Spin-orbit coupling is investigated by magnetoconductivity measurements in wurtzite AlxGa1-xN/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
×1012 cm-2 to 10.6 ×1012 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 kF as 2( ακF + γκF3) with effective linear and cubic spin-orbit parameters of
-α= 5.01×10−13 eV • m and γ= 1.6 ×10−31 eV •m3, 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 spinorbit
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.
We study AlxGa1-xN/AlN/GaN heterostructures with a two-dimensional-electron-gas (2DEG) grown on different GaN
templates using low-temperature magneto-transport measurements. Heterostructures with different Al compositions are
grown by metal-organic vapor phase epitaxy (MOVPE) on three different templates; conventional undoped GaN (u-
GaN), epitaxial lateral overgrown GaN (ELO-GaN), and in situ ELO-GaN using a SixNy nanomask layer (SiN-GaN).
Field-dependent magneto-resistance and Hall measurements indicated that in addition to 2DEG, the overgrown
heterostructures had a parallel conducting layer. The contact resistance for the parallel channels was large so that it
introduced errors in the quantitative mobility spectrum analysis (QMSA) of the data. Notwithstanding complexities
introduced by parallel conducting channels in mobility analysis in SiN-GaN and ELO-GaN samples, we were able to
observe Shubnikov-de Haas (SdH) oscillations in all samples, which confirmed the existence of 2DEGs. To characterize
the parallel channel, we repeated the transport measurements after the removal of the 2DEG by etching the
heterostructure. The 2DEG carrier density values were extracted from the SdH data, whereas the zero-field 2DEG
conductivity was determined by subtracting the parallel channel conductivity from the total conductivity. The resulting
2DEG mobility was significantly higher (about a factor of 2) in the ELO-GaN and SiN-GaN samples as compared to the
standard control sample. The mobility enhancement is attributed to the threading dislocation reduction by both ELO
techniques.
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