Phone: þ1-807-3438311, Fax: 1 201 839 4341InN thin films were grown by a new technique, migration enhanced afterglow (MEAglow), a chemical vapour deposition (CVD) form of migration enhanced epitaxy (MEE). Here we describe the apparatus used for this form of film deposition, which includes a scalable hollow cathode nitrogen plasma source. Initial film growth results for InN are also presented including atomic force microscopy (AFM) images that indicate step flow growth with samples having root mean square (RMS) surface roughness of as little as 0.103 nm in some circumstances for film growth on sapphire substrates. X-ray diffraction (XRD) results are also provided for samples with a full width half maximum (FWHM) of the (0002) v-2u peak of as little as 290 arcsec. Low pressure conditions that can result in damage to the InN during growth are described.1 Introduction We report on the initial results for indium nitride films grown by a new technique that we have coined migration enhanced afterglow (MEAglow) deposition. Traditionally in RF plasma MBE systems, for the migration enhanced epitaxy (MEE) of group III metal nitrides, the metal is deposited as a thin wetting layer on a substrate and is subsequently nitrided using a nitrogen plasma to form a thin nitride semiconductor layer. A number of cycles of metal deposition with subsequent nitriding are used to build up a thicker film. Past thought has limited the thickness of the metal layer used for each cycle because deposition of more than a couple of monolayers of metal at a time can result in the formation of metal droplets on the substrate surface. It was believed that the nitridation of metal droplets would be difficult at best. However, recently it has been shown that even with these droplets being present good quality InN film growth can be achieved using thick metal deposition in a process that may be similar in some respects to liquid phase epitaxy (LPE) [1].For the work presented here we have migrated these recent MEE results to a low pressure chemical vapour deposition (CVD) environment for the deposition of InN. A nitrogen plasma is also used in this situation, however the

It is shown that attractive electrostatic interactions between regions of positive charge in RF plasmas and the negative charge of metal wetting layers, present during compound semiconductor film growth, can have a greater influence than substrate temperature on film morphology. Using GaN and InN film growth as examples, the DC field component of a remote RF plasma is demonstrated to electrostatically affect metal wetting layers to the point of actually determining the mode of film growth. Examples of enhanced self-seeded nanopillar growth are provided in the case where the substrate is directly exposed to the DC field generated by the plasma. In another case, we show that electrostatic shielding of the DC field from the substrate can result in the growth of Ga-face GaN layers from gallium metal wetting layers at 490 C with root-mean-square roughness values as low as 0.6 nm. This study has been carried out using a migration enhanced deposition technique with pulsed delivery of the metal precursor allowing the identification of metal wetting layers versus metal droplets as a function of the quantity of metal source delivered per cycle. It is also shown that electrostatic interactions with the plasma can affect metal rich growth limits, causing metal droplet formation for lower metal flux than would otherwise occur. Accordingly, film growth rates can be increased when shielding the substrate from the positive charge region of the plasma. For the example shown here, growth rates were more than doubled using a shielding grid.

Some initial results are presented for gallium nitride and indium nitride thin films grown on c‐plane sapphire using a prototype migration enhanced afterglow (MEAglow) system. Smooth surfaces of less than 1 nm root mean square surface roughness have been achieved for both InN and GaN films at growth temperatures of 450‐560 °C and 665 °C respectively. This result is attributed to the increased adatom diffusion length allowed for the metal species during the growth process. Thicker GaN layers can now be grown than those previously reported. For InN, an impressive full width half maximum value of 290 arcsec has been achieved for the (0002) reflection using ω−2θ X‐ray diffraction scans. Greater progress has so far been achieved for the growth of InN films because of the relative ease with which thick layers of indium metal can be nitrided to form a good quality layer. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Recent designs have allowed hollow cathode gas plasma sources to be adopted for use in plasma-enhanced atomic layer deposition with the benefit of lower oxygen contamination for non-oxide films (a brief review of this is provided). From a design perspective, the cathode metal is of particular interest since—for a given set of conditions—the metal work function should determine the density of electron emission that drives the hollow cathode effect. However, we found that relatively rapid surface modification of the metal cathodes in the first hour or more of operation has a stronger influence. Langmuir probe measurements and hollow cathode electrical characteristics were used to study nitrogen and oxygen plasma surface modification of aluminum and stainless-steel hollow cathodes. It was found that the nitridation and oxidation of these metal cathodes resulted in higher plasma densities, in some cases by more than an order of magnitude, and a wider range of pressure operation. Moreover, it was initially thought that the use of aluminum cathodes would not be practical for gas plasma applications, as aluminum is extremely soft and susceptible to sputtering; however, it was found that oxide and nitride modification of the surface could protect the cathodes from such problems, possibly making them viable.

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