Optical Power Efficiency Versus Breakdown Voltage of Avalanche-Mode Silicon LEDs in CMOS

We report on the dependency of the optical power efficiency η on the breakdown voltage VBR of avalanche-mode (AM) light-emitting diodes (LEDs) in silicon. Lateral p
⁺
-n-n
⁺
LEDs have been designed in a 65-nm bulk CMOS technology, where VBR is varied between 2 and 9 V. This tunes both the magnitude and the spatial distribution of the reverse electric field, which governs AM electroluminescence. Experiments show that a maximum η of ~1.7 × 10
^-6
is obtained for V
_BR
~ 6 V. For V
_BR
<; 6 V, non-local avalanche results in a lower η, while for V
_BR
> 6 V, a gradual reduction in η with increasing VBR is obtained. This trend is compared with two recently proposed opto-electronic models. A maximum in η at relatively low voltages is attractive for monolithic opto-electronic integration in silicon.