Molecular beam epitaxy III-nitride growth for polarization sensitive devices based on M-plane films with in situ real time analysis by spectroscopic ellipsometry

摘要

Nonpolar oriented III nitrides have recently attracted considerable interest, owing to the absence of spontaneous and piezoelectric polarization and resulting electrostatic fields in heterostructures, which can be detrimental to the optoelectronic device efficiency. In this article, the authors present a study on the growth of M-plane GaN epilayers on LiAlO_2 substrates under Ga rich conditions and Ga stable conditions by plasma-assisted molecular beam epitaxy coupled with in situ spectroscopic ellipsometry. Previous studies on M-plane materials have suggested that optimum growth conditions with respect to surface morphology are those giving rise to a Ga trilayer coverage at low growth temperatures. By studying Ga adsorption/desorption in vacuum and in the presence of active nitrogen, we find that the total coverage for M-plane material is distinctly different for these two conditions. Under vacuum, the stable Ga coverage was 0.48 nm, while under N plasma, a thicker Ga stable coverage of 0.7 nm was determined. Using GaN layers grown at these conditions as buffer layers, M-plane InGaN layers were grown and processed into photodetectors exhibiting a polarization sensitive response.