Spin-orbit coupling in AlGaN/AlN/GaN heterostructures with a polarization induced two-dimensional electron gas

摘要

Spin-orbit coupling is investigated by magnetoconductivity measurements in wurtzite Al_xGa_(1-x)N/AlN/GaN heterostructures with a polarization induced two-dimensional electron gas with different Al concentrations ranging from x = 0.1 to 0.35. By employing the persistent photoconductivity effect and by gating we are able to vary the carrier density of the samples in a controllable manner from 0.8 ×10~(12) cm~(-2) to10.6×l0~(12) cm~(-2). The samples are characterized using magnetoresistance measurements. To characterize the spin-orbit interaction we measured quantum corrections to conductance at low magnetic fields. All the samples we studied exhibit a weak antilocalization feature at liquid He temperatures. The zero-field electron spin-splitting energies extracted from the weak antilocalization measurements are found to scale with the Fermi wavevector k_F as 2(αk_F + γk_F~3) with effective linear and cubic spin-orbit parameters of α= 5.01 × 10~(-13) eV·m and γ= 1.6 × 10~(-31) eV·m~3, respectively. The linear spin-orbit coupling arises from both the bulk inversion asymmetry of the crystal and the structural inversion asymmetry of the heterostructure whereas the cubic spin-orbit coupling parameter is purely due to the bulk inversion asymmetry of the wurtzite crystal. We also extracted phase coherence times from the amplitude of the weak antilocalization feature. The measured phase coherence times ranged from 3-40 ps and were in agreement with the theory of decoherence based on electron-electron interactions.