Study of the Luminescence Decay of a Semipolar Green Light-Emitting Diode for Visible Light Communications by Time-Resolved Electroluminescence.

Time-resolved photoluminescence (TRPL) is often used to study the excitonic dynamics of semiconductor optoelectronics such as the carrier recombination lifetime of III-nitride light-emitting diodes (LEDs). However, for any real-world application that requires LEDs under electrical injection, TRPL suffers an intrinsic limitation due to the absence of taking carrier transport effects into account. This becomes a severe issue for III-nitride LEDs used for visible light communication (VLC) since the modulation bandwidth for VLC is determined by the overall carrier lifetime of an LED, not just its carrier recombination lifetime. Time-resolved electroluminescence (TREL), which can characterize the luminescence decay of an LED under electrical injection to simulate real-world conditions when used in practical applications, is required. Both TRPL and TREL have been carried out on a semipolar LED and a standard c-plane LED (i.e., polar LED) both in the green spectral region for a comparison study. The (11-22) green semipolar LED exhibits much faster differential carrier lifetimes than the c-plane LED. In addition to a fast exponential component and a slow exponential component of 0.40 and 1.2 ns, respectively, which are similar to those obtained by TRPL, a third lifetime of 8.3 ns due to transport-related effects has been obtained from TREL, which has been confirmed by capacitance measurements. It has been found that the overall carrier lifetime of a c-plane LED is mainly limited by RC effects due to a junction capacitance, while it is not the case for a semipolar LED due to intrinsically reduced polarization, demonstrating the major advantages of using a semipolar LED for VLC.