In-situ characterization of MOVPE growth dynamics and of diffusion mechanisms in nitrides and their influence on optoelectronic properties of InGaN/AlGaN/GaN quantum structures
Synthesis and Properties of Functional Materials
Final Report Abstract
In the Project, we have examined the InGaN/GaN Multiple Quantum Wells (MQWs) used to fabricate LEDs and laser diodes (LDs) emitting in the blue and green spectral region. The motivation of the Project was to advance our knowledge on two important hightemperature induced phenomena occurring in the InGaN MQWs during p-type growth of GaN above them: homogenization and decomposition. Both phenomena are related to the diffusion of point defects (i.e. gallium and nitrogen vacancies) from the layers below the MQWs (i.e. underlayer). The research objectives consisted of two steps: A) growth of the samples using Metalorganic Chemical Vapor Phase Epitaxy (MOVPE) at different growth conditions, including the post-growth annealing in the MOVPE reactor, and the ex-situ characterization using X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Photoluminescence (PL), B) In-situ structure characterization by X-ray measurements with synchrotron radiation during growth respectively annealing by use of a dedicated chamber developed for insitu X-ray diffraction and grazing incidence scattering methods with synchrotron radiation at the KIT Light Source and ex-situ sophisticated three dimensional reciprocal space maps (3D-RSMs) with synchrotron radiation. In the first step, our partner of the IHPP found out that heavy doping using Si or Mg in the Quantum Barriers (QBs) prevents decomposition (it was observed at much higher temperatures than for the undoped samples). In the next step, the influence of doping on decomposition of the QWs dependently on doping in the surrounding layers was investigated. Layers below and above QWs were doped with Si or Mg atoms. It was found that QWs surrounded by layers doped with Mg decomposed less compared to QWs surrounded by layers doped with Si. This was associated with a significant decrease in point defects mobility by forming clusters and complexes of vacancies by Mg dopants. The above results were described in two papers. In the second step, for the first time in-situ XRD measurements with synchrotron radiation at the NANO beamline at the KIT Light Source have been performed to study structural changes in the InGaN MQWs at temperatures up to 1000oC. We examined sample series, which each have the MQWs grown at identical conditions but with different underlayer material. We varied: i) the dislocation density (10^8 cm-2 vs 10^6 cm-2) by using sapphire and GaN as substrates, ii) the doping (Si, Mg, or undoped), iii) the growth temperature (790°C vs 930°C), iv) the chemical composition (InGaN vs GaN). The increase of dislocations decreased the indium content (χIn) in InGaN, the emission wavelength, and its intensity. Contrary to Mg-doping, Indium content enhanced the luminosity. The in-situ measurements allowed us to learn about the structural changes in the InGaN MQWs during heating and cooling processes. Taking benefit from the high brightness of the synchrotron X-ray beam from the superconducting 15 mm period undulator at NANO, we perform advanced reciprocal space mapping (RSM), providing reliable data to study temperature-induced microstructural changes. At temperatures up to about 940oC, we observed homogenization, above 940oC we observed decomposition of QWs. Complementary ex-situ TEM measurement of thermally treated QWs revealed trapezoidal objects with an amorphous phase and InGaN precipitates with a very high Indium content χIn. We also observed the influence of dislocations and doping on InGaN both phenomena. The in-situ measurements have deepened our understanding on InGaN homogenization and decomposition and on the strain state of layers in dependence of the underlayer below the MQWs.
Publications
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Improving thermal stability of InGaN quantum wells by doping of GaN barrier layers. Journal of Alloys and Compounds, 900, 163519.
Lachowski, Artur; Grzanka, Ewa; Grzanka, Szymon; Czernecki, Robert; Grabowski, Mikołaj; Hrytsak, Roman; Nowak, Grzegorz; Leszczyński, Mike & Smalc-Koziorowska, Julita
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Effect of doping of layers surrounding GaN/InGaN multiple quantum wells on their thermal stability. Materials Science in Semiconductor Processing, 166, 107752.
Lachowski, Artur; Grzanka, Ewa; Czernecki, Robert; Grabowski, Mikołaj; Grzanka, Szymon; Leszczyński, Mike & Smalc-Koziorowska, Julita
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In Situ X-Ray Study During Thermal Cycle Treatment Combined with Complementary Ex Situ Investigation of InGaN Quantum Wells. Nanomaterials, 15(2), 140.
Grzanka, Ewa; Bauer, Sondes; Lachowski, Artur; Grzanka, Szymon; Czernecki, Robert; So, Byeongchan; Baumbach, Tilo & Leszczyński, Mike
