Increased electroluminescence from a two-junction Si n+pn CMOS structure

We have recently observed an increase in the visible electroluminescence from a two-junction Si npn CMOS structure. The device emit visible light in the 450 - 750 nm wavelength region at intensities up to 1 nW mum(-2) and operate at 8 - 20 V and 50 muA - 10 mA. The device utilizes the injection of electrons from a slightly forward biased and adjacently positioned pn junction into a second hot-carrier avalanching reverse-biased junction. The observed observation is explained in terms of a physical model that propose that direct interband recombination of low energy (cool) electrons recombine or interact with high energy (hot) carrier valance band holes in the silicon indirect bandgap structure. Although the emission is subsurface at this stage, the luminescence intensity appears to be about 250 times brighter than the luminescent intensity resulting from surface emitting Si pn avalanching junctions. The experimental observations and model predicts that the electrical-to-optical power conversion and quantum efficiencies as associated with present Si CMOS LED's may be increased by several orders of magnitude. The present levels of this Si LED is about three to four orders higher than the low frequency detectability of standard pn silicon detector utilizing the same area on chip.