Emission characteristics of GaInN/GaN multiple quantum shell nanowire-based LEDs with different p-GaN growth conditions

Abstract

Improving current injection into r- and m-planes of nanowires (NWs) is essential to realizing efficient GaInN/GaN multiple quantum shell (MQS) NW-based light-emitting diodes (LEDs). Here, we present the effects of different p-GaN shell growth conditions on the emission characteristics of MQS NW-LEDs. Firstly, a comparison between cathodoluminescence (CL) and electroluminescence (EL) spectra indicates that the emission in NW-LEDs originates from the top region of the NWs. By growing thick p-GaN shells, the variable emission peak at around 600 nm and degradation of the light output of the NW-LEDs are elaborated, which is attributable to the localization of current in the c-plane region with various In-rich clusters and deep-level defects. Utilizing a high growth rate of p-GaN shell, an increased r-plane and a reduced c-plane region promote the deposition of indium tin oxide layer over the entire NW. Therefore, the current is effectively injected into both the r- and m-planes of the NW structures. Consequently, the light output and EL peak intensity of the NW-LEDs are enhanced by factors of 4.3 and 13.8, respectively, under an injection current of 100 mA. Furthermore, scanning transmission electron microscope images demonstrate the suppression of dislocations, triangular defects, and stacking faults at the apex of the p-GaN shell with a high growth rate. Therefore, localization of current injection in nonradiative recombination centers near the c-plane was also inhibited. Our results emphasize the possibility of realizing high efficacy in NW-LEDs via optimal p-GaN shell growth conditions, which is quite promising for application in the long-wavelength region.

Morphology Control and Crystalline Quality of p-Type GaN Shells Grown on Coaxial GaInN/GaN Multiple Quantum Shell Nanowires

“…In the case of core–shell NWs, a small region of the c -plane is inevitably formed at the tip area, which might affect the subsequent p-GaN shell growth and the performance of devices. As reported in our previous work, dislocations and pyramidal defects were identified in the p-GaN shell near the c -plane MQS with voids or serpentine morphology. , However, to our knowledge, the investigation of morphology control and crystalline quality for the entire p-GaN shell on MQS NWs is still lacking in the literature.…”

“…Dislocations and Mg clusters were observed in general p-GaN shells grown on the MQS NWs with low quality and voids at the c -plane region. , To gain insight into the structural features of the optimal p-GaN shell in the NW sample d, cross-sectional view STEM images (Z-contrast) were acquired along the growth direction [0001], as shown in Figure . From Figure a, the thicknesses of p-GaN on the m -, r -, and c -planes are estimated to be 365, 95, and 165 nm, respectively, corresponding to respective growth rates of 121, 31, and 55 nm/min.…”

“…As the injection current increased to 100 mA (4.0 kA/cm 2 ), an additional peak appeared at 450 nm, which is assignable to the emission component from the m -plane sidewall. This is because the MQS grown on a NW structure usually manifests a higher In concentration in the c -plane apex region than the r - and m -planes, , which has been confirmed by cathodoluminescence characterization at different positions of the MQS NW and the simulation method. , The expanded emission region from the top to bottom of r -planes caused the slight blue shift emission peak at 480 nm. Moreover, the emission peak from the c -plane area showed a blue shift from 510 to 500 nm induced by the QCSE phenomenon when the injection current was increased from 10 to 100 mA.…”

“…This is because NWs located outside of the mesa area are allowed to be selectively removed by ultrasonic cleaning. Despite the established growth approaches for MQS-NW structures and their advantages in fabricating devices, a uniform p-GaN shell with high crystalline quality is one of the essential factors for high-performance devices. , The quality of p-GaN is basically associated with the triangular defects or Mg clusters induced by high Mg doping concentration, which has been reported in core–shell MQS NWs. , Nevertheless, Mg doping likewise affects the morphology of GaN on patterned substrates owing to the Mg-induced anisotropic growth rates. , Different structure formations and Mg incorporations of p-GaN were observed in stacked NW structures using selective area growth by molecular beam epitaxy . In the case of core–shell NWs, a small region of the c -plane is inevitably formed at the tip area, which might affect the subsequent p-GaN shell growth and the performance of devices.…”

“…21,22 The quality of p-GaN is basically associated with the triangular defects or Mg clusters induced by high Mg doping concentration, which has been reported in core−shell MQS NWs. 23,24 Nevertheless, Mg doping likewise affects the morphology of GaN on patterned substrates owing to the Mg-induced anisotropic growth rates. 25,26 Different structure formations and Mg incorporations of p-GaN were observed in stacked NW structures using selective area growth by molecular beam epitaxy.…”