Low Temperature Plasma-Assisted Atomic Layer Epitaxy of III-V Nitride Semiconductors

The III-V nitride semiconductor family has been recognized as important for various device applications. Over the last 20-25 years, significant research attention has lead to successful technologies, especially in the area of light emitters which exploit the direct, tunable bandgap of these materials. Technologies based on electric polarization, piezoelectricity, and high breakdown field properties involve more-complex structures growth.  Such structures begin to challenge the abilities of conventional growth approaches.  In this seminar, I present the synthesis of III-nitride semiconductors by atomic layer epitaxy (ALE) where we find growth temperatures for high-quality crystalline layers are less than half of those needed for conventional growth methods.

Atomic layer deposition (ALD) is a pulsed growth method in which the precursors for growth are introduced in a sequence of gas pulses on top of an inert carrier gas flow.  ALE is simply ALD at temperatures that are sufficient to promote surface diffusion processes that allow either homo- or hetero-epitaxial growth. With proper surface preparations, high quality, wurtzitic AlN is grown at 500 °C [1].  These thin films (~36 nm) demonstrated smooth surfaces (~0.7 nm rms roughness for 10x10 mm² scan area) and a (0002) peak rocking curve of width 670 arc-sec. Similar results are demonstrated for GaN films grown between 350 and 450°C.  For InN, two growth regimes were defined.  One between 175 and 185°C, in which a new cubic phase of InN was realized, and a second regime between 220 and 260°C for which quality wurtzitic materials were grown [2].  Finally, III-V nitride ternaries (InAlN, InGaN and AlGaN) were grown over a wide stoichiometric range including the range where phase separation has been an issue for molecular beam epitaxy and chemical vapor deposition [3]. These ALE ternary layers were used to synthesize III-V nitride based device structures on GaN and demonstrated 2DEG at the interface.  These early results suggest great potential for ALE growth of III-N semiconductors, which can be used to design and grow different novel materials.