We present a detailed investigation into the optical characteristics of individual InAs quantum dots (QDs) grown by metalorganic chemical vapor deposition, with low temperature emission in the telecoms window around 1300 nm. Using micro-photoluminescence (PL) spectroscopy we have identified neutral, positively charged, and negatively charged exciton and biexciton states. Temperaturedependent measurements reveal dot-charging effects due to differences in carrier diffusivity. We observe a pronounced linearly polarized splitting of the neutral exciton and biexciton lines (∼250 µeV) resulting from asymmetry in the QD structure. This asymmetry also causes a mixing of the excited trion states which is manifested in the fine structure and polarization of the charged biexciton emission; from this data we obtain values for the ratio between the anisotropic and isotropic electron-hole exchange energies of∆1/∆0 ≈ 0.2-0.5. Magneto-PL spectroscopy has been used to investigate the diamagnetic response and Zeeman splitting of the various exciton complexes. We find a significant variation in g-factor between the exciton, the positive biexciton, and the negative biexciton; this is also attributed to anisotropy effects and the difference in lateral extent of the electron and hole wavefunctions.

We have studied the emission properties of self-organized InAs quantum dots (QDs) grown in an InGaAs quantum well by metalorganic chemical vapor deposition. Low-temperature photoluminescence spectroscopy shows emission from single QDs around 1300 nm; we clearly observe the formation of neutral and charged exciton and biexciton states, and we obtain a biexciton binding energy of 3.1 meV. The dots exhibit an s-p shell splitting of approximately 100 meV, indicating strong confinement.Semiconductor self-assembled quantum dots (QDs) are of considerable interest for future telecommunication applications, such as low-threshold lasers and non-classical light sources for quantum key distribution systems. Efficient single-photon emission has recently been demonstrated at visible wavelengths using semiconductor QD structures, 1,2,3 and there have been many detailed investigations into the low-temperature optical characteristics of QDs emitting at 1150 nm or less. 4,5,6 However, to date there have been only a small number of spectroscopic experiments on single QDs emitting in the important telecommunications window around 1300 nm: 7 biexcitonic features have been identified in low-temperature photoluminescence (PL) from QDs grown by molecular beam epitaxy (MBE), 8 whereas similar investigations for QDs fabricated by metalorganic chemical vapor deposition (MOCVD) show an unclear power dependence in the emission. 9Quantum dot structures grown by MOCVD have potentially a large commercial value due to the high growth rates achievable; however, for applications at telecommunication wavelengths the growth is complicated by large strain effects and complex surface dynamics within the dot layers. 10 Therefore, there is a strong motivation for studying the optical characteristics of these structures in relation to other fabrication techniques. Here, we report on the emission properties of single QDs in a novel dotsin-well (DWELL) heterostructure grown by MOCVD. We present low-temperature PL spectra from individual QDs with an emission wavelength of 1300 nm; powerdependent measurements clearly reveal the formation of an exciton-biexciton system, with a biexciton binding energy of more than 3 meV. We also identify recombination from charged exciton and biexciton complexes, and we observe a large energy difference between s-and p-shell states.The QDs were fabricated using conventional lowpressure MOCVD on a (100) GaAs substrate: an InAs(:Bi) dot layer was deposited in a 5 nm In 0.12 Ga 0.88 As(:Bi) quantum well (QW), and the DWELL heterostructure grown between GaAs barrier layers and InGaP cladding layers. Bismuth doping was found to significantly improve the PL intensity and emission wavelength of the dots. The DWELL structure results in a pronounced red-shift relative to similar InAs/GaAs systems due to effects such as strain relaxation 11 and alloy decomposition. 12 Atomic force microscopy (AFM) measurements on similar samples suggest a dot size of < 15 nm with elongation along the [011] axis; the QD sheet density is estimated as 2 ...

We have studied the emission properties of individual InAs quantum dots (QDs) grown in an InGaAsP matrix on InP(100) by metal-organic vapor-phase epitaxy. Low-temperature microphotoluminescence spectroscopy shows emission from single QDs around 1550 nm with characteristic exciton-biexciton behavior, and a biexciton antibinding energy of more than 2 meV. Temperaturedependent measurements reveal negligible optical-phonon induced broadening of the exciton line up to 50 K, and emission from the exciton state clearly persists above 70 K. Furthermore, we find no measurable polarized fine structure splitting of the exciton state within the experimental precision. These results are encouraging for the development of a controllable photon source for fiber-based quantum information and cryptography systems.

Carrier relaxation processes have been investigated in GaAs/AlGaAs v-groove quantum wires (QWRs) with a large subband separation (∆E ≃ 46 meV). Signatures of inhibited carrier relaxation mechanisms are seen in temperature-dependent photoluminescence (PL) and photoluminescenceexcitation (PLE) measurements; we observe strong emission from the first excited state of the QWR below ∼50 K. This is attributed to reduced inter-subband relaxation via phonon scattering between localized states. Theoretical calculations and experimental results indicate that the pinchoff regions, which provide additional two-dimensional confinement for the QWR structure, have a blocking effect on relaxation mechanisms for certain structures within the v-groove. Time-resolved PL measurements show that efficient carrier relaxation from excited QWR states into the ground state, occurs only at temperatures > ∼ 30 K. Values for the low temperature radiative lifetimes of the ground-and first excited-state excitons have been obtained (340 ps and 160 ps respectively), and their corresponding localization lengths along the wire estimated.

We demonstrate lasing action with a high spontaneous emission factor and temperature insensitivity in InAs/InGaAs quantum dots (QD) embedded in photonic crystal nanocavities. A quality factor (Q) of over 10,000 was achieved by suppressing the material absorption by QDs uncoupled to the cavity mode. High Q cavities exhibited ultra low threshold lasing with a spontaneous emission factor of 0.7. Less frequent carrier escape from the QDs, which was primarily favored by high potential barrier energy, enabled low threshold lasing up to 90 K.