The lowest room-temperature threshold current density, 26A/cm 2 , of any semiconductor diode lasers is reported for a quantum dot device with a single InAs dot layer contained within a strained In 0.15 Ga 0.85 As quantum well. The lasers are epitaxially grown on a GaAs substrate, and the emission wavelength is 1.25 µ m.

Abstract:The quality factor (Q), mode volume (V eff ), and roomtemperature lasing threshold of microdisk cavities with embedded quantum dots (QDs) are investigated. Finite element method simulations of standing wave modes within the microdisk reveal that V eff can be as small as 2(λ/n) 3 while maintaining radiation-limited Qs in excess of 10 5 . Microdisks with a 2 µm diameter are fabricated in an AlGaAs material containing a single layer of InAs QDs with peak emission at λ = 1317 nm. For devices with V eff ∼2 (λ/n) 3 , Qs as high as 1.2×10 5 are measured passively in the 1.4 µm band, using an optical fiber taper waveguide. Optical pumping yields laser emission in the 1.3 µm band, with room temperature, continuous-wave thresholds as low as 1 µW of absorbed pump power. Out-coupling of the laser emission is also shown to be significantly enhanced through the use of optical fiber tapers, with a laser differential efficiency as high as ξ ∼ 16% and out-coupling efficiency in excess of 28% measured after accounting for losses in the optical fiber system.

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