InP-based cylindrical microcavity light-emitting diodes

We have investigated the properties of InP-based microcavity light-emitting diodes (/spl lambda/=1.6 /spl mu/m). Our objective was mainly to study the effects of lateral confinement of optical modes, which was achieved by the wet oxidation of double In/sub 0.52/Al/sub 0.48/As layers. The smallest devices had a cavity radius of 0.5 /spl mu/m, which becomes comparable to /spl lambda//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/spl sim/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 /spl sim/2-/spl mu/m in diameter and then is enhanced again for smaller cavity sizes. The slope efficiency of the smallest device (aperture diameter 1 /spl mu/m) is almost equal to that measured for the largest devices. The maximum output power measured from the devices is 30 /spl mu/W. The far-field pattern of devices with aperture radii ranging from 1.5 to 20 /spl mu/m shows an angular width (FWHM) of 50/spl deg/. On the other hand, devices with smaller aperture (radius /spl sim/0.5 /spl mu/m) exhibit an angular width of 20/spl deg/. The measured small-signal modulation bandwidth increases from /spl sim/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.