GaN-based violet lasers grown on sapphire with a novel facet fabrication method

Smooth and vertical facets for InGaN/GaN double heterostructure lasers grown on sapphire substrate are formed via a two-step method of dry etching and wet chemical etching. This two-step process consists of an inductively coupled plasma (ICP) etching with Ni metal as an etching mask to define the cavity length of the laser bars, followed by crystallographic wet etching in AZ400K developer to reduce the roughness and improve verticality of the sidewall. Optimization of ICP etching processes included the gas flow rate of Cl₂/Ar and the radiofrequency (RF) power to obtain a heavily striated facet angle of 3° from vertical. Combined with the wet etching processes, the facets along 〈112̅̅0〉 direction became smooth and vertical due to the preferentially etching feature of AZ400K in exposing the (101̅0) and other (101̅n)-type planes because of their slow etch rates compared with the other planes. To confirm the feasibility of the two-step etching facets, optically pumping experiment was carried out on InGaN/GaN double heterostructure lasers. Lasing behaviors of longitudinal mode peaked at 375 nm with a narrow line width of 1.3 nm was demonstrated on the laser using this two-step etching process, and proved it an effective way for laser facets fabrication method.