Mounir Mensi

Optical absorption edge broadening in thick InGaN layers: Random alloy atomic disorder and growth mode induced fluctuations

To assess the impact of random alloying on the optical properties of the InGaN alloy, high-quality InxGa1−xN (0 < x < 0.18) epilayers grown on c-plane free-standing GaN substrates are characterized both structurally and optically. The thickness (25–100 nm) was adjusted to keep these layers pseudomorphically strained over the whole range of explored indium content as checked by x-ray diffraction measurements. The evolution of the low temperature optical absorption (OA) edge linewidth as a function of absorption energy, and hence the indium content, is analyzed in the framework of the random alloy model. The latter shows that the OA edge linewidth should not markedly increase above an indium content of 4%, varying from 17 meV to 30 meV for 20% indium. The experimental data initially follow the same trend with, however, a deviation from this model for indium contents exceeding only ∼2%. Complementary room temperature near-field photoluminescence measurements carried out using a scanning near-field optical mi...

Properties of near-field photoluminescence in green emitting single and multiple semipolar (202¯1) plane InGaN/GaN quantum wells

Scanning near-field photoluminescence (PL) spectroscopy has been applied to green emitting (202¯1) plane InGaN/GaN quantum well (QW) structures with 1, 5 and 10 wells to reveal the influence of the number of QWs on PL properties and their spatial variation. The data show no additional broadening or shift of the PL spectra related to the increase of the number of QWs. The QWs in the multiple QW structures are found to be nearly identical and the well width and/or alloy composition fluctuations uncorrelated. In spite that the thickness of the 10 QW structure is over the critical, no PL changes related to a structural relaxation have been detected.

Impact of alloy composition and well width fluctuations on linewidth broadening and carrier lifetimes in semipolar InGaN quantum wells (Conference Presentation)

Band potential fluctuations in InGaN/GaN quantum wells (QWs) induce carrier localization that affects emission linewidth and carrier recombination rate. Alloy composition and well width variations are considered as main sources of the potential fluctuations and are often treated indiscriminately. However, their impact on the emission linewidth and the carrier lifetimes may be different. Besides, the impact of the QW width fluctuations on the linewidth could possibly be reduced via optimization of growth, while random alloy composition fluctuations can hardly be avoided. In this work, we have studied these effects in green-emitting semipolar (20-21) plane InGaN/GaN single QW structures of different well widths (2, 4 and 6 nm) and in structures with different number of QWs (1, 5 and 10). Experiments have been performed by scanning near-field photoluminescence (PL) spectroscopy. It has been found that the well width fluctuations, compared to the InGaN alloy composition variations, play a negligible role in defining the PL linewidth. In multiple QW structures, the alloy composition fluctuations are spatially uncorrelated between the wells. Despite that the 10 QW structure exceeds the critical thickness, no PL linewidth changes related to a structural relaxation have been detected. On the other hand, the well width fluctuations have a large impact on the recombination times. In-plane electric fields, caused by the nonplanarity of QW interfaces, separate electrons and holes into different potential minima increasing the lifetimes in wide QWs.