Light-emitting diode emission behaviors at a very weak injection current level are studied using the photon-counting method. It is observed that the emission is superlinearly dependent on the injection current irrespective of the emitting wavelength. The bending point of the L:I plot is different from that of the V:I plot. The bimolecular emission nature is interpreted to be a nonradiative transition mechanism due to some deep level trapping.
"Superlinear emission of light-emitting diodes at very low current excitation," Optical Engineering 33(2), (1 February 1994). http://dx.doi.org/10.1117/12.153130