Using time‐resolved photoluminescence spectroscopy on GaInN/GaN multiple quantum well structures, we analyze the radiative and nonradiative processes contributing to the “green gap” in GaN‐based light emitting devices. We observe that it is only partly caused by a reduced oscillator strength due to the Quantum Confined Stark Effect (QCSE) which becomes stronger with increasing indium concentration and well width. As the dominant effect we observe a reduction of nonradiative lifetimes when the indium concentration is increased. For higher indium concentrations, we find an additional nonradiative recombination path that might be attributed to an increased generation of defects like misfit dislocations, nitrogen vacancies and/or indium clusters within the optically active region. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Via temperature‐dependent time‐resolved photoluminescence spectroscopy, we investigate the radiative and nonradiative recombination processes in thin (quantum well widths of about 1.5 nm) a‐plane, m‐plane, (11true2‾2) and (20true2‾1) GaInN/GaN fivefold quantum well structures of varying indium content grown on low defect density GaN substrates and GaN templates. At room temperature, we observe surprisingly short radiative lifetimes in the range from 100 ps to 1 ns for these structures, being about one to two orders of magnitude shorter than for similar c‐plane quantum wells. This large difference cannot solely be explained by the larger overlap matrix element in non‐ and semipolar wells. Higher exciton binding energies and lower effective density of states masses may contribute to an enhanced radiative probability. The nonradiative recombination exhibits a thermally activated behavior with activation energies of about 10 meV for (11true2‾2) and around 25 meV for nonpolar quantum wells. These values are lower than the quantum well barrier height and the exciton binding energy, but in a similar range as the localization energies estimated from the radiative recombination.

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We demonstrate a strong dependence of the indium incorporation efficiency on the strain state in m-oriented GaInN/GaN multi quantum well (MQW) structures. Insertion of a partially relaxed AlInN buffer layer opens up the opportunity to manipulate the strain situation in the MQW grown on top. By lattice-matching this AlInN layer to the c- or a-axis of the underlying GaN, relaxation towards larger a- or smaller c-lattice constants can be induced, respectively. This results in a modified template for the subsequent MQW growth. From X-ray diffraction and photoluminescence measurements, we derive significant effects on the In incorporation efficiency and In concentrations in the quantum well (QW) up to x = 38% without additional accumulation of strain energy in the QW region. This makes strain manipulation a very promising method for growth of high In-containing MQW structures for efficient, long wavelength light-emitting devices.

We report on the control of optical polarization properties of nonpolar m-plane Ga1–xInxN/GaN quantum wells by manipulation of anisotropic in-plane strain via the insertion of a partially relaxed AlInN interlayer prior to the quantum wells. Structures with different interlayer compositions are compared to m-plane quantum wells without interlayers as reference. With these interlayers, we are able to either decrease or increase the strain in the quantum wells, as well as change the strain in just one in-plane direction to further change the anisotropy of strain. This results in a modified valence band structure which strongly influences optical properties such as the degree of optical polarization. Systematic evaluation of the polarization splittings opens up the opportunity to experimentally determine the deformation potential D5 for different anisotropic strain states for indium contents between 13% and 37%, which provides a good estimate for D5 for InN. Finally, we compare the measurements to k ⋅ p calculations, using the deformation potential derived from the experiments.