Photoreflectance study of hydrogenated (InGa)(AsN)/GaAs heterostructures
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M8.31.1
Photoreflectance study of hydrogenated (InGa)(AsN)/GaAs heterostructures M. Geddo1, G. Guizzetti2, R. Pezzuto2, A. Polimeni3, M. Capizzi3, M. Bissiri3 , G. Baldassarri Höger von Högersthal,3 D. Gollub4 and A. Forchel4 1 INFM-UdR Pavia, Via Bassi 6, I-27100 Pavia and Dipartimento di Fisica dell'Università di Parma, Viale delle Scienze 7a, I-43100 Parma, Italy 2 INFM-Dip. di Fisica “A. Volta”, Università di Pavia, Via Bassi 6, I-27100 Pavia, Italy 3 INFM-Dip. di Fisica, Università degli Studi di Roma “La Sapienza”, Piazzale A. Moro 2, I00185 Roma, Italy 4 Universität Würzburg, Technische Physik, Am Hubland 97074 Würzburg, Germany
ABSTRACT We report on photoreflectance measurements performed in the 0.8-1.6 eV photon energy range in as grown and hydrogenated InxGa1-xAs1-yNy/GaAs single quantum wells grown on GaAs substrates by molecular beam epitaxy. In the hydrogenated samples, a blueshift of all the QW spectral features and a surprising change with temperature in the nature of the lowest energy transition are found. These features are related to the interaction of H with N atoms. An increase in the binding energy of the heavy-hole exciton upon N introduction into the InxGa1-xAs lattice has been measured also and explained in terms of an increase in the electron effective mass. INTRODUCTION Since their first proposal, (InGa)(AsN)/GaAs heterostructures have attracted much interest as GaAs-compatible emitters in the 1.3-1.55 µm wavelength range. Nitrogen incorporation in (InGa)As leads to large changes in the energy value and in the hydrostatic pressure and temperature dependence of the band gap of the host material.[1] These effects have been accounted for in terms of a hydrogen induced perturbation of the highly localized potential introduced by N in the host lattice.[2-3] Recently, photoluminescence results[4] have shown that the optical properties of the (InGa)(AsN) system are strongly affected by hydrogen irradiation, which reduces the effective concentration of N atoms and reopens the material band gap. In this paper, different QW interband transitions are observed in as-grown and hydrogenated (InGa)(AsN) heterostructures by exploiting the phase-sensitive detection and the derivative-like nature of the photoreflectance (PR) technique. The PR spectra are analyzed according to a line shape model characteristic of modulation spectroscopy in confined systems.[5] The experimental results are interpreted using current models describing the highly localized character of the perturbation introduced by the nitrogen atoms in the (InGa)As lattice. They are compared then with the predictions of recent calculations concerning the band structure of III-N-V alloys[6] and the increase of the exciton binding energy in the perturbed host lattice.[7] EXPERIMENTAL The heterostructures investigated here were grown on GaAs substrates by solid source molecular beam epitaxy. They consist of a 500 nm thick GaAs buffer, a 6 nm thick single
M8.31.2
InxGa1-xAs1-yNy well, and a 100 nm thick GaAs cap layer. N2 cracking was obtained
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