Edge-emitting Si avalanche-mode LED integrated into a SiGe RF bipolar technology: Optical power emission characterization with optical probe mapping technique

A novel silicon SiGe edge light emitting diode (SiGe ELED) was realized in standard RF bipolar SiGe technology process that uses a p-n junction either in reverse and forward bias mode configurations. A vertical cubical columnar SiGe/Si HBT like structure was used. The light emitting process in the reverse bias mode is by means of an avalanche breakdown process. The reverse biased device emits light in the wavelength range of 450-650 nm, with operating voltage and current of 1.3 V and 8 mA respectively, while the forward biased mode emitted at about 850nm. In the forward biased mode, it operates in a two junction mode with the first n+p junction emitting low energy electrons into a lowly doped p region. The SiGe ELED is intended to be implemented in an optical interconnect with an external detector via a lateral optical waveguide coupling. Because the LED emit in a broad spectrum, localizing the emission source point is of paramount importance. Two techniques were used to attempt to realise this objective. Optical Probe measurement and Optical Power Meter Mapping technique. Localization of the emission source point process was performed through scanning a lensed fiber coupled to an optical power meter, over the edge surface profile of the diced device. The side edge of the diced device structure was interface with the lens fibre in other to ascertain the maximum emission point and the nature of light emitting process. This was done using a smooth dicing of the LED device close to its emitting edge and scanning its edge surface through a multimode lensed fiber coupled to an optical power meter. The mapping area scanned was 40μm x 40μm and 60μ x 60μ to localize the emitting source point region. A total emitted optical power as measured from the Led was 2.86nW as measured by the optical power meter connected to the lensed optical fibre. This was confirmed with a light-current-voltage (LIV) characteristics power measurement curve obtained from the device by means of the edge mapping techniques. A rough estimated localization of the source point was approximately 0.3mW optical power with a current of 8mA was realized with this technique. These results can be used to design accurate electro-optical conversions in integrated photonic circuitry as well as designing well coupled optical interconnects from the chip to the environment.