| Project Detail |
Deep-levels induced by point defects (PDs) have always been a major challenge in semiconductor physics and technology as they usually degrade the performance of electronic and optoelectronic devices. However, in some cases, PDs exhibit an opposite character and can behave as quantum light emitter with unique properties. A prototypical system is the NV center in diamond that opened a new territory for physics and technology thanks to its amazing spin properties. In addition, PDs can also be stable single photon emitters (SPEs) at room temperature with promising perspectives for quantum communications.In this project we will investigate the two faces of PDs in III-nitride semiconductors. First, in work package 1 we aim at the systematic investigation of quantum point defects (QPDs) acting as SPEs up to room-temperature in the 500 to 750 nm and in the 1000 to 1600 nm spectral ranges in GaN and AlN semiconductors. The choice of these spectral ranges coincides with high-efficiency single photon detectors and optical fiber transparency windows. To reach this goal, we will adopt a strategy that cannot be easily implemented in other wide bandgap materials hosting QPDs, namely the ability to tune the position of the Fermi level (EF) through doping during growth. We will also make use of two different growth techniques: i) metal organic vapor phase epitaxy (MOVPE) which usually takes place at high temperatures (1000°C), i.e., close to thermodynamic equilibrium, and ii) molecular beam epitaxy (MBE) for which growth is performed at much lower temperatures (600-650°C). Hence, using MBE, the formation of defects might exceed the equilibrium value, which could promote the presence of rare QPDs not accessible via MOVPE. We will adopt a specific methodology to disentangle the role of structural defects on potential deep level formation. Finally, we will determine the impact of the EF position onto the properties of SPEs. Power-dependent and long time delay g(2) measurements will provide relevant information about the SPE behavior of the most promising QPDs. The second work package (WP2) is focused on the nonradiative character of PDs in the InGaN alloy. Nowadays, III-nitride semiconductors are mature and extensively used in white light emitting diodes (LEDs) for solid-state lighting purpose. Surprisingly, the physics of PDs in the InGaN/GaN quantum well (QW) active region of those devices is still barely understood even though they are the main source of nonradiative recombination. In addition, the carrier diffusion length is still debated while this parameter is crucial for the design and performance of next generation micro-LEDs with diameters less than 10 microns. In WP2, we thus aim at a better understanding of the nature of PDs in InGaN/GaN QWs and elucidating the origin of the surface defects created during high-temperature growth of the GaN buffer. The importance of strain will be investigated and the energy levels of PDs will be measured by deep level spectroscopy and their dependence on the InGaN bandgap should provide a key insight into their origin, i.e., group-III or group-V vacancies. PDs will be further studied at the microscale using time-resolved cathodoluminescence. This will give access to the intrinsic carrier diffusion length in defect-free area. These results will be interpreted in light of diffusion models in a disordered medium. This should provide new insight into the role of carrier localization in InGaN/GaN QWs. The understanding of carrier dynamics and the efficiency in high-indium content QWs is of prime importance for the development of long-wavelength InGaN based optoelectronics in general, and for microLEDs in particular. |
