Weak Antilocalization in Polarization-Doped Al x Ga 1-x N/GaN Heterostructures
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0892-FF17-02.1
Weak Antilocalization in Polarization-Doped AlxGa1-xN/GaN Heterostructures N. Thillosen, Th. Schäpers, N. Kaluza, H. Hardtdegen, and V.A. Guzenko Institute of Thin Films and Interfaces (ISG1) and Virtual Institute of Spin Electronics (VISel), Research Center Jülich GmbH, 52425 Jülich, Germany
ABSTRACT Spin-orbit scattering has been studied in a polarization-doped Al0.30Ga0.70N/GaN twodimensional electron gas by measuring weak antilocalization at low magnetic fields and low temperatures. Thereby, the occupancy of a single subband in the well demonstrated that intersubband scattering can not be considered as the origin of spin-orbit scattering in such systems. As a consequence, an alternative explanation by means of Dresselhaus- and Rashbaeffect will be given. Finally, from measurements at various temperatures, elastic scattering time τtr, dephasing time τφ as well as spin-orbit scattering time τso were extracted and related to an effective spin-orbit coupling parameter αeff.
INTRODUCTION The interest in GaN for spin-based electronics (spintronics) has been initiated by the theoretical prediction that diluted magnetic semiconductors based on GaN should exhibit Curie temperatures above room temperature [1]. Using GaN-based diluted magnetic semiconductors as electrodes for spin injection in heterostructures also helps to overcome the problem of conductivity-mismatch [2], with a good matching to AlGaN/GaN heterostructures. A further condition for realizing spintronic devices, as for example the transistor proposed by Datta and Das [3], is that the spin orientation can be controlled externally. In this case, the spin orientation in a two-dimensional electron gas (2DEG) is controlled by a gate voltage via the Rashba spin-orbit coupling originating from a macroscopic electric field in an asymmetric quantum well [4]. The large band gap of GaN was a long time considered as a disadvantage for a strong Rashba effect, as the Rashba coupling parameter α decreases with increasing band gap. Recently, theoretical calculations showed, however, that owing to the large polarization fields at the AlGaN/GaN heterointerface and owing to the large carrier concentration, a non negligible Rashba effect can be expected [5]. Experimentally, from magnetoresistance measurements, the Rashba-effect can be observed and quantified by analyzing either the high-field part of the Shubnikov-de Haas oscillations (characteristic beating pattern due to Rashba spin-splitting [6,7]) or the low-field part by means of weak antilocalization [8,9]. For some AlGaN/GaN heterostructures, beating pattern were already observed in the magnetoresistance and interpreted as the presence of Rashba effect [10-13]. In addition to the tunable spin-orbit coupling by Rashba-effect that is wished for the spin-transistor, a fixed spin-orbit coupling is induced by a crystal-lattice without inversion symmetry, as this is the case for zincblende-type or wurtzite-type semiconductors (Dresselhaus term) [14]. In this case, the spin orientation is altered in a similar
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