Temperature dependence of excitonic recombination in lateral epitaxially overgrown InGaN/GaN quantum wells studied with cathodoluminescence

Abstract

We have examined in detail the optical properties of InGaN quantum wells ͑QWs͒ grown on pyramidal GaN mesas prepared by lateral epitaxial overgrowth ͑LEO͒ in a metalorganic chemical vapor deposition system that resulted in QWs on ͕1-101͖ facets. The effects of In migration during growth on the resulting QW thickness and composition were examined with transmission electron microscopy ͑TEM͒ and various cathodoluminescence ͑CL͒ imaging techniques, including CL wavelength imaging and activation energy imaging. Spatial variations in the luminescence efficiency, QW interband transition energy, thermal activation energy, and exciton binding energy were probed at various temperatures. Cross-sectional TEM was used to examine thickness variations of the InGaN/GaN QW grown on a pyramidal mesa. CL imaging revealed a marked improvement in the homogeneity of CL emission of the LEO sample relative to a reference sample for a conventionally grown In 0.15 Ga 0.85 N/GaN QW. The characteristic phase separation that resulted in a spotty CL image profile and attendant carrier localization in the reference sample is significantly reduced in the LEO QW sample. Spatial variations in the QW transition energy, piezoelectric field, and thermal activation energy were modeled using excitonic binding and transition energy calculations based on a single-band, effective-mass theory using Airy function solutions. Band-edge and effective-mass parameters were first obtained from a strain-and In-composition-dependent k"p calculation for wurtzite In x Ga 1Ϫx N, using a 6ϫ6 k"p Hamiltonian in the ͕1-101͖ representations. The calculations and experiments confirm a facet-induced migration of In during growth, which results in a smooth compositional variation from xϷ0.10 at the bottom of the pyramid to x Ϸ0.19 at the top. We demonstrate the existence of a strong correlation between the observed thermal activation behavior of QW luminescence intensity and the associated exciton binding energy for various positions along the pyramidal InGaN/GaN QWs, suggesting exciton dissociation is responsible for the observed temperature dependence of the QW luminescence in the ϳ150 to 300 K range.

Semipolar GaN/GaInN LEDs with more than 1mW optical output power

“…To obtain such crystal planes on high-quality c-plane GaN, we start the epitaxial growth in the c-direction, followed by the selective growth of GaN stripes with triangular crosssection. Other crystal planes form on the stripe facets, on which finally the QW structures are grown [3][4][5]. Depending on the stripe orientation and the growth conditions, different crystal facets can be obtained which all possess reduced or even zero polarization fields.…”

The origins of double emission peaks in electroluminescence spectrum from InGaN/GaN MQW LED

“…There are several works reported on the light emission mechanism of the complicated system [12][13][14][15][16]. The emissions can be originated from the In-rich clusters and interface roughened multiple quantum wells (MQWs).…”

Influence of AlGaN/GaN/InGaN superlattice on the characteristics of LEDs grown by metalorganic chemical vapor deposition

“…The LEDs grown with the SLs showed a PL intensity that was approximately 2.6 times higher than that of the LEDs grown without the SLs. It was reported that a decrease in dislocation density tended to enable the strong carrier localization and enhanced efficiency of radiative recombination in InGaN/GaN MQWs [20][21][22]. It was also found that the PL intensity increased with decrease in strain in the quantum wells due to the reduced piezoelectric field [23].…”