Design and performance of an electron cyclotron resonance plasma source for standard molecular beam epitaxy equipment

Abstract

An electron cyclotron resonance plasma source which can be inserted into a 2.25-in.-diam. sleeve designed for standard molecular beam epitaxy effusion cells has been designed and commissioned. This source uses a coaxial microwave line structure, with an external tuner and small electromagnets for the production of the resonance and extraction magnetic fields. It also provides the same source-to-substrate distance as other sources which eliminates wall collisions and resulting recombination of active species. The source exhibits stable and continuous operation over four decades of pressure and gridless plasma beam extraction. The low-pressure characteristics of the plasma beam for nitrogen (hydrogen) include an ion current density of 0.2 (1.0) mA/cm2, an ion density of 4×109 (5×1010) cm−3, an electron temperature of 120 000 (70 000) K over a 3-in. wafer located 20 cm from the source. This source has been successfully used to grow thin films of GaN and AlN and layered structures of these two materials on SiC and sapphire substrates at temperatures as low as 400 °C.