Crystal Growth and Characterization of n-GaN in a Multiple Quantum Shell Nanowire-Based Light Emitter with a Tunnel Junction

Abstract

Here, we systematically investigated the growth conditions of an n-GaN cap layer for nanowire-based light emitters with a tunnel junction. Selective-area growth of multiple quantum shell (MQS)/nanowire core−shell structures on a patterned n-GaN/sapphire substrate was performed by metal− organic vapor phase epitaxy, followed by the growth of a p-GaN, an n ++ / p ++ -GaN tunnel junction, and an n-GaN cap layer. Specifically, two-step growth of the n-GaN cap layer was carried out under various growth conditions to determine the optimal conditions for a flat n-GaN cap layer. Scanning transmission electron microscopy characterization revealed that n ++ -GaN can be uniformly grown on the m-plane sidewall of MQS nanowires. A clear tunnel junction, involving 10-nm-thick p ++ -GaN and 3-nm-thick n ++ -GaN, was confirmed on the nonpolar m-planes of the nanowires. The Mg doping concentration and distribution profile of the p ++ -GaN shell were inspected using three-dimensional atom probe tomography. Afterward, the reconstructed isoconcentration mapping was applied to identify Mg-rich clusters. The density and average size of the Mg clusters were estimated to be approximately 4.3 × 10 17 cm −3 and 5 nm, respectively. Excluding the Mg atoms contained in the clusters, the remaining Mg doping concentration in the p ++ -GaN region was calculated to be 1.1 × 10 20 cm −3 . Despite the lack of effective activation, a reasonably low operating voltage and distinct light emissions were preliminarily observed in MQS nanowire-based LEDs under the optimal n-GaN cap growth conditions. In the fabricated MQS-nanowire devices, carriers were injected into both the r-plane and m-plane of the nanowires without a clear quantum confinement Stark effect.

Demonstration of GaN:Eu/GaN nanowire light emitting diodes grown by selective-area organometallic vapor phase epitaxy

“…So far, there have been several demonstrations of NW-based photonic devices including light emitters such as nano lasers, 18) photoniccrystal-based lasers, 19,20) photovoltaics, 21) photodetectors, 22) and temperature sensors. 23) In addition, several types of NW LEDs were reported in stable structures [24][25][26][27][28] and flexible structures, [29][30][31][32][33] including red LEDs based on GaN:Eu grown on GaN NWs with top structures of continuous film 34) and red flexible LEDs based on GaPAs/GaP NWs. 35) Our group has so far reported the formation of core-shell-type GaN:Eu/GaN NWs grown by OMVPE and observed a sharp red luminescence, 36) which would be applicable for flexible LEDs by transferring the NWs in flexible membranes.…”

Selective-Area Growth Mechanism of GaN Microrods on a Plateau Patterned Substrate

“…The reasons for this large amount of attention on the microstructure of III-nitrides include the elimination of the quantum confined stark effect (QCSE) [ 3 , 4 ], the reduction of threading dislocation density [ 5 , 6 , 7 ], and the reduction of the internal stress in the epi-structure [ 8 , 9 ]. Due to these advantages, the microstructures of III-nitride materials have been widely used in optoelectronics and high-speed electronics, including light-emitting diodes (LEDs) [ 10 , 11 ], energy harvesting applications, and high-electron mobility transistors (HEMT). Particularly, gallium nitride (GaN) has attracted attention as a next-generation semiconductor material owing to its wide band gap (3.41 eV), high electron mobility in the two-dimensional electron gas in the HEMT, and high thermal stability.…”

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

“…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.…”