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.

时间分辨光致发光（TRPL）常被用于研究半导体光电子器件的激子动力学，比如III - 氮化物发光二极管（LED）的载流子复合寿命。然而，对于任何需要电注入下的LED的实际应用而言，由于没有考虑载流子输运效应，TRPL存在一个固有局限。这对于用于可见光通信（VLC）的III - 氮化物LED来说是一个严重的问题，因为VLC的调制带宽是由LED的总载流子寿命决定的，而不仅仅是其载流子复合寿命。时间分辨电致发光（TREL）能够表征电注入下LED的发光衰减，以模拟实际应用中的实际条件，这是必需的。在绿色光谱区域对一个半极性LED和一个标准的c面LED（即极性LED）都进行了TRPL和TREL测量以作比较研究。（11 - 22）绿色半极性LED展现出比c面LED快得多的差分载流子寿命。除了分别为0.40纳秒和1.2纳秒的快指数成分和慢指数成分（这与通过TRPL获得的结果相似），通过TREL还获得了由于输运相关效应产生的8.3纳秒的第三个寿命，这已通过电容测量得到证实。研究发现，c面LED的总载流子寿命主要受结电容导致的RC效应限制，而对于半极性LED由于其固有极化减小则并非如此，这表明了在VLC中使用半极性LED的主要优势。