Nitrogen Source for Molecular Beam Epitaxy by Photofragmentation of Ammonia

Epitaxial growth of the aluminum gallium nitride (AlGaN) material system by molecular beam epitaxy (MBE) has been hindered by the lack of a suitable nitrogen source. The deposition of AlGaN at typical MBE growth temperatures results in nitrogen deficient films that suffer from low growth rates and high n-type background carrier concentrations. This problem has recently been addressed in MBE by increasing the reactivity of nitrogen containing precursors by creating plasmas or ion beams. Some success has been achieved using nitrogen containing plasmas generated by electron cyclotron resonance (ECR), although routine production of device quality material has yet to be realized and growth rates remain low (0.1 - 0.2 microns/hr) due to insufficient fluxes of the nitrogen species. We propose a new nitrogen source for MBE based on the efficient photolysis of ammonia (NH (sub 3)) by 193 nm excimer laser irradiation. The photogenerated NH (sub 2) radicals, chemically reactive and possessing higher sticking coefficients, should enhance nitrogen incorporation, increase growth rates, and allow lower growth temperatures in the deposition of nitride based films. The principal investigators have collaborated at North Carolina State University in the growth of silicon and III-V semiconductors. We will use our extensive experience in the areas of metalorganic molecular beam epitaxy (MOMBE) and laser assisted chemical vapor deposition (LCVD) to develop an effective nitrogen source for MBE.