Micro-Photoluminescence (µ-PL)

Christian Mounir phD Thesis (2020)

The overall goal of our micro-photoluminescence (µ-PL) setup is to better understand LEDs (light emitting diodes), focusing on their efficiency, defect analysis and carrier diffusion. In general, µ-PL is a versatile technique to characterize and study the optical properties of materials on a smaller length scale. Our setup is illustrated in the image on the left side. In our research, we focus on the investigation of InGaN LEDs, which have emission wavelengths in the blue and green range. Photoluminescence is an emission of light from a semiconductor material that is triggered by excitation of the material's electronic system by incident photons. This means that a light source is required, which is used to excite the sample. In our setup, we have two different excitation lasers that are mainly used in cw mode, but also have pulsed modes of operation. The photons generated by PL contain important information about the electronic system of the material.
PL operation is generally easy and allows rapid sample changes, enabling many different devices to be measured. It is a non-destructive measurement mode and operates with local detection. We can achieve a very high spatial resolution that is near the diffraction limit. By placing the sample in a cryostat and using liquid helium, low temperature measurements down to 10K can be performed. Diffusion measurements, in which excitation and detection spots can be decoupled, are another possibility for investigation. In addition, it is possible to extend to time-resolved PL measurements, which can be used to analyze the temporal dynamics. This extension is accomplished by coupling the PL emission into a fiber, with which the emission reaches the streak camera setup and can thus be analyzed for its temporal properties.

mesurment example:

latest theses:
E. Reißig: Analyse des lateralen Transports von Ladungsträgern in der Umgebung von Defekten in InGaN Quantenfilmen mit Hilfe von mikro-Photolumineszenz Spektroskopie, Bachelorarbeit
C. Becht: Ortsaufgelöste Spektroskopie von Lokalisierung und Rekombination in InGaN Quantenfilmen, Masterabeit

latest publicationen:
C. Becht, et al. pss(b) (2023), "Diffusion Analysis of Charge Carriers in InGaN/GaN Heterostructures by Microphotoluminescence"