Strain-Induced Effects on the Resonant Tunnelling of Holes in Zinc-Blende Al y Ga 1-y N/Al x Ga 1-x N/Al y Ga 1-y N Hete
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E3.13.1
Strain-Induced Effects on the Resonant Tunnelling of Holes in Zinc-Blende AlyGa1-yN/AlxGa1-xN/AlyGa1-yN Heterostructures C. MEGUENNI, K. ZITOUNI , N. MOKDAD, A. KADRI* Laboratoire d’Etude des Matériaux, Optoélectronique & Polymères (L.E.M.O.P.) Department of Physics, University of Oran (Es-Senia), Oran 31100, Algeria
ABSTRACT We present a multi-band effective mass kP study of built-in strain induced effects on the resonant tunnelling of holes in Zinc-Blende AlyGa1-yN/AlxGa1-xN/AlyGa1-yN Double Barrier Resonant Tunnelling Heterostructures with 0 ≤ x ≤ 0.15 and 0.2 ≤ y ≤ 0.3. We show the influence of the SH split-off band on the resonant tunnelling of light (LH) and heavy (HH) holes through the strain-induced mixing of valence subband states. This valence subbands coupling is shown to result in a broadening of the resonance peaks in SL, LS hole transmission curves and a smearing out of the corresponding resonance peaks in the tunnel current. This effect is shown to decrease with increasing biaxial compression (decreasing x) and is minimum at x=0 in an Al.20Ga.80N/GaN/Al.20Ga.80N heterostructure. INTRODUCTION AlGaN based III-N multi-layered heterostructures have recently attracted considerable attention due to their prospects in various device applications [1] including high frequency resonant tunnelling diodes [2]. In this work, we present a theoretical study of the effects of built-in strain due to the lattice mismatch on the mixing of resonant holes, on their tunnelling transmission and on their tunnelling current in Zinc-Blende AlyGa1-yN/ AlxGa1-xN/ AlyGa1-yN Double Barrier Resonant Tunnelling Heterostructures (DBRTH) as a function of Al contents in the well (x varying from 0 to 0.15) and Al contents in the barriers (y varying from 0.2 to 0.3), for various geometry parameters: barrier (LB) and well (LZ) width values. The cubic structure is preferred here due to the absence of built-in polarization electric field with respect to the hexagonal structure. Our present work was also motivated by the very interesting situation arising at the top of the valence band of GaN/AlGaN quantum wells, where it has been shown [3] that, owing to the very small spin-orbit splitting ∆SO ≈ 20meV, a strong coupling takes place between spin-orbit split-off (SH) subband states, on one hand, and light (LH) and heavy (HH) hole subbands states, on the other hand. Our calculations are performed within a multiband effective mass approach [4], where anisotropy and mixing of the valence subbands states are taken into account through a (6x6) Luttinger-Kohn Hamiltonian[5] including the interactions between light hole (LH), heavy hole (HH), and spin orbite (SH) split-off subbands. The elastic strain effects are included through the Pikus-Bir elastic strain Hamiltonian [6], and the resonant tunneling of holes is described by the transfer matrix technique[7]. In the whole compositions x and y ranges, the quantum well is always under biaxial compression with complicated and simultaneous nonparabolicity and strain-induced mixing effects cont
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