Gate-controlled spin splitting in GaN∕AlN quantum wells

Abstract

A new mechanism (∆ C1 -∆ C3 coupling) is accounted for the spin splitting of wurtzite GaN, which is originated from the intrinsic wurtzite effects (band folding and structure inversion asymmetry). The band-folding effect generates two conduction bands (∆ C1 and ∆ C3 ), in which p-wave probability has tremendous change when k z approaches anti-crossing zone. The spin-splitting energy induced by the ∆ C1 -∆ C3 coupling and wurtzite structure inversion asymmetry is much larger than that evaluated by traditional Rashba or Dresselhaus effects. When we apply the coupling to GaN/AlN quantum wells, we find that the spin-splitting energy is sensitively controllable by an electric field. Based on the mechanism, we proposed a p-wave-enhanced spin-polarized field effect transistor, made of In x Ga 1-x N/In y Al 1-y N, for spintronics application. _____________________ Keywords: GaN, Spintronics, Spin-field effect transistor, Rashba effect, Dresselhaus effect. PACS numbers: 71.15.Ap, 72.25.Dc, 73.21.Fg 2 I. IntroductionGate-controlled spin splitting in two dimensional electron system has been investigated in many zinc-blende III-V semiconductor quantum wells. 1,2 The gate-controlled spin splitting is arisen from the spin-orbit coupling 3 in zinc-blende structure with respect to inversion asymmetry.Carriers confined in asymmetric quantum wells will experience an effective magnetic field that may induce spin precession. 4 The manipulation of electron spins in a semiconductor is one of the key problems in the field of spintronics, in which additional degrees of freedom executed by electron spins are expected to play important roles in future nano-scaled electronic devices. 5,6 The spin splitting in zinc-blende III-V compound is induced either by a bulk inversion asymmetry of crystal potential (the k 3 -term, called Dresselhaus effect), 7 or by a structure inversion asymmetry of electrostatic confinement potential (the linear-k term, named Rashba effect). 8 Ganichev et al. have demonstrated the spin-orbital Hamiltonian of Rashba or Dresselhaus effects for zinc-blende InAs quantum well (QW) in terms of a k-dependent effective crystal magnetic field B eff (k); e.g., H SO = σ‧B eff (k), where k is the electron wave vector and σ the vector of Pauli matrices. The presence of B eff (k) implies that the spin orientation of electrons depends on the k-dependent Rashba and Dresselhaus terms. 4 Recently, Tsubaki et al. 9 and our group 10 independently observed a large spin-splitting energy (greater than 5 meV) in the 2DEG of GaN/AlGaN wurtzite heterostructures. The wurtzite GaN-based QW can be a potential candidate to realize the gate-controlled spin-polarized devices. However, the spin-splitting energy of wurtzite GaN, calculated by a traditional Rashba model (~1 meV), is much smaller than the measured values. 11,12 Reviewing the spin-orbital interaction in wurtzite semiconductors, Lew Yan Voon et al. have pointed out that, in addition to Dresselhaus k 3 -term, there exists a linear-k term spin-splitting energy caused by an intrinsic struc...

Prediction of extremely long mobile electron spin lifetimes at room temperature in wurtzite semiconductor quantum wells

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