The lasers studied were GaAs/AlGaAs structures with monolithic semiconductor DBRs and oxide layers on both sides of the active region. The active layer was composed of five 8 nm GaAs quantum wells contained in a 
cavity. The monolithic DBRs are quarter wave thick pairs of Al0.16Ga0.84As/Al0.92Ga0.08As with 25 pairs in the top DBR. The thin (18 nm) Al0.98Ga0.02As oxide confinement layers were embedded in low index quarter-wave layers 3 mirror periods from the active region. The aim of this design was to reduce the overlap between the field and the apertures and thus reduce aperture scattering [62], a factor implicated in the higher threshold gain of smaller devices [60]. A series of lasers with different mesa sizes ranging from 30 
m to 70 m was fabricated by etching square mesas through the active layer with reactive ion etching and oxidising laterally the high Al content layer [55]. The difference in side length between successive mesas was 0.5 m, making available lasers with side lengths between <0.5 m and 10 m in 0.5 m steps.
On a cryogenic stage the devices lased with heat sink temperatures ranging from 100 K to 400 K with a minimum threshold around 300 K. Measurements of the polarisation properties of small (
m aperture sidelength), single mode devices suggests that the sample is strained, as a single polarisation is maintained to within 
over the entire temperature range, and across the wafer the same polarisation is found for all devices.
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