Fabrication of GaMnAs Magnetic Semiconductor Nanodot Arrays*

Ordered arrays of GaMnAs ferromagnetic semiconductor nanodots were fabricated using anodic porous alumina templates as etch masks. In this study we used nanochannel porous alumina membranes as masks for thermal evaporation coupled with reactive ion etching for the fabrication of organized hexagonal arrays of both manganese doped semiconductor and metal alloy comprised nanodots. The GaMnAs nanodots have diameters $\sim $40nm and dot periodicity of $\sim $80 nm. Field-cooled and zero-field-cooled magnetization measurements demonstrate that the dots are superparamagnetic at room temperature with a blocking temperature of T=30 K, below which they are ferromagnetic. This illustrates that arrays of uniform and highly-ordered nanodots can be fabricated inexpensively, rapidly and over large length scales for semiconductors which cannot be formed by techniques of self-assembly.