Plane GaN Templates Research Articles

Comparison study of N‐ and In‐polar {0001} InN layers grown by MOVPE

AbstractWe compare InN layers grown directly on c ‐plane (0001) sapphire and on (0001) GaN templates using metal‐organic vapor phase epitaxy. InN grown on nitridated c ‐plane sapphire showed N‐polarity, while InN grown on c ‐plane GaN templates showed In‐polarity. N‐polar and In‐polar InN layers showed different surface morphology and crystallinity. N‐polar InN was smoothest when grown at higher growth temperatures, while In‐polar InN was smoothest at intermediate growth temperatures. Growth mode of the N‐polar InN on sapphire is Frank‐Van der Merwe, while growth mode of the In‐polar InN on GaN templates is Volmer‐Weber. Electrical properties were similar for both layers. Lowtemperature photoluminescence of In‐polar InN layers is shifted to higher energies most likely due to biaxial compressive stresses. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carrier dynamics in non‐polar GaN/AlGaN quantum wells intersected by basal‐plane stacking faults

AbstractWe have investigated the recombination dynamics of carriers in non‐polar GaN/AlGaN quantum wells intersected by basal plane stacking faults and an a ‐plane GaN template layer. In the GaN template, both the photoluminescence decay and rise times measured across the basal plane stacking fault emission band increase with decreasing emission energy. This is consistent with a carrier transfer process from less localised to more deeply localised states within the basal plane stacking fault. However, in the quantum well structures this behaviour is suppressed due to the restriction in carrier transport imposed by the quantum wells. We also found that the decay time of the localised exciton emission in the quantum wells is dominated by a non radiative carrier transfer process involving the basal plane stacking faults. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Advances in InN epitaxy and its material control by MBE towards novel InN-based QWs

Initial stage of MBE-epitaxy processes of InN on c -plane GaN template and successful p-type doping were studied. It was found that InN epitaxy proceeds through SK-mode and 1-ML-thick InN can be coherently grown on GaN. Successful p-type doping of InN was achieved by Mg doping levels from 10 18 to about 3×10 19 cm −3 . Overdoped Mg's introduced new donors in InN resulting in n-type conduction. Novel structure InN-based QWs consisting of coherent 1-ML-thick InN wells embedded in GaN matrix were proposed and fabricated. It was confirmed that extremely fine structure InN QWs with quite sharp and flat hetero-interface were fabricated by self-limiting growth mode under In-polarity growth regime at remarkably higher growth temperatures up to 650 °C.

Improved quality nonpolar a ‐plane GaN/AlGaN UV LEDs grown with sidewall lateral epitaxial overgrowth (SLEO)

AbstractHigh quality nonpolar a ‐plane GaN templates were grown by utilizing sidewall lateral epitaxial overgrowth (SLEO) technique with threading dislocation density of ∼106–107 cm–2. 360 nm GaN/AlGaN multiple quantum well ultraviolet light emitting diodes were grown with metalorganic chemical vapor deposition. Reduced defect density SLEO a‐ plane, planar a ‐plane, and planar c ‐plane templates were co‐loaded for device growth and processed together in order to make relative device performance comparison. For SLEO a ‐plane LEDs E EL peak position was measured at 360 nm and it was independent of drive current. The linewidth of the emission was 7 nm. The series resistance of these diodes was as low as 16.5 Ω and the forward voltage was measured as 4.08 V at 20 mA. The external quantum efficiency of the high quality SLEO a ‐plane devices was ∼275× higher than planar a ‐plane devices. The highest output power was realized at 200 mA as 65 μW. The effect of contact geometry on electrical and optical characteristics of the devices was also discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characteristics of ultraviolet nonpolar InGaN/GaN light-emitting diodes using trench epitaxial lateral overgrowth technology

Abstract Ultraviolet nonpolar InGaN/GaN light-emitting diodes grown on trench epitaxial lateral overgrowth (TELOG) a -plane GaN template by metalorganic chemical vapor deposition were fabricated. Two emission peaks at 373 and 443 nm are observed from each fabricated device. The double emission peaks feature is identified by cathodoluminescence images, which show that the ultraviolet peak is emitted from the low-defect density wings on the TELOG and the blue peak is emitted from the TELOG-coalesced seed areas due to different incorporation of indium. The L–I–V diagram revealed that there are leakage current pathways due to the many threading dislocations in seed regions, and that the output power reached 0.2 mW at 140 mA. Two electroluminescence (EL) peaks are observed simultaneously when the driving current is below 50 mA. However, the EL peak at 373 nm dominates when current is above 50 mA. In addition, the degree of polarization of the ultraviolet peak was measured and found to be 28.7%.

Reduction in defect density over whole area of (1$ \bar 1 $00) m ‐plane GaN using one‐sidewall seeded epitaxial lateral overgrowth

AbstractWe succeeded in growing low‐defect‐density m ‐plane GaN on grooved m ‐plane GaN with SiO2 masks on the terrace region. By changing the V/III ratio, we were able to increase the growth rate of GaN on one sidewall, thereby achieving one‐sidedwall lateral growth. Dislocations and stacking faults were decreased markedly over the whole area. The densities of dislocations and stacking faults were 1.3 × 107 (cm–2) and <2.6 × 104 (cm–1), respectively. The photoluminescence intensity was 213 times higher than that of an m ‐plane GaN template on an m ‐plane 4H‐SiC substrate. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)