Fabrication of Low-Threshold InGaAs/GaAs Ridge Waveguide Lasers by using in situ Monitored Reactive Ion Etching,

In general, fabrication of ridge waveguide lasers is simpler than that of other structures such as diffusion and buried heterostructure lasers. Either wet etching or dry etching processes are generally used for ridge formation. Since the height of the ridge determines the optical confinement as well as the surface recombination and lateral diffusion of the injected carriers, it is important to control the ridge formation properly to optimize the device performance. Recently, an in situ laser-monitored dry etching technique has been widely used in device processing, and various monitoring techniques have been developed to accomplish precise etching-depth control such as growing a stop-etch layer which makes a clear difference in the monitored signal. With the ability of accurate ridge etching, high performance ridge waveguide lasers are expected. However, the reported ridge lasers did not have the low threshold current predicted theoretically even though very good results were obtained for the material threshold current density and for buried heterostructure lasers. This was particularly true for strained-layer InGaAsGaAs structures.