A nitride-based light-emitting structure composed of a GaN nanowire core and GaInN/GaN multi-quantum shells (MQSs) is promising for high performance optoelectronic devices. By growing high crystalline quality MQS on the nonpolar (m-plane) sidewall of the nanowires, an improvement of luminous efficiency is expected. For Mg activation in p-GaN under the tunnel junction is a big challenge, in this work, we carried out the sputtering growth of n-GaN capping layer on the tunnel junction/p-GaN/MQS/nanowire structures for the first time. Single crystalline n-GaN was successfully grown mainly on the tip of the nanostructures.
Current injection through tunnel junctions (TJs) can enhance the external quantum efficiency of nanowire (NW) and multi-quantum-shell-based optical devices, compared. However, control of the impurity concentration profile is difficult in such tiny structure. In this study, we show a simple evaluation method of impurities in TJs growing flatly on m-plane GaN substrates, which have the same crystalline orientation as the luminescent surface of MQS/NWs. It was found to decrease the differential resistance by increase the concentration of Mg in p^(++)-GaN in the TJ.
GaInN/GaN multi-quantum shells nanowires (NWs) are coaxially grown in non-polar m-plane or semi-polar r-plane surface, which is expected to improve the luminous efficiency. The emission wavelengths usually redshift from the sidewall to top c-plane region. However, the emission from c-plane has low luminous efficiency. In this research, the c-plane area of NWs in one sample was removed by dry etching prior to the fabrication process, while the other one without c-plane etching was prepared to investigate the effect of c-plane region on the luminescence intensity. The sample with etching shows 12 times higher output power than the sample without etching.
GaInN/GaN multiple quantum shells (MQS) nanowires and p-GaN shells were embedded with n-GaN layers through tunnel junction (TJ) shells using metalorganic chemical vapor deposition (MOCVD) method. The MQS nanowires were selectively grown on n-GaN/sapphire or GaN substrates. The fabrication process of laser structures with different resonators of 600500, 750, 1000 μm, and cavity widths of 7, 12, and 17 μm were investigated with insulating layer on the sidewalls of the ridge. The structures of the fabricated devices were characterized by scanning electron microscope (SEM) and current-voltage-light output characteristics were evaluated. Two different methods for mirror formation, etching and cleavage, were developed for the laser devices. During the investigation, a superior mirror formation suffered from the difference in etching rate between GaInN and GaN, generating concaves in the MQS region. Bluegreen light emission was observed from the entire ridge surface of the MQS index-guided laser structures. A maximum current density of emission at 17.9 kA/cm2 has been confirmed in the devices. The electroluminescence and cathodoluminescence measurements demonstrated that the r-plane and c-plane at the top of the MQS are dominant at low current densities, and the m-plane emission becomes stronger as the current density increases.
A tunnel junction and a n-GaN cap layer grown on the multi-quantum shells (MQS) /nanowires are introduced to decrease the resistivity and optical loss. The selective-area growth of the MQS/nanowire core-shell structures on the template was performed by metalorganic vapour phase epitaxy (MOVPE). Further, the MQS structure was covered with the tunnel junction and the n-GaN cap layer. Here, the growth conditions of the n-GaN cap layer were systemically investigated. The effect of p-GaN shape on the morphology of grown n-GaN cap layer was also assessed.
The selective-monolithic growth of coaxial GaInN/GaN NWs was investigated by changing the TEG flow rate, barrier and well growth temperature during MQS growth. In incorporation increased with a higher TEG flow rate. However, In-rich flakes were formed the NWs resulting in the deterioration of crystal quality. Using a higher growth temperature of quantum barriers, abnormal growth at the top of NWs was eliminated. As a result, the CL emission intensity was enhanced. Furthermore, the occurrence of In desorption was suppressed by decreasing the growth temperature of quantum wells. Therefore, these results are promising for NW-based white LEDs.
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