Anisotropic and smooth inductively coupled plasma etching of III-V laser waveguides using HBr-O2 chemistry

HBr inductively coupled plasma (ICP) etching is investigated to realize ridge laser waveguides on InP and GaAs substrates. It has been reported that pure HBr chemistry leads to undercut ridge profiles when a hard dielectric mask is used. In this paper we show that a passivation layer can build up on the sidewalls and prevent lateral etching at high ICP powers if a Si wafer is used as the sample tray. Ex situ energy-dispersive X-ray analysis coupled to transmission electron microscopy shows that the passivation layer is a Si-rich silicon oxide. Vertical sidewalls, a smooth etched surface, and a moderate etch rate compatible with the processing of shallow ridge lasers can be obtained for InP-based heterostructures. The optimized HBr etching process is used to etch InAs quantum dot shallow ridge lasers grown on InP(100) substrate and compared to a classical HCl selective chemical etch. The waveguide losses of the HBr-etched waveguide do not differ from those of the chemically etched waveguide by more than 1 cm(-1). Finally, we show that a similar passivation mechanism can be obtained during HBr ICP etching of GaAs/AlGaAs ridge waveguides, demonstrating that the same HBr (-O-2) chemistry is suitable for both GaAs and InP systems.