Deterministic optical polarisation in nitride quantum dots at thermoelectrically cooled temperatures

Abstract

We report the successful realisation of intrinsic optical polarisation control by growth, in solid-state quantum dots in the thermoelectrically cooled temperature regime (≥200 K), using a non-polar InGaN system. With statistically significant experimental data from cryogenic to high temperatures, we show that the average polarisation degree of such a system remains constant at around 0.90, below 100 K, and decreases very slowly at higher temperatures until reaching 0.77 at 200 K, with an unchanged polarisation axis determined by the material crystallography. A combination of Fermi-Dirac statistics and k·p theory with consideration of quantum dot anisotropy allows us to elucidate the origin of the robust, almost temperature-insensitive polarisation properties of this system from a fundamental perspective, producing results in very good agreement with the experimental findings. This work demonstrates that optical polarisation control can be achieved in solid-state quantum dots at thermoelectrically cooled temperatures, thereby opening the possibility of polarisation-based quantum dot applications in on-chip conditions.

Insight into the impact of atomic- and nano-scale indium distributions on the optical properties of InGaN/GaN quantum well structures grown on m-plane freestanding GaN substrates

“…Therefore, carrier localization effects due to random alloy fluctuations are not accounted for here. As we have shown before, using atomistic tight-binding calculations, carrier localization effects due to random alloy fluctuations can lead to a high DOLP value over an energy range much wider than the typical valence sub-band splitting expected in a standard 1D continuum-based description of an InGaN QW system 44 . A similar effect will contribute to the temperature dependence of the DOLP.…”

“…pi,j| 2 , which also contains the light polarisation vector a. With increasing temperature T, excited electron and hole states are populated and this effect has been accounted for by Fermi-functions for electrons and holes, which are denoted by f e and f h , respectively 44 . Since indium rich clustered regions have been modelled as QD-like structures, a QD-like description of the spontaneous emission rate has been used in the calculations.…”

Nitride single photon sources

“…While there are ongoing research efforts to fabricate non-polar nitride QDs more deterministically, in terms of both spatial formation control (e.g. site-controlled QDs) and optical properties, it is at this stage important to investigate the QDs' optical properties with statistical significance to understand their underlying photophysics with more useful insights, as several reports [85,[92][93][94] have done. Unlike typical arsenide systems [16], the temperature sensitivity of non-polar nitrides is relatively lower owing to their larger bandgap and stronger exciton binding energies.…”

“…(Cubic GaN in particular suffers from a high density of stacking faults, which could be a candidate carrier trap). For non-polar a-plane InGaN QDs, the linewidth of QDs in most reports are in the range of 0.3 to 3 meV, with 1 meV being both the mean and median [87,89,[91][92][93][94][100][101][102][103]. Although no reports of linewidth < 300 µeV have been made yet, the statistics in Figure 9d suggest that the best current data are limited by the spectral resolution of the relevant experiment, not the fundamental properties of the QDs themselves.…”

Indium gallium nitride quantum dots: Consequence of random alloy fluctuations for polarization entangled photon emission

“…Non-classical light emission via single-photon emission above 200 K has already been demonstrated in the literature for III-N dots. [20,21,22] However, compared to InGaAs/GaAs QDs, entangled photon emission from III-N has been studied far less and if so mainly for GaN/AlN dots, thus for emission in the UV spectral region. [23] When using InGaN/GaN dots, the additional benefit of an in principle flexible emission wavelength engineering in the visible spectral range is possible, while ideally keeping all other benefits (C 3v symmetry, large band offsets, large excitonic binding energies).…”