Spin diffusion in bulk GaN measured with MnAs spin injector

Spin injection and precession in bulk wurtzite $n$-GaN with different doping densities are demonstrated with a ferromagnetic MnAs contact using the three-terminal Hanle measurement technique. Theoretical analysis using minimum fitting parameters indicates that the spin accumulation is primarily in the $n$-GaN channel rather than at the ferromagnet (FM)/semiconductor (SC) interface states. Spin relaxation in GaN is interpreted in terms of the D’yakonov-Perel mechanism, yielding a maximum spin lifetime of 44 ps and a spin diffusion length of 175 nm at room temperature. Our results indicate that epitaxial ferromagnetic MnAs is a suitable high-temperature spin injector for GaN.

Figure 1

(a) Schematic illustration of the device heterostructure and three-terminal Hanle measurement scheme. Inset shows the in-plane hysteresis characteristics of MnAs grown on GaN. (b) Typical $I$-$V$ characteristics of the tunneling FM/SC contact. (c) Zero-bias resistance as a function of temperature for samples A, B, and C, indicating tunneling nature of the FM contact.

Figure 2

Hanle precession characteristics for spin (a) injection and (b) extraction as a function of temperature. (b) Lorentzian fit to experimental data of sample A at 300K. (c) Spin lifetimes at $T$ $=$ 300 K for samples A, B, and C, derived from analysis of measured data.

Figure 3

Spin diffusion length as a function of temperature for samples A, B, and C. Solid lines are guides to the eye.

Figure 4

Expected spin lifetime values within the EY spin-relaxation framework. Inset shows the momentum scattering time (τ${}_p$) as a function of temperature for samples A, B, and C.

Figure 5

Estimated value of relaxation time within the DP framework for each sample with free-fitting parameters. Experimental values are also plotted along with their error ranges.

Figure 6

Estimated value of relaxation time within the DP framework. The Rashba and cubic Dresselhaus parameter values used are α $=$ 0.25 meV nm and β${}_3$ $=$ 0.25 meV nm${}^3$, respectively. Resulting effective Fermi temperatures are 24, 160, and 600 K for samples A, B and C, respectively. Experimental values are also plotted along with their error ranges.