Conductive surface oxide on CrN(001) layers

Epitaxial CrN(001) layers that are exposed to an O-2-containing atmosphere exhibit a conductive 2D surface oxide with a sheet conductance Gs,oxide = 5.9 x 10(-5) [Omega/rectangle](-1). This is demonstrated using in situ transport measurements in a 90% Ar-10% O-2 mixture with continuously increasing pressure from < 10(-6) to 240 Pa, showing a conductance increase that is independent of the CrN thickness d = 10 and 300 nm but is absent for control samples that are capped with insulating AlN prior to oxygen exposure. This suggests n-type doping of semiconducting CrN through substitutional replacement of N surface atoms with O. Cooling to 77 K leads to a decrease in Gs, oxide to 3.9 x 10(-5) [Omega/rectangle](-1), indicating that the conduction electrons are not fully delocalized. The overall results indicate a path towards 2D electron transport devices in refractory transition metal nitrides and may explain the large variation in previously reported transport properties of CrN.