Study of the nonlinear Rashba spin splitting in AlGaN/GaN heterostructures by the perturbative expansion method

By considering the energy dispersion of the conduction subband and using the perturbative expansion method, the dependence of all order contributions to the Rashba coefficient (α) and nonlinear Rashba spin splitting (ΔE) in AlGaN/GaN quantum wells (QWs) on the in-plane wave vector (k//) are studied. The zeroth-order contribution to α only comes from the heterointerface, and does not depend on k//. The first-order correction α(1) contributing from the well (ΓW(1)) and the barrier (ΓB(1)) are not related to k//, but the contribution from the heterointerface (ΓInter(1)) and the higher corrections to α all depend on k//. So the zeroth-order contribution to ΔE and the first-order correction ΔE(1) contributing from the well and barrier increase linearly with k//, while the contribution to ΔE(1) from the heterointerface and the higher corrections to ΔE all increase nonlinearly with k//. Therefore, the linear Rashba model could be assumed as an approximation of the nonlinear Rashba model, and the difference between the two models is relatively minute at small wave vectors, especially for wide-gap semiconductors.