Electronic structure of piezoelectric double-barrier InAs/InP/InAs/InP/InAs (111) nanowires

Abstract

We present a theoretical study of an n-type InAs nanowire with built-in InAs/InP heterojunctions in the effective-mass approximation via self-consistent Poisson–Schrödinger calculations in cylindrical coordinates. Rapid convergence and efficiency are achieved by (i) a suitable transformation of the radial part of the Hamiltonian matrix thereby maintaining symmetry (ii) using quantum mechanical perturbation theory to derive an expression for the change in electron density with electrostatic potential. We calculate the energy levels in a 150 Å long InAs quantum dot surrounded by 50 Å long InP barriers within an InAs quantum wire of radius 200 Å, having a doping level of 3×1016 cm−3 and conduction-band discontinuities of ΔECB=0.6 eV. In equilibrium, the lowest quantum dot state is at 15 meV above the Fermi level and we find that upon variation of the applied collector–emitter voltage VCE, resonance occurs at VCE=88 mV. This is in good agreement with an experimental study of resonant tunneling in a nominally undoped InAs/InP nanowire of similar dimensions grown in the [111] direction, where resonance was detected at VCE=80 mV, and a small shift (<5 mV) in its position occurred upon inverting the voltage polarity. We rule out barrier asymmetry, bandbending due to impurities or defects, and contact effects as being the origin of the resonant-voltage shift, and attribute it to the strain-induced charges at the InP/InAs interfaces. Both InAs and InP segments are shown to be under in-plane compression giving a piezoelectric field of 0.155 meV/Å in the InAs quantum dot while resonant tunneling, as calculated, occurs at 84 mV for VCE<0 and at 87 mV for VCE>0. This is in contrast to two-dimensional pseudomorphic heteroepitaxy, where the InP is under in-plane tensile strain yielding a very strong resonance-voltage shift (≫5 mV). The small magnitude of the measured shift indicates that in nanowires any strain at the heterointerfaces relaxes within a few atomic layers.

Structural and Room‐Temperature Transport Properties of Zinc Blende and Wurtzite InAs Nanowires

“…[24] Therefore, we assumed here a lower bound of 10 13 cm À2 for the spontaneous polarization charge density of InAs, which was introduced at the edges of the WZ/ZB segments of the channel in the following simulations. We note that strain-induced piezoelectric charges in the InAs/InP double barrier NW heterostrcuctures [25] have been used to explain the asymmetry of tunnel resonance peaks with the polarity of applied voltage. [26] In the WZ NWs subjected to these studies, the average lattice spacing of the {0001} planes was 0.3536 nm, deduced from the average of six HRTEM images (Fig.…”

Near-field measurement of spectral anisotropy and optical absorption of isolated ZnO nanorod single-quantum-well structures

“…16,17 The small Stokes shift may result from the decreased piezoelectric polarization effect by the fully relaxed strain for the ZnO / ZnMgO nanorod quantum structures in contrast to the two-dimensional ͑2D͒ ZnO / ZnMgO heteroepitaxial multiple layers are strongly supported by the theoretical calculation on the double barrier lnAs/lnP nanorod heterostructures. 18 Based on these experiments, a major investigation of the optical properties of isolated ZnO SQWs was performed by analyzing the polarization-dependent PL spectrum of isolated ZnO SQWs ͑L w = 3.75 nm͒. As shown in Fig.…”

Nanowires: Promising Candidates for Electrostatic Control in Future Nanoelectronic Devices

“…Quantum threshold voltage obtained using the analytical model is validated in Fig. 11 with numerical simulation data obtained with a cylindrical Schrödinger-Poisson solver (Munteanu & Autran, 2003;Zervos & Feiner, 2004). We can note that the quantum confinement tends to limit SCE.…”