Two dimensionally patterned GaN_xA_{1- x} nanostructures were produced using ion implantation and pulsed laser melting followed by rapid thermal annealing. A systematic investigation of the band structure of the alloys and a nanoscale characterization of the designed band gap reduction were performed using ballistic electron emission microscopy (BEEM). The evolution of the nitrogen-concentration depth profile during the laser melting was found to be consistent with liquid-phase diffusion, solute trapping at the rapidly moving solidification front, and surface evaporation. The reduction of the Schottky barrier height of the Γ-like threshold at nitrogen compositions up to x = 0.016 was studied with BEEM and determined quantitatively using the second voltage derivative (SD) BEEM spectra to be -191 ± 63 meV per x = 0.01, which is close to the corresponding slope for samples grown by low-temperature molecular beam epitaxy. This slope is also consistent with the band gap narrowing measured on the same samples by photomodulated reflectance and is consistent with the band anti-crossing model for the splitting of the conduction band in GaN_xAs_1-x alloys. Lithographically patterned GaN_xAs _1-x dots were imaged by BEEM. Analysis of BEEM spectra of the locally confined dots indicates an alloying-induced decrease in the Schottky barrier height of four times the thermal energy at room temperature.