InP-based cylindrical microcavity light-emitting diodes

We have investigated the properties of InP-based microcavity light-emitting diodes (λ=1.6 μm). Our objective was mainly to study the effects of lateral confinement of optical modes, which was achieved by the wet oxidation of double In_0.52Al_0.48 As layers. The smallest devices had a cavity radius of 0.5 μm, which becomes comparable to λ/n, where n is the effective refractive index of the photon emitting heterostructure. Two types of devices were tested: the first without any mirrors in the vertical direction, and the second with a combination of MgF/ZnSe DBR (top) and silver (bottom) to produce a low Q~35-45. The latter type of devices exhibited higher output power and narrower spectral linewidth; otherwise, the characteristics were very similar The output slope efficiency monotonically decreases with reduction of lateral cavity size up to ~2-μm in diameter and then is enhanced again for smaller cavity sizes. The slope efficiency of the smallest device (aperture diameter 1 μm) is almost equal to that measured for the largest devices. The maximum output power measured from the devices is 30 μW. The far-field pattern of devices with aperture radii ranging from 1.5 to 20 μm shows an angular width (FWHM) of 50°. On the other hand, devices with smaller aperture (radius ~0.5 μm) exhibit an angular width of 20°. The measured small-signal modulation bandwidth increases from ~0.45 GHz for the larger devices to 0.8 GHz for the smallest devices. Our results indicate that microcavity effects can be observed with only lateral photon confinement, making device fabrication requirements less stringent compared to surface-emitting lasers