Weak antilocalization in a polarization-doped AlxGa1−xN∕GaN heterostructure with single subband occupation

Abstract

Spin-orbit scattering in a polarization-doped Al 0.30 Ga 0.70 N / GaN two-dimensional electron gas with one occupied subband is studied at low temperatures. At low magnetic fields weak antilocalization is observed, which proves that spin-orbit scattering occurs in the two-dimensional electron gas. From measurements at various temperatures the elastic scattering time tr , the dephasing time , and the spin-orbit scattering time so are extracted. Measurements in tilted magnetic fields were performed, in order to separate spin and orbital effects. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2162871͔ GaN-based layer systems are very interesting candidates regarding the realization of future spin-based electronics ͑spintronics͒. The interest in this material for spintronics was ignited by the theoretical prediction that diluted magnetic semiconductor based on GaN should show Curie temperatures above room temperature. 1 GaN-based diluted magnetic semiconductors are promising materials for spin injection because of their expected good matching to AlGaN / GaN heterostructures. However, for a successful realization of spintronic devices an essential prerequisite is that the spin orientation can be controlled externally. A prominent example is the spin transistor proposed by Datta and Das. 2 Here, the spin orientation in a two-dimensional electron gas ͑2DEG͒ is controlled by a gate electrode via the Rashba spin-orbit coupling originating from a macroscopic electric field in an asymmetric quantum well. 3 For semiconductor quantum wells with a large band gap channel layer, i.e., GaN, it is not obvious that the Rashba effect is suffciently strong, because the Rashba coupling parameter ␣ decreases with increasing band gap. However, recently it was shown theoretically that owing to the polarization field at the AlGaN / GaN heterointerface and owing to the large carrier concentration a relatively large Rashba spinsplitting energy can be expected. 4 Experimentally information on the Rashba effect can be obtained from the characteristic beating pattern in the Shubnikov-de Haas oscillations 5,6 or by analyzing weak antilocalization. 7,8 For some AlGaN / GaN heterostructures a characteristic beating pattern was observed in the magnetoresistance, which was interpreted as the presence of the Rashba effect. [9][10][11][12] In addition to the Rashba effect, the lack of inversion symmetry in zincblende-type or wurtzite-type semiconductors can also alter the spin orientation during the electron propagation ͑Dresselhaus term͒. 13 The question to which extent spin-orbit coupling affects the electron transport in an AlGaN / GaN 2DEG is still not solved completely. One reason is, that the observation of beating effects in the Shubnikov-de Haas oscillations is not an unambiguous signature for the presence of spin-orbit coupling. 11,14 In contrast, we focused on analyzing weak antilocalization at very low magnetic fields in a polarizationdoped AlGaN / GaN heterostructure which is a unambiguous indication of spin-orbit effects. Randomi...

Weak antilocalization and zero-field electron spin splitting inAlxGa1−xN∕AlN∕GaNheterostructures with a polarization-induced two-dimen

“…8 These terms have not been measured independently in the wurtzite system. Moreover, recent experiments based on Shubnikov-de Haas (SdH), 9,10 weak antilocalization (WAL), 11,12,13 and circular photogalvanic 14 measurements have given conflicting results for the spin splitting in wurtzite AlGaN/GaN heterostructures. In particular, spin-splitting energies extracted from the beat pattern of SdH measurements are found to be as large as 9 meV, which is about an order of magnitude larger than the theoretical estimates based on the Rashba coupling mechanism for this material system.…”

“…Qualitatively, these results are consistent with the recent WAL measurements performed on a similar AlGaN/GaN heterostructure with a 2DEG. [11][12][13] However, the size of the WAL feature Thillosen et al…”

“…11 Note that the sizes of quantum interference corrections to conductivity are typically on the order of e 2 /2πh.…”

Spin–orbit interaction and weak localization in heterostructures

“…[14,15,16,17,18]. In the work by Yu et al [18] the structures with an electric gate were investigated with allowance for a change of concentration and mobility of 2D electrons.…”

“…and the operator Q(q) differs by an additional factor iX/R in the integrand (14). L is the operator of spin difference of interfering particles.…”