Planar, Fast, Reliable, Single-Heterojunction Light-Emitting Diodes for Optical Links

In a recent publication 1 we reported on a broad-area (junction area extending over the full area of the chip), low-current-density, simplegeometry L E D with exceptional reliability. These broad-area LEDS, at 67 A/cm 2 current density, launched 30 juW of butt-coupled optical power into a fiber with 0.36 numerical aperture (NA) and a 125-jum 1549 core diameter 2 and were used as sources in prototype optical-link electronic switching systems with low optical power requirements. 3 In this paper, we report on planar LEDS, i.e., devices which consist totally of material grown by liquid phase epitaxy (LPE). This device structure eliminates the need for the etched well, characteristic of Burrus-type devices, 4 resulting in over 90-percent device fabrication yield. Uniform material of 7.0 cm 2 can be grown on a substrate during a single crystal growth run yielding ~1500 LEDS. These LEDS launch 100 /xW of butt-coupled optical power into a 0.36-NA, 125-jum corediameter fiber and 10 /iW into a fiber with 0.23 NA and 55-/zm core diameter. T h e improvements over the broad area device result from current crowding by contact area restriction (from full area to 50-/im diameter dot) to increase the current density (from 67 A/cm 2 to 700 A/cm 2 ) for increased brightness. Furthermore, the localized emission region couples the light more efficiently into the fiber. This simple LED structure, which can be grown on large areas and fabricated with high yield, is exceptionally reliable with predicted failure rates of 1 FIT for a 40-year service life.