In this paper, we discusse the origin of basal-plane stacking faults (BSFs) generated in the homoepitaxial hydride vapor phase epitaxy (HVPE) growth of m-plane gallium nitride (GaN). We investigated ...the effects of seed quality, especially dislocation density, on BSF generation during homoepitaxy. The results clearly identify basal-plane dislocation in the seed as a cause of BSF generation. We realized high-quality m-plane GaN substrates with a 2-in. diameter using HVPE on low-dislocation-density m-plane seeds.
Defects in ammonothermal GaN have been studied using a monoenergetic positron beam. Through measurements of Doppler broadening spectra of the annihilation radiation, the major defect species was ...identified as a Ga vacancy coupled with impurities such as oxygen and/or hydrogen. Those defects were found to be stable even after annealing at 1000°C. The shape parameter S for the Doppler broadening spectrum corresponding to positron annihilation at the surface was found to be decreased by illumination within energy ranges of 1.5–2.6eV and 3.2–3.6eV. This phenomenon is attributed to the suppression of recombinations between holes and electrons due to trapping centers, which can hold electrons for a long time, and a resultant accumulation of holes at the surface. Recovery of the S value required almost one day, but it was shortened by the annealing at 1000°C.
•Vacancy-type defects in ammonothermal GaN were studied by positron annihilation.•The defect species was identified as a Ga-vacancy coupled with impurities.•Electron trapping centers were studied by positron annihilation with illumination.
InGaN single quantum wells (SQWs) grown on m-plane bulk GaN substrates show significant differences in peak emission wavelength when grown on substrates oriented nominally on-axis compared to ...substrates with small intentional misorientations (miscuts) towards the orthogonal −c-direction or a-direction. SQWs on substrates intentionally miscut toward the a-direction emit longer wavelengths than those with miscuts towards the −c-direction in a variety of identical growth conditions, while SQWs on nominally on-axis m-plane with pyramidal hillocks features display emission characteristics of both. These preliminary co-loaded growth studies may provide insight into broad or anomalous wavelength emission observed on nonpolar GaN-based visible light emitters and suggest opportunities for improving LED and laser diode device performance on this naturally occurring crystal plane.
•We examine emission characteristics of InGaN quantum wells on misoriented m-plane substrates.•Blue quantum wells on on-axis m-plane substrates show broad and dual wavelength emission and non-uniform in incorporation.•Substrates misoriented in the c- or a-direction lead to smoother film morphologies and more uniform quantum well emission.•Substrates misoriented in the a-direction show much higher In incorporation than other m-plane substrate orientations and longer emission wavelengths.
The first 30-mW-class semipolar blue light-emitting diode (LED) on a free-standing ($10\bar{1}\bar{1}$) GaN substrate has been demonstrated by using microscale periodic backside structures. The light ...extraction efficiency and corresponding output power were greatly enhanced, by up to 2.8-fold (bare chip) compare with conventional devices. At a driving current of 20 mA, the LED showed an output power of 31.1 mW and an external quantum efficiency of 54.7%. Semipolar GaN LED technology is now comparable to commercial $c$-plane blue LED technology, not only in terms of internal material properties but also in terms of chip processing techniques.
Dispersion relationships of the refractive index and extinction coefficient of m-plane Al1−xInxN epitaxial films (x = 0.00, 0.23, and 0.30) grown on a freestanding m-plane GaN substrate were ...determined by spectroscopic ellipsometry measurement. The experimentally obtained ellipsometric parameters tan Ψ and cos Δ, which represent the differences in the p- and s-polarized amplitudes and phases of the incident light, respectively, were well fitted using the standard analytical functions. As the measurement was carried out at photon energies between 1.55 and 5.40 eV, the dispersion curves of the extinction coefficient k exhibited local maxima at approximately the Al1−xInxN bandgap energies of x = 0.23 and 0.30, and the sample with x = 0.00 showed an ordinal absorption spectrum with a bandtail formed owing to high-concentration residual impurities. A large and x-dependent energy difference between the absorption and emission spectra (Stokes shift) was observed for the Al1−xInxN films, suggesting the presence of carrier localization phenomena.
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