Enhancement in light efficiency of a GaN:Eu red light-emitting diode by pulse-controlled injected charges

An electrical resonance technique was developed to enhance the emission efficiency of a light-emitting diode (LED) with a low density of dopants as the luminescence centers. A rectangular pulse drive, tuned to the frequency corresponding to the electrical time constant of the LED active layer, intensified the emission of a GaN:Eu red LED. The injected charge carriers, which are transported back-and-forth in the active layer (“back-and-forth transport”), can effectively excite the Eu luminescence centers. A wide scan of the rectangular pulse frequencies revealed injected charge behavior in the active layer. At low frequencies, the injected charges penetrated through the active layer and were lost outside of it (“external loss”), whereas localized back-and-forth motion of the injected charges occurred at high frequencies without interaction with the Eu dopants in the active layer (“internal loss”). An intermediate frequency, at which the sum of the external and internal losses was minimized, yielded the optimal electrical resonance for intensification.