Interplay Between Strain and Effective Electron Mass on the Absorption Strength of Dilute Nitride Semiconductor Quantum
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0940-P08-20
Interplay Between Strain and Effective Electron Mass on the Absorption Strength of Dilute Nitride Semiconductor Quantum Wires Andrea Feltrin, Andenet Alemu, and Alexandre Freundlich Center for Advanced Materials, University of Houston, 724 Science & Research Building 1, Houston, Texas, 77204-5004
ABSTRACT We have investigated the absorption spectrum and strength of InyGa1-yAs1-xNx quantum wires. We show that compounds with varying fractions of indium and nitrogen, but similar band gaps have different absorption patterns. This behavior is related to the interplay between different effects as strain, which mainly affects the band offsets, and the increased electron mass in dilute nitride III-V semiconductors. We also study how the influence of these parameters changes with the optical band gaps associated to common optical telecommunication wavelengths. Our model calculations are performed in the parabolic band approximation and include excitonic effects. INTRODUCTION In the past decade III-V semiconductor compounds and alloys with diluted nitrogen content like GaAs1-xNx or InyGa1-yAs1-xNx, have attracted a growing attention because of their unusual electronic properties. The incorporation of small amounts of nitrogen in III-V semiconductor compounds causes an impressive reduction of the optical band gap [1]. This behavior has been explained in terms of the band anticrossing (BAC) model [2]. BAC assumes that the band gap reduction is caused by the interaction between localized nitrogen states and extended conduction band electron states of the host material [3,4]. A further consequence of this interaction is the modification of the electron energy dispersion in the reciprocal space and the increase of the conduction band electron effective mass [5]. Recently, quantum nanostructures with dilute nitrogen content have been demonstrated and their optical properties are currently investigated in quantum wells [6] and quantum dots [7]. The evaluation of the absorption in these structures is of particular importance as it affects directly the performance of devices like optical modulators or detectors. In this work, the effect of In and N compositions on absorption properties of vertical InyGa1yAs1-xNx wires tuned to common optical telecommunication wavelengths (980 nm, 1300 nm and 1550 nm) is investigated. THEORY Confined levels and excitons in quantum wires For our model calculations we consider an ideal quantum wire with a square cross section, the side of the square being L = 12 nm. The choice of a square cross section simplifies our
calculations, but does not limit the validity of our results for wires with other cross sections. Electrons (e), light holes (lh) and heavy holes (hh) are confined in two dimensions and are free to move in the third one (along the QWR axis which we take to be the z axis). We assume that the QWR axis coincides with the crystallographic [001] axis, which can be achieved, for instance, by fabricating an array of vertical QWRs on a (001) oriented substrate. We also assume that th
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