Low-Voltage CMOS/BiCMOS Light Emitting Devices

Low-voltage Si-LED operation can be achieved by fabricating devices with heavily doped n
⁺
p
⁺
junctions. Differences are observed between high-voltage avalanche and low-voltage field emission LED performance. The low-voltage devices exhibit a non-linear light intensity L vs. reverse current I relationship at low current levels, but a linear dependency at higher currents, compared to the linear behavior of avalanche devices at all current levels. Three regions of operation are identified for the low-voltage field emission LED's, namely L prop I
³
at low currents, L prop I
²
at medium currents and eventually L prop I at higher currents. In the low-voltage non-linear region of operation, the shape of the emitted spectrum changes with reverse current. At low reverse current the field emission devices emit more long wavelength radiation than short wavelength radiation. As the reverse current increases, the short wavelength radiation increases relative to the long wavelength radiation, and at higher currents in the linear region of operation the ratio between long and short wavelength radiation remains constant