A Noncontact Photoelectric Joint Detection Method for Mini-LEDs Based on the Photovoltaic Effect

Miniaturization of light-emitting diodes (LEDs) has led to difficulties in characterizing photoelectric characteristics when using the conventional direct contact probe method, which risks damage to the small electrodes of LEDs, or the noncontact photoluminescence method, which can result in errors for known good die (KGD) detection. In this work, based on the photovoltaic effect and electromagnetic coupling theory, we propose a noncontact photoelectric joint detection method, which is realized via the use of a laser-excited photogenerated current in a closed loop and a differential-induced signal detected by a lock-in amplifier. This method can be used to derive critical photoelectric properties of miniaturized LEDs, especially the I-V relationship, the reverse saturation current, and the enhanced KGD detection. In addition, we find that the main sources of error in the detection system and evaluation of the reverse saturation current are the operating frequency of the system and the data measured using the lock-in amplifier. By testing a series of green mini-LED samples, the experimental results are found to be consistent with the theoretical analysis, substantiating the feasibility of the proposed noncontact method.