  We demonstrate the electrical and optical control of ferromagnetism in
semiconductor heterostructures at high temperatures of 100-117 K. The
heterostructures consist of Mn delta-doped GaAs and p-type AlGaAs, where the
overlap of the hole wavefunction with the Mn delta-doping profile leads to high
ferromagnetic transition temperature TC of over 100 K (max. 172 K). We are able
to isothermally change the paramagnetic state to the ferromagnetic state and
vice versa, by applying a gate electric-field or by light irradiation. The
large modulation of TC (DTC ~15 K) at high temperatures (> ~100 K) demonstrated
here may pave the way to functional device applications compatible with the
present semiconductor technology.
