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

Abstract

Spin-orbit coupling is studied using the quantum interference corrections to conductance in AlGaN/AlN/GaN two-dimensional electron systems where the carrier density is controlled by the persistent photoconductivity effect. All the samples studied exhibit a weak antilocalization feature with a spin-orbit field of around 1.8 mT. The zero-field electron spin splitting energies extracted from the weak antilocalization measurements are found to scale linearly with the Fermi wavevector ( E SS = 2αk f ) with an effective linear spin-orbit coupling parameter α = 5.5 ×10 −13 eV ⋅ m. The spin-orbit times extracted from our measurements varied from 0.74 to 8.24 ps within the carrier density range of this experiment.PACS Numbers: 71.70.Ej, 73.20.Fz, 73.40 To help resolve these issues, we have performed WAL and SdH measurements on three Al x Ga 1-x N/AlN/GaN samples with different Al concentrations. We used the persistent photoconductivity effect to vary the carrier density of the two-dimensional electron gas (2DEG). 18 The electron spin splitting energies extracted from our weak antilocalization Magnetoresistance and Hall measurements were performed in a variable temperature cryostat with a base temperature of 1.6 K. The samples exhibited SdH oscillations and integer quantum Hall effect at high magnetic fields. As expected, the carrier density of the sample with the highest Al fraction (Sample C) had the highest carrier density. To change the carrier density of the samples, we have illuminated the top surface of the samples through the optical access port of the cryostat via a flashlight. After each illumination the carrier density of the sample increases and does not drop to its equilibrium concentration, unless the sample is warmed up to room temperature. 20 By using the persistent photoconductivity effect we were able to vary the carrier density of 5 the samples in a controllable manner over the ranges of 0.8-1.3 ×10 12 cm -2 , 1.7-4.9 ×10 12 cm -2 , and 3.1-6.7 ×10 12 cm -2 for samples A, B, and C, respectively. Sample B had the highest electron mobility of µ = 20,300 cm 2 /V ⋅ s at a carrier concentration of n = 4.9 ×10 12 cm -2 . Consistent with previous studies based on gated structures, at low carrier densities the electron mobility is found to be decreasing with decreasing carrier density. 21 Typical high field magnetoresistivity traces obtained from these three samples are shown in Fig. 1. From the temperature dependence of SdH oscillations, we extracted an effective electron mass of m * = 0.23m e . We could not resolve any beat feature in the SdH oscillations even at high carrier densities where the onset of SdH is around 2 Tesla.The SdH oscillations also indicate that only a single subband of the quantum well is occupied by the 2DEG. Furthermore, at high carrier densities, we could resolve SdH oscillations corresponding to filling fractions above 100 which implies that the carrier density was uniform throughout our device even after illumination.The absence of any beat feature in the SdH oscillations prevented u...

Zero Field Spin Splitting in GaN/AlGaN Heterostructures Probed by the Weak Antilocalization

“…The zero field spin splitting energy for two studied samples equals to 0.23 and 0.35 meV. These values are comparable with those obtained by other groups for GaN/AlGaN heterostructures [7][8][9][10], but also are close to spin splitting in GaAs based heterostructures, where definitely both, bulk and structure inversion asymmetry are present [11]. The origin of such a large spin splitting in GaN/AlGaN could be revealed when bulk and structure inversion asymmetry contributions could be separated.…”

Spin dynamics in semiconductors

“…Indeed, experiments revealed that the spin-orbit coupling is dominated by the Rashba-type spin-orbit coupling, where no effect that signals spin-orbit coupling of the form of (k x σ x − k y σ y ) was observed [247,[256][257][258][259][260]. The measured Rashba parameter lies in the range of 0.6 to 8 × 10 −12 eV m various conditions [251][252][253][254][261][262][263][264][265][266][267][268].…”

“…10 In contrast to the zincblende semiconductors such as GaAs, the existence of hexagonal c-axis in wurtzite semiconductors leads to an intrinsic wurtzite structure inversion asymmetry in addition to the bulk inversion asymmetry [246,247]. Therefore, the electron spin splittings include both the Dresselhaus effect [245,248] (cubic in k) and Rashba effect (linear in k) [124,125,[249][250][251][252][253][254]. In a recent work by Fu and Wu [245], a Kane-type Hamiltonian was constructed and the spin-orbit coupling for electron and hole bands were investigated in the full Brillouin zone in bulk ZnO and GaN.…”

Enhanced spin-orbit scattering length in narrowAlxGa1−xN∕GaNwires

“…[2][3][4][5][6][7][8][9][10][11] Spin-orbit coupling in Al x Ga 1−x N / GaN two-dimensional electron gases ͑2DEGs͒ can be investigated by analyzing the characteristic beating pattern in Shubnikov-de Haas oscillations, [2][3][4][5] by measuring the circular photogalvanic effect, 6 or by studying weak antilocalization. 4,7,[9][10][11] The latter is an electron interference effect where the random deviations of the spin orientations between time-reversed paths result in an enhanced conductance. [12][13][14] From weak antilocalization measurements, information on characteristic length scales, i.e., the spin-orbit scattering length l so and the phase coherence length l , can be obtained.…”