  The quality factor (Q), mode volume (Veff), and room-temperature 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 Veff can be as small as 2(lambda/n)^3 while
maintaining radiation-limited Qs in excess of 10^5. Microdisks of diameter D=2
microns are fabricated in an AlGaAs material containing a single layer of InAs
QDs with peak emission at lambda = 1317 nm. For devices with Veff ~2
(lambda/n)^3, Qs as high as 1.2 x 10^5 are measured passively in the 1.4 micron
band, using an optical fiber taper waveguide. Optical pumping yields laser
emission in the 1.3 micron band, with room temperature, continuous-wave
thresholds as low as 1 microWatt 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 laser differential efficiency as high as xi~16% and
out-coupling efficiency in excess of 28%.
