The role of liquid phase epitaxy during growth of AlGaN by MBE

We propose that the growth of III-Nitride semiconductors by plasma-assisted MBE under Ga-rich conditions takes place though the saturation of the liquid Ga covering the surface of the growing film with nitrogen, alloy constituents (aluminum and indium) and impurities. Thus, the proposed growth mode is a liquid phase epitaxy (LPE) rather than physical vapor phase epitaxy. While in traditional LPE growth the driving force is the gradient between the liquid and seed, in the proposed mode of MBE growth of nitrides the driving force is the concentration gradient due to the constant supply of active nitrogen, alloy components and impurities. The proposed LPE growth mechanism explains the relative temperature stability of GaN growth, the efficient doping with silicon and magnesium, and the selective desorption of oxygen and other impurities. Finally, the proposed LPE growth model can also account for the introduction of band structure potential fluctuations in AlGaN alloys, which improves their emission properties and leads to efficient deep UV-LEDs. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim