Jongjin Jang

Regrowth of Semipolar GaN on Nanoporous GaN Template by Metal Organic Chemical Vapor Deposition

A nanoporous semipolar GaN template has been fabricated by photoenhanced electrochemical etching to obtain porous GaN with nanoscale pores. The surface morphology of regrown semipolar GaN on a nanoporous GaN template was enhanced by surface modification. Cross-sectional transmission electron microscopy (TEM) images showed reductions in the densities of dislocations and basal stacking faults at the regrown interface. Photoluminescence measurement also revealed that the crystallinity of regrown GaN was improved by reducing the density of defects. Our results suggest that the photoenhanced electrochemical etching and regrowth technique is promising for high-quality semipolar GaN growth with a reduced defect density on a sapphire substrate.

Phosphor-free white-light emitters using in-situ GaN nanostructures grown by metal organic chemical vapor deposition.

Realization of phosphor-free white-light emitters is becoming an important milestone on the road to achieve high quality and reliability in high-power white-light-emitting diodes (LEDs). However, most of reported methods have not been applied to practical use because of their difficulties and complexity. In this study we demonstrated a novel and practical growth method for phosphor-free white-light emitters without any external processing, using only in-situ high-density GaN nanostructures that were formed by overgrowth on a silicon nitride (SiNx) interlayer deposited by metal organic chemical vapor deposition. The nano-sized facets produced variations in the InGaN thickness and the indium concentration when an InGaN/GaN double heterostructure was monolithically grown on them, leading to white-color light emission. It is important to note that the in-situ SiNx interlayer not only facilitated the GaN nano-facet structure, but also blocked the propagation of dislocations.

Inclined angle-controlled growth of GaN nanorods on m-sapphire by metal organic chemical vapor deposition without a catalyst

In this study, we have intentionally grown novel types of (11-22)- and (1-10-3)-oriented(3) and self-assembled inclined GaN nanorods (NRs) on (10-10) m-sapphire substrates using metal organic chemical vapor deposition without catalysts and ex situ patterning. Nitridation of the m-sapphire surface was observed to be crucial to the inclined angle as well as the growth direction of the GaN NRs. Polarity-selective KOH etching confirmed that both (11-22) and (1-10-3) GaN NRs are nitrogen-polar. Using pole figure measurements and selective area electron diffraction patterns, the epitaxial relationship between the inclined (11-22) and (1-10-3) GaN NRs and m-sapphire substrates was systematically demonstrated. Furthermore, it was verified that the GaN NRs were single-crystalline wurtzite structures. We observed that stacking fault-related defects were generated during the initial growth stage using high-resolution transmission electron microscopy. The blue-shift of the near band edge (NBE) peak in the inclined angle-controlled GaN NRs can be explained by a band filling effect through carrier saturation of the conduction band, resulting from a high Si-doping concentration; in addition, the decay time of NBE emission in (11-22)- and (1-10-3)-oriented NRs was much shorter than that of stacking fault-related emission. These results suggest that defect-free inclined GaN NRs can be grown on m-sapphire without ex situ treatment.

Study of enhanced photovoltaic behavior in InGaN-based solar cells by using SiNx insertion layer: Influence of dislocations

Using a SiNx insertion layer to reduce dislocations, enhanced photovoltaic properties could be obtained in p?i?n InGaN/GaN heterojunction solar cell. To investigate the influence of the dislocations on the photovoltaic behaviors, a sample grown without SiNx insertion layer was identically prepared for comparison. From optical properties measurements, the reduction in the number of non-radiative centers and a stronger In localization effect was shown in the sample with SiNx insertion layer. However, the quantum confined stark effect was almost negligible in both the samples. Electrical properties measurement showed reduced saturation current and increased shunt resistance in the sample with SiNx insertion layer due to the reduced dislocation density. By comparing these results and using a numerical model, the influence of the dislocation density on the different photovoltaic properties such as open-circuit voltage and fill factor has been confirmed.

Correlation between luminescence and defects in nonpolar and semipolar InGaN/GaN quantum wells on planar and patterned sapphire substrates

The optical and structural properties of nonpolar and semipolar InGaN/GaN quantum wells (QWs) grown on planar sapphire substrates and patterned sapphire substrates (PSSs) were investigated in order to understand the effect of defects on the luminescence. By introducing the PSS technique, surface morphological features were varied in number and size, and the defect density was significantly reduced by the PSS patterns, which resulted in the formation of low-defect regions. The photoluminescence (PL) analyses of nonpolar and semipolar QWs samples revealed that the semipolar

Comparison between the relaxation mechanisms of thick (0001) polar and

(11\bar 22)

semipolar InGaN layers

QWs, which had better optical performance and higher In incorporation, are more suitable for application to long-wavelength emitters in the green-red spectral range and beyond. Moreover, particularly in the semipolar QWs, we could observe that the optical properties were enhanced by the decrease in defect density. It was also noted that In incorporation was increased in the high-defect regions and in the regions where arrowhead-like features existed.

Strain relaxation of thick (11–22) semipolar InGaN layer for long wavelength nitride-based device

In this study, self-assembled inclined (1-10-3)-oriented GaN nanorods (NRs) were grown on nanoimprinted (10-10) m-sapphire substrates using catalyst-free metal-organic chemical vapor deposition. According to X-ray phi-scans, the inclined GaN NRs were tilted at an angle of ∼57.5° to the [10-10]sapp direction. Specifically, the GaN NRs grew in a single inclined direction to the [11-20]sapp. Uni-directionally inclined NRs were formed through the one-sided (10-11)-faceted growth of the interfacial a-GaN plane layer. It was confirmed that a thin layer of a-GaN was formed on r-facet nanogrooves of the m-sapphire substrate by nitridation. The interfacial a-GaN nucleation affected both the inclined angle and the growth direction of the inclined GaN NRs. Using X-ray diffraction and selective area electron diffraction, the epitaxial relationship between the inclined (1-10-3) GaN NRs and interfacial a-GaN layer on m-sapphire substrates was systematically investigated. Moreover, the inclined GaN NRs were observed to ...