Composition dependence of Schottky barrier heights and bandgap energies of GaN_xAs_1-x synthesized by ion implantation and pulsed-laser melting

Abstract

We present a systematic investigation on the band structure of the GaN_xAs_1-x alloys synthesized using nitrogen ion implantation followed by pulsed-laser melting and rapid thermal annealing. The evolution of the nitrogen-concentration depth profile is 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 composition up to x=0.016 is studied by ballistic electron emission microscopy (BEEM) and determined quantitatively using the second voltage derivative 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 bandgap narrowing measured on the same samples by photomodulated reflectance and is consistent with the band anticrossing model for the splitting of the conduction band in the GaN_xAs_1-x alloys. Lithographically patterned GaN_xAs_1-x dots are 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.