n-type GaN surface etched green light-emitting diode to reduce non-radiative recombination centers

Abstract

In this study, we attempt to identify the presence of surface defects (SDs) at an n-type GaN surface after high-temperature growth and gain insight into their intrinsic features. To this end, first, we carefully investigate n-type GaN samples with different surface etching depths. Low-temperature photoluminescence (PL) spectra reveal that SDs are most likely nitrogen vacancies (VN) and/or VN-related point defects intensively distributed within ∼100 nm from the n-type GaN surface after a high-temperature growth. We investigate the effect of SDs on the internal quantum efficiency (IQE) of green light-emitting diodes (LEDs) by preparing GaInN-based green LEDs employing a surface-etched n-type GaN, which exhibits a prominent enhancement of the PL efficiency with an increase in the etching depth. This effect is attributable to the reduced non-radiative recombination centers in multiple-quantum-well active regions because the SDs near the n-type GaN surface are removed by etching. We discuss strategies of in situ engineering on SDs to further improve the IQE in GaInN-based green LEDs on the basis of the results presented in this study.

Imaging Nonradiative Point Defects Buried in Quantum Wells Using Cathodoluminescence

“…Other macroscale studies have also detected two types of PDs in InGaN/GaN QWs. 17,19 Evidence suggests midgap (type-I) defects are intrinsic nitrogen vacancy complexes, 21,40 while the type-II defect may be linked to impurities such as oxygen or carbon. 41 All these results highlight the versatility of our CL analysis to extract this information directly from images of PDs, and have particular relevance for III-nitride devices based on InGaN.…”

“…Furthermore, their results also associate these defects with a near-midgap energy level and identify another energy level near the valence band edge which could match our type-II defects. Other macroscale studies have also detected two types of PDs in InGaN/GaN QWs. , Evidence suggests midgap (type-I) defects are intrinsic nitrogen-vacancy complexes, ,, whereas the type-II defect may be linked to impurities such as oxygen or carbon …”

“…Other macroscale studies have also detected two types of PDs in InGaN/GaN QWs. 17,19 Evidence suggests midgap (type-I) defects are intrinsic nitrogen-vacancy complexes, 21,22,37 whereas the type-II defect may be linked to impurities such as oxygen or carbon. 38 Having characterized these nonradiative PDs, we now investigate how their density impacts the carrier diffusion length in the well, which is a critical parameter for the performance of optoelectronic devices such as micro-LEDs.…”

Application of patterned sapphire substrate for III-nitride light-emitting diodes

“…92 In particular, dislocations and point defects serve as nonradiative recombination centres that introduce the defect levels into the bandgap of III-nitrides and reduce the possibility of radiative recombination by capturing carriers, finally degrading the IQE of LEDs. [93][94][95][96] Moreover, fundamental bottlenecks including efficiency droop 97 and green gap 98 encountered by III-nitride LEDs are found to be closely related with dislocation density, which adversely affects IQE and thus degrades optoelectronic properties of LED devices.…”

Pre-trimethylindium Flow Treatment of GaInN/GaN Quantum Wells to Suppress Surface Defect Incorporation and Improve Efficiency

“…Several physical mechanisms have been suggested as the origin of the green gap, including the quantum-confined Stark effect, random alloy fluctuation, high dislocation density, and asymmetric carrier distribution. − Besides these, the high level of defect incorporation in the multiple-quantum-well (MQW) active layer has often been discussed as a potential contributor to the green gap. Recent studies have revealed that the defect incorporation originated from two independent mechanisms: (i) inherent incorporation of impurities, such as carbon and oxygen, due to reduction in the growth temperature to grow the indium (In)-rich MQWs , and (ii) incorporation of the native defects formed at an n-type GaN surface [i.e., surface defects (SDs)] into the MQWs during the LT growth. − Both mechanisms create nonradiative recombination centers (NRCs) in the MQW active layer, which act as a path for Shockley–Read–Hall (SRH) nonradiative recombination, thereby reducing IQE. , Recently, studies on the second of the above-mentioned mechanism are being actively conducted by several research groups as it is considered a key factor in the IQE improvement. − Our recent studies showed that the SDs in an n-type GaN are most likely nitrogen vacancies (V N ), divacancies comprising Ga and N vacancies (V Ga V N ), and/or a V N impurity complex, which are intensively distributed within about 100 nm from the growth surface of n-type GaN. , Note that the SDs are easily incorporated with In atoms owing to strong affinity between them; therefore, an introduction of a GaInN or AlInN layer between the n-type GaN and the MQWs [i.e., an underlying layer (UL)] is very useful to improve the IQE by trapping the SDs therein. , However, a further increase in the In content and/or thickness of the UL to enhance the SD trapping frequently has negative impacts on the device performance because it generates threading dislocations (TDs) and absorbs the photons emitted from the MQWs. , This indicates that the introduction of a UL alone is insufficient to suppress the incorporation of SDs into the MQWs. As a method to further reduce the SDs in n-type GaN other than the introduction of a UL, we have demonstrated the MQWs grown on the surface-etched n-type GaN layer, which showed an improvement in the IQE by a factor of 2.5 in green LEDs .…”