Supersieci na zrelaksowanych, porowatych podłożach GaN dla wydajnych czerwonych mikroLEDów o stabilnej długości fali emisji

The main objective of this project is to explore and develop a new generation of micro-LED (μLED) structures capable of emitting in the long-wavelength region (above 570nm) with the strong potential for achieving the red part of the visible spectrum. μLEDs are expected to combine high brightness, efficiency, fast switching, and small size. They are ideal for biomedical, sensing and display applications. Red μLEDs are gaining a lot of attention due to their potential applications in optogenetics, neural interfaces, and phototherapies thanks to deep tissue penetration. Red μLEDs also serve as precise light sources in sensors and lab-on-chip systems and are explored for high-speed VLC and Li-Fi or RGB displays. At present, red InGaN μLEDs face several key challenges. Achieving red emission requires high indium content, which induces significant strain and leads to crystal defects that reduce material quality and efficiency. This strain relaxation causes dislocations that decrease carrier lifetime and quantum efficiency, resulting in increased non-radiative recombination and lower brightness. To address these challenges and promote higher indium incorporation, significant research has focused on reducing compressive strain. The most promising approach (among the others) is the use of porous pseudo-substrates, which allows for elastic relaxation. This relaxation not only reduces strain but also leads to fewer defects that decrease emission efficiency. In order to solve these problems, we propose an innovative approach by using InGaN/InGaN superlattices (SLs) with different geometries in active region, grown on precisely engineered porous pseudo-substrates. By carefully selecting the widths of quantum wells (QWs) and quantum barriers (QBs), together with the design of customized porous substrates, we aim to enable higher indium incorporation, reduce internal strain and achieve highly efficient optoelectronic devices. The active region will consists of a set of InxGa1-xN/InyGa1-yN SLs with various geometries and with extremely narrow QWs of 0.5-2nm, variable indium content x>0.16 and with a quantum barriers (QBs) width of 0.75-5nm and y<0.1. To reduce strain we propose the use of porous pseudo-substrates. Project implementation consists in performing the following tasks: • Optimization of optoelectronic properties through simulations of test structures (LEDs) with an active region based on SLs. Initial structure optimization-WP1. • Preparation and optimalization of pseudo-substrates with porous GaN layers-WP2; • Epitaxy and processing of LED test structures and μLEDs with SLs as an active region with different geometries. Optimization of growth conditions-WP3. Quantum structures investigated in this project will be grown by plasma assisted molecular beam epitaxy (PA-MBE) technique on high quality GaN substrates. Porous pseudo-substrates will be produced by ECE technique with different porosification levels. Structural analyses will be performed by transmission electron microscopy (TEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). Optical properties including emission energies, spectral width, internal fields, and piezoelectric effects will be studied through photo- and cathodoluminescence under varying temperatures, excitation laser powers, and hydrostatic pressures. Electrical properties of the LEDs will be examined by L-I and U-I measurements. Additionally, theoretical investigations of the structures will be conducted, with electronic and optical properties calculated via ab initio methods and simulated using commercial software. Nitride SLs remain an innovative and relatively unexplored class of quantum structures. To the best of our knowledge, there are no published reports on the use of nitride SLs (as active region) grown on porous pseudo-substrates for longwavelength μLEDs. The novel approach proposed in this project combining engineered active region architectures with specially designed pseudo-substrates is aimed at meeting the specific requirements for μLED applications. Achieving emission at long wavelengths will serve as a proof of concept, particularly demonstrating the feasibility of using shortperiod SLs in next-generation red emitting μLEDs. This work will provide a new and valuable contribution to the current state of the art in light-emitting technologies and may also advance fundamental research in semiconductor based optoelectronics.