Fabrication and characterization of a regrown InP/GaInAs quantum point contact

We demonstrate observation of quantized conductance of a regrown 90 nm wide quantum point contact (QPC) in InP/Ga_0.25In_0.75As at 10 K. The QPC is produced using high-resolution electron beam lithography and wet chemical etching to define the structure. PMMA was used as an etch mask during wet etching in HCl:CH₃COOH:H₂O₂ solution at 15°C. Proximity effect due to mask exposure by backward scattered electrons decreases masking property of PMMA. To overcome a problem of insufficient masking ability of the resist, a post-development hard baking above the glass transition temperature (Tg) of PMMA was performed. Using this simple approach, we were able to produce the QPCs as small as 50 nm in width