  We report an easy-to-fabricate microcavity design to produce optically pumped
high-$\beta$ quantum dot microlasers. Our cavity concept is based on a buried
photonic-defect for tight lateral mode confinement in a quasi-planar
microcavity system, which includes an upper dielectric distributed Bragg
reflector (DBR) as a promising alternative to conventional III-V semiconductor
DBRs. Through the integration of a photonic-defect, we achieve low mode volumes
as low as 0.28 $\mu$m$^3$, leading to enhanced light-matter interaction,
without the additional need for complex lateral nanoprocessing of micropillars.
We fabricate semiconductor-dielectric hybrid microcavities, consisting of
Al$_{0.9}$Ga$_{0.1}$As/GaAs bottom DBR with 33.5 mirror pairs, dielectric
SiO$_{2}$/SiN$_x$ top DBR with 5, 10, 15, and 19 mirror pairs, and
photonic-defects with varying lateral size in the range of 1.5 $\mu$m to 2.5
$\mu$m incorporated into a one-$\lambda/n$ GaAs cavity with InGaAs quantum dots
as active medium. The cavities show distinct emission features with a
characteristic photonic defect size-dependent mode separation and
\emph{Q}-factors up to 17000 for 19 upper mirror pairs in excellent agreement
with numeric simulations. Comprehensive investigations further reveal lasing
operation with a systematic increase (decrease) of the $\beta$-factor
(threshold pump power) with the number of mirror pairs in the upper dielectric
DBR. Notably, due to the quasi-planar device geometry, the microlasers show
high temperature stability, evidenced by the absence of temperature-induced
red-shift of emission energy and linewidth broadening typically observed for
nano- and microlasers at high excitation powers.
