Perovskite semiconductors hold large promise for opto-electronic applications such as solar cells and light-emitting diodes (LEDs). In just a few years of research, perovskite LEDs have reached an external quantum efficiency of about 20%, almost at par with incumbent technologies.
By optical pumping, it has been established that the threshold power needed to observe amplified spontaneous emission and obtain lasing is as low as for other direct-bandgap semiconductors (such as III-V). Also in our labs, we routinely observe evidence of stimulated emission by optical pumping. Still, it has not been possible to reach lasing by electrical pumping in these systems. The goal of this PhD is to work towards this target.
We will investigate, design and fabricate specific light-emitting device structures that combine a high quantum efficiency by electrical pumping with ultra-low optical losses for waveguided photons. From the electrical point of view, the planned device structure will pump electrons and holes into the perovskite active layer without metal contacts in the vicinity of the active layer, such as to minimize photon losses. To that end, we plan to investigate the use of gated electron and hole transport layers. This structure would also allow to balance the electron injection current and the hole injection current for any level of current injection, which is important to keep a high radiative recombination efficiency in the active layer at high current densities (as needed to reach population inversion). Furthermore, we plan to use device geometries with ultra-low optical losses, for example ring resonator geometry.
The PhD student will design and model the structures from electrical and optical viewpoint, and subsequently fabricate them in our cleanrooms. He/she will characterize the realized structures electrically and optically to quantify the loss mechanisms. Several iterations of device concepts can be expected. Systematic measurements of the optical pumping threshold for lasing in devices that are driven electrically will quantify the gap to bridge towards reaching population inversion by electrical pumping, and from there reach injection lasing.
The candidate PhD student has a background in nano-science, nano-engineering, nano-technology and semiconductor (opto-electronic) devices and physics. He/she has a strong affinity for semiconductor technology and a keen interest in optical and electro-optical properties of materials. Experience with semiconductor lasers is a plus. The research will be supported and guided by several experts from different domains in imec. For the realization of low-loss waveguide structures, it is foreseen to use advanced photolithographic patterning in the imec cleanrooms. The project fits in the plan to make ultra-bright light emitting thin-film diodes and lasers, funded by the ERC Advanced Grant of promotor Paul Heremans.
Required background: Nano-science, Nano-technology, Semiconductor physics, Opto-electronics, Semiconductor technology; knowledge of optics is a plus
Type of work: 40% device work, 40% advanced electrical and optical characterization, 10% modeling and simulation, 10% literature study
Supervisor: Paul Heremans
Daily advisor: Robert Gehlhaar
The reference code for this position is 1812-97. Mention this reference code on your application form.