Study on the anomalous ridge width effect in GaN-based blue-violet laser diodes caused by carbon contamination

To investigate the anomalous ridge width effect and its underlying physical mechanisms in GaN-based blue-violet laser diodes (LDs), four LDs with ridge widths of 4 µm, 6 µm, 8 µm, and 10 µm are fabricated. The power-current-voltage (P-I-V) characteristics show that the output power of the 6 µm-wide ridge LD is significantly higher than that of the 10 µm-wide ridge LD, contradicting the empirical expectation that increasing ridge width may enhance power output. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analyses confirm the presence of a carbon-rich protrusion beneath the ridge on the front cavity surface of the 10 µm-wide ridge LD, thereby significantly reducing the output power. Combined with process flow analysis, this carbon contamination is attributed to the cleaving and sputter deposition processes on the cavity facets. Due to the high optical absorption of carbon, the increased optical loss leads to the anomalous reduction in output power. This study reveals the microscopic physical mechanism underlying the abnormal ridge width effect, providing critical insights for process optimization in high-power LDs.