SEM and AFM characterisation of high-mesa patterned InP substrates prepared by wet etching

The aim of this study has been to optimise a reliable technological process that would be capable of producing quality mesa etches (40 μm high) into (100) SI InP substrates yielding well-defined smooth (211) faceted walls and (100) bottom etched planes. Such well-defined patterned substrates can serve for non-planar overgrowth experiments with the aim to create 2DEGs at tilted heterostructures and finally to design and manufacture novel magnetic-field sensors. Using xHCl:1H3PO4 solutions well-defined smooth (211)A surfaces were produced for 0.5<x<5. However, the (100) bottom etched surfaces were covered with etch pits which merged into an all-area mesh-like feature for deep etches. We also used 1HCl:yH3PO4:zCH3CH(OH)COOH solutions (y=2, 3 and 6 and z=0, 0.2, 0.4, 0.6, 0.8. and 1). The incorporation of lactic acid reduced the number and size of etch pits in the (100) etched surfaces, however it caused increased surface roughness at the (211)A and (100) etched planes for higher lactic acid volume ratios. We showed that the roughness can be sufficiently reduced by subsequent polishing in 2% Br2–MeOH.