Spectral characteristics of low threshold microdisks

Semiconductor microdisks present a device with interesting physics but without an obvious practical application. The 'conventional' microdisk structure uses a pedestal to hold the boundary of a semiconductor disk in air leading to essentially a parallel array of edge emitters. We form disks by epitaxial lift-off which opens up several possibilities, as, in the use of a disk as an evanescent wave, in plane waveguide filter in silica based waveguides or as arrays of vertical emitters by placing the disks on reflectors. Arrays are of thin (150-700 nm) semiconductor (InGaAsP, /spl lambda/g = 1.55 /spl mu/m at room temperature) disks and rings on glass substrates. To date work has concentrated on disk thickness < /spl lambda//2n due to the microcavity effect of enhanced coupling of spontaneous emission to waveguide modes. We have measured lasing in disks with thickness significantly greater than /spl lambda//2n.