GAAS FREESTANDING QUANTUM-SIZE WIRES

Ultrathin GaAs wires as thin as 15-40 nm and about 2 mum long have been grown on a GaAs substrate by metal-organic vapor-phase epitaxy. The wires, which consist of whiskers, are grown between 380 and 550-degrees-C using trimethylgallium and arsine (AsH3) as source materials. It is found that the wire growth direction is parallel to the [111] arsenic dangling-bond direction and can be perfectly controlled by the crystallographic orientation of the GaAs substrate surface. From transmission electron microscopic analysis it is revealed that the crystal structure of the wire coincides with the zinc-blende type for the growth temperature range of 460-500-degrees-C, but it changes to the wurtzite type at 420-degrees-C and temperatures higher than 500-degrees-C. It is also found that the wires have a twin-type structure around the [111] growth axis for zinc blende and [0001] growth axis for wurtzite. Photoluminescence study of these wires shows that the luminescence peak energy shifts to a higher energy as the wire width decreases from 100 to about 35 nm. In terms of luminescence polarization it is confirmed that the luminescence intensity parallel to the wires is four times greater than that perpendicular to the wires. These results clearly indicate the quantum-size effect of carriers confined in the wire. As a preliminary application to devices, a p-n junction has been formed along the GaAs wire. Light emission by current injection to the p-n junction wires has been observed in continuous operation at room temperature.