Wavelength tunable InAs/InP quantum dots for photonic devices (Invited)

Wavelength tunable InAs quantum dots (QDs) embedded in a lattice-matched InGaAsP matrix on InP (100) substrates are grown by metalorganic vapor-phase epitaxy (MOVPE). As/P exchange plays an important role in determining QD size and emission wavelength. The As/P exchange reaction is suppressed by decreasing the QD growth temperature and the V/III flow ratio, reducing the QD size and emission wavelength. The As/P exchange reaction and QD emission wavelength are then reproducibly controlled by the thickness of an ultra-thin (0 - 2 monolayers (MLs)) GaAs interlayer underneath the QDs. Submonolayer GaAs coverages result in a shape transition from QD to quantum dash at low V/III flow ratio. Only the combination of reduced growth temperature and V/III flow ratio with the insertion of GaAs interlayers above one ML thickness allows wavelength tuning of QDs at room temperature over the 1.55 µm region. Temperature dependent photoluminescence measurements reveal excellent optical properties of the QDs. © 2005 JSA

InAs/InP self-assembled quantum dots: wavelength tuning and optical nonlinearities

Quantum dots (QDs, i.e., semiconductor nanocrystals) can be formed by spontaneous self-assembly during epitaxial growth of lattice-mismatched semiconductor systems. InAs QDs embedded in GaInAsP on InP are introduced, which can be continuously wavelength-tuned over the 1.55 mm region by inserting ultrathin GaAs or GaP interlayers below them. We subsequently introduce a state-filling optical nonlinearity, which only requires two electron-hole pairs per QD. We employ this nonlinearity for all-optical switching using a Mach-Zehnder interferometric switch. We find a switching energy as low as 6 fJ. [on SciFinder (R)

Strain-driven alignment of in nanocrystals on InGaAs quantum dot arrays and coupled plasmon-quantum dot emission

We report the alignment of In nanocrystals on top of linear InGaAs quantum dot (QD) arrays formed by self-organized anisotropic strain engineering on GaAs (100) by molecular beam epitaxy. The alignment is independent of a thin GaAs cap layer on the QDs revealing its origin is due to local strain recognition. This enables nanometer-scale precise lateral and vertical site registration between the QDs and the In nanocrystals and arrays in a single self-organizing formation process. The plasmon resonance of the In nanocrystals overlaps with the high-energy side of the QD emission leading to clear modification of the QD emission spectrum

Self-aligned epitaxial metal-semiconductor hybrid nanostructures for plasmonics

We demonstrate self-alignment of epitaxial Ag nanocrystals on top of low-density near-surface InAs quantum dots (QDs) grown by molecular beam epitaxy. The Ag nanocrystals support a surface plasmon resonance that can be tuned to the emission wavelength of the QDs. Photoluminescence measurements of such hybrid metal-semiconductor nanostructures reveal large enhancement of the emission intensity. Our concept of epitaxial self-alignment enables the integration of plasmonic functionality with electronic and photonic semiconductor devices operating down to the single QD level

Complex laterally ordered InGaAs and InAs quantum dots by guided self-organized anisotropic strain engineering on artificially patterned GaAs (3 1 1)B substrates

Self-organized anisotropic strain engineering is combined with growth on artificially patterned GaAs (3 1 1)B substrates to realize complex lateral ordering of InGaAs and InAs quantum dots (QDs) guided by steps and facets generated along the pattern sidewalls. Depending on the pattern design, size, and depth (shallow or deep) the natural spotlike arrangement of the QD arrays and groups is transformed into distinct stripes of multiple and single QDs which are ordered over macroscopic areas. Micro-photoluminescence reveals clear influence of the QD ordering on the optical properties. Distinct emission lines are observed from uncapped single QDs

Extended electron states in lateral quantum dot molecules investigated with photoluminescence

InAs quantum dot molecules (QDMs) formed by molecular-beam epitaxy on GaAs (311)B substrates through self-organized anisotropic strain engineering are studied by excitation-power-density- and temperature-dependent macro- and microphotoluminescence (PL). An unusual asymmetric broadening, together with a continuous shift toward higher energies of the PL peak position, most prominent for the p-type modulation-doped QDMs, is observed with increasing excitation power density. The n-type modulation-doped QDMs exhibit a square-shaped PL spectrum, resembling that of modulation-doped quantum wells. In temperature-dependent macro-PL, two distinct minima of the full width at half maximum are observed, indicating thermally activated carrier redistribution within the QDMs through two different channels at lower and higher temperatures. The micro-PL spectra of the p-type modulation-doped QDMs exhibit discrete sets of sharp peaks on top of broad PL bands. The number and intensity of the sharp peaks increase with excitation power density. With increasing temperature, the number and intensity of the sharp peaks decrease while the intensity of the broad PL bands increases, in agreement with the carrier redistribution at lower temperatures. Only broad PL bands are observed for the n-type modulation-doped QDMs with similar behavior. These results are explained by state filling in the presence of extended electron states formed due to lateral electronic coupling of the quantum dots within the QDMs

Self-organized ordered quantum dot molecules (Invited)

No abstract

Shape transition of coherent three-dimensional (In, Ga)As islands on GaAs(100)

The shape transition of coherent three-dimensional (3D) islands is observed experimentally in the (In,Ga)As/GaAs(100) material system. In the molecular-beam epitaxy of a 1.8-nm-thick In0.35Ga0.65As single layer, we find that the shape of the coherent 3D islands transforms from round to elongated when increasing the growth temperature. A quantitative agreement of our experimental data with the theoretical work of Tersoff and Tromp is achieved. ©2001 American Institute of Physics