-off frequency of up to 1 GHz. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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