Methods for Electrical and Electro-Optical Measurements on LEDs and Their Interpretation

Light-emitting diodes (LEDs) are widely used in many electronic devices, including lighting systems, indicators, and display panels. One of the newest developments in this field is the use of microLEDs, which are very small LEDs that can provide higher brightness, lower power consumption, and better image quality compared to traditional display technologies. These features make microLEDs promising for use in applications such as smart watches, augmented reality, and high-resolution screens. However, because of their small size, microLEDs can be more sensitive to small changes in design and fabrication. This means it is important to carefully measure how they perform in order to improve their quality and reliability. The main goal of this thesis is to develop and test a set of reliable and repeatable methods to measure the electrical and optical properties of microLEDs. These methods include current–voltage (I–V) measurements, optical power versus voltage (P–V) and emission spectra. A measurement system was built using a source-measure unit (SMU), an optical power meter, and a spectrometer. All instruments were controlled using LabVIEW, which made the measurements easier to automate and reduced the chance of human error. To test the measurement setup and methods, one commercial blue LED and two microLED samples were studied. The commercial LED was used as a reference to check that the system worked correctly. It showed a peak external quantum efficiency of 17%, as expected for high-quality devices. The two microLED samples gave lower EQE values, but the data still provided important information. For example, the results showed differences in leakage current, how efficiently the devices convert electrical energy into light, and how stable the emission was over a range of voltages. These results help explain what factors affect the performance of microLEDs, such as contact quality and internal losses. The methods developed in this work can be used in future research to compare different device designs and to improve how microLEDs are made.