Fabrication of MnAs microstructures on image substrates and their electrical properties

We explore wet and dry etching processes of thin MnAs layers grown on GaAs(0 0 1) substrates for microstructuring. Most of the common wet chemical etch solutions for GaAs react with MnAs strongly and in a peculiar manner. Unidirectional cracks are generated when the MnAs layers are thicker than 100 nm. We demonstrate that the crack generation can be avoided by choosing a suitable etch solution or etch temperature. We fabricate submicrometer-wide MnAs wires using Ar ion milling. The resistivity of the narrow channels is measured over a temperature range covering the phase transitions in MnAs between the image, image, and image phases. The resistivity along the MnAs[0 0 0 1] direction is found to be smaller than that along the image direction regardless of the phase. A nearly linear temperature variation of the phase fraction is deduced in the image–image phase coexistence regime. The temperature coefficients of the resistivities are negative for the nonmagnetic phases.