The Effect of Voltage-Dependent Charge-Removing Mechanism on the Optical Modulation Bandwidths of Light-Emitting Transistors

The optical modulation bandwidths of light-emitting transistors (LETs) at different bias conditions are measured and compared to investigate the influence of the voltage-dependent charge-removing mechanism within the active region. The modulation bandwidth dramatically increases from 338 MHz to 1.338 GHz when the transistor is operated from a saturation mode to a forward-active mode under a constant current of 2 mA. We show that gigahertz spontaneous bandwidths of LETs depend not only on the input currents, which is similar to light-emitting diodes, but are also strongly related to the voltages of a base-collector junction. By varying the reverse bias of the collector terminal, different charge distribution profiles can be established within the active region to perform distinct optical modulation bandwidths.