In-plane polarization anisotropy of ground state optical intensity in InAs/GaAs quantum dots

Abstract

The design of optical devices such as lasers and semiconductor optical amplifiers for telecommunication applications requires polarization insensitive optical emissions in the region of 1500 nm. Recent experimental measurements of the optical properties of stacked quantum dots have demonstrated that this can be achieved via exploitation of inter-dot strain interactions. In particular, the relatively large aspect ratio (AR) of quantum dots in the optically active layers of such stacks provide a two-fold advantage, both by inducing a red shift of the gap wavelength above 1300 nm, and increasing the TM001-mode, thereby decreasing the anisotropy of the polarization response. However, in large aspect ratio quantum dots (AR > 0.25), the hole confinement is significantly modified compared with that in lower AR dots-this modified confinement is manifest in the interfacial confinement of holes in the system. Since the contributions to the ground state optical intensity (GSOI) are dominated by lower-lying valence states, we therefore propose that the room temperature GSOI be a cumulative sum of optical transitions from multiple valence states. This then extends previous theoretical studies of flat (low AR) quantum dots, in which contributions arising only from the highest valence state or optical transitions between individual valence states were considered. The interfacial hole distributions also increases in-plane anisotropy in tall (high AR) quantum dots (TE110 not equal TE-110), an effect that has not been previously observed in flat quantum dots. Thus, a directional degree of polarization (DOP) should be measured (or calculated) to fully characterize the polarization response of quantum dot stacks. Previous theoretical and experimental studies have considered only a single value of DOP: either [110] or [-110]. (C) 2011 American Institute of Physics. [doi:10.1063/1.3657783

Atomistic theoretical study of electronic and polarization properties of single and vertically stacked elliptical InAs quantum dots

“…In remainder of this paper, we label the single QD with AR = 0.225 as a "flat" QD and the single QD with AR = 0.40 as a "tall" QD. In a previous study 10 , it has been shown that the flat and tall QDs with an ideal circularbase exhibit drastically different electronic and polarization properties. The hole wave functions tend to reside in the HH pockets for the tall QDs, when the AR 0.25.…”

“…This paper, therefore, aims to bridge this gap by providing a detailed study of the DOP [ − → n ] and Pol || for the [110]-and [110]-elongated QDs. For the calculation of the polarization dependent optical modes (TE and TM), we take into account the highest five valence band states, instead of just a single top most valence band state, in accordance with the recent studies 5,10 where it has been shown that the calculation of the room temperature ground state optical spectra must involve multiple closely spaced valence band states to accurately model the in-plane polarizability and to avoid discrepancy between the theory and experiments. Our calculations show that despite tuning of the DOP [ − → n ] over a wide range, the elliptical shapes of the single QDs do not lead to an isotropic polarization.…”

Understanding the electric field control of the electronic and optical properties of strongly-coupled multi-layered quantum dot molecules

“…For a single isolated QDL, it is well-known in the literature that the symmetry of the lowest electron state is s-type and it is of p-type for the next (first) two excited states [39].…”

Tuning of polarization sensitivity in closely stacked trilayer InAs/GaAs quantum dots induced by overgrowth dynamics

“…The simulations were performed using well-known NanoElectronic MOdeling (NEMO 3-D) simulator [21,22], in which the strain is computed from atomistic Valence Force Field (VFF) model [23][24][25] and the electronic structure is computed by solving twenty-band sp 3 d 5 s * tight-binding Hamiltonian [26]. The polarization dependent interband optical transition strengths (TE and TM modes) are calculated using Fermi's Golden Rule [3,27].…”