Enhanced Radiative Recombination Rate by Local Potential Fluctuation in InGaN/AlGaN Near-Ultraviolet Light-Emitting Diodes  
[PERSON]  
1 Department of Electronics and Communication Engineering, Hanyang University ERICA, Ansan 15588, Korea; [EMAIL_ADDRESS]  
[PERSON]  
223  
However, the efficiencies of these QWs turn out to be surprisingly high despite high-density defects [13; 16]. It has been suspected that such high efficiencies are caused by the localization of carriers by the potential-energy fluctuation in the QWs, which prevents the carriers from recombining nonradiatively at defects [13; 16; 17]. The possible reasons reported for carrier localization include alloy fluctuation with the incorporation of In [18; 19; 20; 21], thickness variation of QWs [20; 21], In-N-In chains [22], In clustering [23], crystal quality [24], In/Ga segregation [17], crystallographic defects [14; 25; 26; 27; 28], the piezoelectric field (\(F_{\text{PZ}}\)) [21; 28; 29], and the combined effects of point defects and \(F_{\text{PZ}}\)[30]. It has been widely accepted that excited carriers are spatially separated from defects owing to higher electrical potential energy at the edge of defects, which prevents carriers from diffusing into them [13; 16; 25; 26; 30]. Carriers thus radiatively recombine at the nondefective region, which increases the efficiencies of LEDs.  
The efficiency decreases are due to Shockley-Read-Hall (SRH) recombination or tunneling leakage through defects at low currents, and carrier overflow initiated by saturation phenomena at high currents. The carrier overflow from the QWs can be decreased by effectively designing the barriers [2; 31; 2; 31]. At low currents, quantum efficiency increases when the defect density in the active region becomes small. However, it is almost impossible to completely eliminate defects from the InGaN-based QWs grown on sapphire substrates. Thus, it is necessary to understand how defects influence radiative recombination and affect the optoelectronic performance of LEDs.  
Therefore, in this study, we utilized NUV LED samples with different In compositions without any specially designed barrier to comprehend the increase in radiative recombination rates at low currents where defects play an important role. We found that the increase in radiative recombination rates at low currents was owing to spatial localization of carriers caused by the local potential-energy fluctuation in QWs [17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29] that originated from the combined effects of point defects, \(F_{\text{PZ}}\), and In compositions.  
There has been research investigating the potential-energy fluctuation through material characterization and numerical simulations [17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29]. However, there still exists a lack of comprehensive research work using macroscopic characterizations to understand the potential-energy fluctuation in QWs. Therefore, in this work, we reported on the effects of local potential-energy fluctuation in InGaN/AlGaN MQWs that influence device performance by using a proposed carrier recombination model. We employed various kinds of macroscopic characterization techniques such as current-voltage (_I-V_), ideality factor (\(n\)), peak wavelength (\(\lambda_{\text{p}}\)), light output power vs. current (_L-I_), internal quantum efficiency (IQE), two-dimensional photoemission-microscopy (PHEMOS), electroluminescence (EL) and electroreflectance (ER) characteristics to identify the potential-energy fluctuation and assess the performance of these LEDs.