  Self assembled AlGaN polarization-induced nanowire light emitting diodes
(PINLEDs) with Gd-doped AlN active regions are prepared by plasma-assisted
molecular beam epitaxy on Si substrates. Atomically sharp electroluminescence
(EL) from Gd intra-f-shell electronic transitions at 313 nm and 318 nm are
observed under forward biases above 5V. The intensity of the Gd 4f EL scales
linearly with current density and increases at lower temperature. The low
electric field excitation of Gd 4f EL in PINLEDs is contrasted with high field
excitation in Gd:AlGaN MIS nanowire devices (metal/Gd:AlN/polarization induced
n-AlGaN) where it is concluded that PINLED devices offer over a three fold
enhancement in 4f EL intensity at a given device bias.
