No abstract

No abstract

No abstract

We present gain measurements and calculations for InAs/GaAs quantum dot injection lasers. Measurements of the modal gain and estimation of the confinement factor by transmission electron microscopy yield an exceptionally large material gain of 6.8(±1)×104 cm−1 at 80 A cm−2. Calculations including realistic quantum dot energy levels, dot size fluctuation, nonthermal coupling of carriers in different dots, and band filling effects corroborate this result. A large maximum differential gain of 2×10−12 cm2 at 20 A cm−2 is found. The width of the gain spectrum is determined by participation of excited quantum dot states. We record a low transparency current density of 20 A cm−2. All experiments are carried out at liquid nitrogen temperature.

No abstract

No abstract

By inserting stacked sheets of nominally 0.7 monolayer CdSe into a ZnSe matrix we create a region with strong resonant excitonic absorption. This leads to an enhancement of the refractive index on the low-energy side of the absorption peak. Efficient waveguiding can thus be achieved without increasing the average refractive index of the active layer with respect to the cladding. Processed high-resolution transmission electron microscopy images show that the CdSe insertions form Cd-rich two-dimensional (Cd, Zn)Se islands with lateral sizes of about 5 nm. The islands act as quantum dots with a three-dimensional confinement for excitons. Zero-phonon gain is observed in the spectral range of excitonic and biexcitonic waveguiding. At high excitation densities excitonic gain is suppressed due to the population of the quantum dots with biexcitons.

No abstract