Electron emission from multilayer ensembles of vertically coupled InAs quantum dots in an n -GaAs matrix
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DIMENSIONAL SYSTEMS
Electron Emission from Multilayer Ensembles of Vertically Coupled InAs Quantum Dots in an n-GaAs Matrix A. A. Gutkina^, P. N. Brunkova, A. Yu. Egorovb, A. E. Zhukovb, and S. G. Konnikova a
Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia ^e-mail: [email protected] b St. Petersburg Physics and Technology Centre for Research and Education, Russian Academy of Sciences, ul. Khlopina 8, korp. 3, St. Petersburg, 195220 Russia Submitted December 24, 2007; accepted for publication December 29, 2007
Abstract—Electron emission from multilayer arrays of vertically coupled InAs quantum dots into the n-GaAs matrix in Schottky-barrier structures (electron concentration n ≈ 2 × 1016 cm–3) is studied by admittance spectroscopy. It is established that, in the temperature region below ~70 K, electron emission in a rate range of 3 × 104–3 × 106 s–1 proceeds via thermally activated tunneling through intermediate virtual states. As the number of layers in the quantum dot array increases from three to ten, a decrease in the electron emission rate is observed. PACS numbers: 73.21.La, 73.63.Kv DOI: 10.1134/S1063782608090170
Emission of charge carriers captured by quantum dots (QDs) in a semiconductor matrix substantially affects the parameters of electron devices based on such heterostructures [1, 2]. Study of the mechanisms of this emission and determination of its rates and various factors affecting their magnitude are the necessary for improvement of similar devices. An effective method of studying the emission properties and electron states of QDs is varying the temperature dependences of various quasi-steady-state and non-steady-state processes in semiconductor structures with a potential barrier, the region of space charge of which involves the QD array [1–6]. Similar studies were performed for arrays of one [1, 2, 5, 6] and three [4] InAs QD layers in GaAs. However, the effect of the number of the layers on the variation in the emission rates of charge carriers captured by the QD array was not studied in this case. Still, in the multilayer ensembles of vertically coupled QDs, these quantities can noticeably differ from the rates determined for one layer because of the variations in the bonding energy of carriers and occupancy of the QD electron states, which depend on the number of layers in the array [7–10]. The magnitude of the effect of these factors on the emission rate should in turn depend on the emission mechanism. In this study, we examined the emission rates of electrons from the arrays containing three, six, and ten vertically coupled InAs QDs in the n-GaAs epitaxial layers with the electron concentration n ≈ 2 × 1016 cm–3 and the Schottky barrier formed on the surface. The thicknesses and doping of n-GaAs layers were selected so that, at the zero bias voltage, the space charge region of the Schottky barrier did not reach the QD layer,
while with an increase in reverse bias voltage across the structure, the QD array turned out
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