Our x-ray photoemission, magnetization, and transport studies on surface-etched and annealed (Ga,Mn)As epilayers elucidate the key role of the surface oxide in controlling the outdiffusion of self-compensating interstitial Mn impurities. We achieved a dramatic reduction in annealing times necessary to optimize the epilayers after growth and synthesized (Ga,Mn)As films with the Curie temperature reaching 180 K. A $p\text{−}n$ junction transistor is introduced, allowing for a large hole depletion in (Ga,Mn)As thin films at a few volts. The surface oxide etching procedure is applied to controllably reduce the thickness of the (Ga,Mn)As layer in the transistor and we observe a further strong enhancement of the field-effect on the channel resistance. The utility of our all-semiconductor ferromagnetic field-effect transistor in spintronic research is demonstrated on the measured large field effect on the anisotropic magnetoresistance.

• Received 22 February 2008

DOI:https://doi.org/10.1103/PhysRevB.78.054403