The authors fabricated GaN-based light-emitting diodes (LEDs) on two different GaN templates with the same LED structure. One on thin GaN template (∼2μm) with high dislocation density [low (109cm−2)] grown by metal-organic vapor-phase epitaxy (sample A) and the other on thick GaN template (∼20μm) with comparatively low dislocation density [high (108cm−2)] by hydride vapor-phase epitaxy (sample B). In order to understand the mechanism of leakage current in LEDs, the correlation between current-voltage characteristics and etch pit density of LEDs was studied.

In0.2Ga0.8N/In0.03Ga0.97N 3-period multiple quantum wells (MQWs) were grown by low pressure metalorganic chemical vapor deposition and the effects of pre-In flow prior to QW growth on its overall optical property were investigated. Pre-In flow did not change the structural property of the MQW structure such as In composition and period but strongly influenced its optical properties. MQW samples grown with pre-In flow exhibited longer peak wavelength and stronger peak intensity. CL measurement revealed more uniform and smaller emission centers in pre-In flow samples, implying a reduction of non-radiative defective regions and more In-rich regions. These results indicate that the In source introduced prior to QW growth preferentially gets incorporated around defect sites such as threading dislocations to inhibit their propagation while forming seeds for In-rich regions.

We investigated the effect of two-monolayer thick protection layers of GaN and AlGaN at the well growth temperature after the growth of InGaN well in InGaN/GaN MQW structures by MOCVD. The protection layers were very effective in inhibiting the re-evaporation of indium atoms regardless of the growth of GaN barriers at high temperature from TEM and PL. In addition, the use of GaN barrier grown at high temperature using GaN protection layers improved the emission efficiency due to the growth of high quality GaN without indium desorption. From the thermal treatment of as-grown samples, the redshift of emission was observed, which was ascribed to the increased quantum confined Stark effect by thermal stress, showing negligible indium gathering and atomic intermixing.

In order to understand the origin of leakage current, light emitting devices were grown on two different templates with apparently different dislocation density: one on thin GaN template (∼2 µm) with higher dislocation density (low × 10 9 cm -2 ) prepared by metal-organic vapor-phase epitaxy (sample A), and the other on thick GaN template (∼20 µm) with comparatively low dislocation density (high × 10 8 cm -2) by hydride vapor-phase epitaxy (sample B). Especially, the template B showed very low value of the dislocation density for a screw component, 2.2 × 10 7 cm -2 evaluated by transmission electron microscope and 2.3 × 10 7 cm -2 approximated by the Williamson-Hall plot which was evaluated by high resolution X-ray diffraction, respectively. On the other hand, sample A showed one order higher, low × 10 8 cm -2 , than that of sample B for a screw component. Sample A showed the larger leakage current (more than two orders of magnitude) than sample B in a forward-biased region and a reverse-biased region also. It is expected that the screw dislocation were strongly contributed to the leakage current of forward and reverse I-V regions in LEDs.