Persistent template effect in InAs/GaAs quantum dot bilayers

Abstract

The dependence of the optical properties of InAs/GaAs quantum dot ͑QD͒ bilayers on seed layer growth temperature and second layer InAs coverage is investigated. As the seed layer growth temperature is increased, a low density of large QDs is obtained. This results in a concomitant increase in dot size in the second layer, which extends their emission wavelength, reaching a saturation value of around 1400 nm at room temperature for GaAs-capped bilayers. Capping the second dot layer with InGaAs results in a further extension of the emission wavelength, to 1515 nm at room temperature with a narrow linewidth of 22 meV. Addition of more InAs to high density bilayers does not result in a significant extension of emission wavelength as most additional material migrates to coalesced InAs islands but, in contrast to single layers, a substantial population of regular QDs remains.

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

“…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.…”

“…Past experimental studies have shown that the size of the QDs increases with the stacking number 12,25,26 in multilayer QD stacks. Thus, the aspect ratio AR of the QDs in upper layers may increase above 0.3.…”

“…Thus, the aspect ratio AR of the QDs in upper layers may increase above 0.3. 2,25 In such QD systems, the first few conduction band and valence band states will be confined in the upper layers (larger QDs). This is because the stronger strain interaction of the larger QDs will push the energy levels of the smaller QDs to higher values.…”

Subthreshold diode characteristics of InAs/GaAs quantum dot lasers

“…The QD bilayers comprise two closely-stacked QD layers, separated by 10 nm GaAs: a seed layer that determines the overall QD density and an upper layer, for which the growth conditions can then be chosen to provide a significant extension in the emission wavelength. The two QD layers are sufficiently close together to allow efficient carrier transfer from the seed layer to the upper layer, such that emission from the seed layer is suppressed and device operation is determined by the upper layer QDs [7,8]. The active region is an undoped 500 nm thick layer of GaAs containing three QD bilayers separated by 50 nm bounded by n and p-doped 1500 nm thick Al 0.33 Ga 0.67 As cladding layers.…”

Tamm plasmons for efficient interaction of telecom wavelength photons and quantum dots

“…It would therefore be particularly valuable to have sources that emit at wavelengths in the telecommunication bands (1.3 or 1.55 μm), as these have notably lower levels of attenuation through optical fibres. It is possible to fabricate QDs in a GaAs spacer layer, either as high-density ensembles for room temperature operation or as single-emitters at low temperature, that emit at 1.3 μm wavelengths [6], [7]. Another challenge is that QDs emit isotropically and are incorporated in high refractive index materials, which makes efficient photon extraction difficult [8].…”