Nanocrystalline GaN and GaN: H films grown by RF-magnetron sputtering

Abstract

The structural and optical properties of nanocrystalline GaN and GaN:H films grown by RF-magnetron sputtering are focused here. The films were grown using a Ga target and a variety of deposition parameters (N 2 /H 2 /Arflow rates, RF power, and substrate temperatures). Si (100) and fused silica substrates were used at relatively low temperatures (T s ≤ 420K). The main effects resulting from the deposition parameters variations on the films properties were related to the presence of hydrogen in the plasma. The X-ray diffraction analysis indicates that the grain sizes (∼15nm) and the crystallized volume fraction significantly decrease when hydrogen is present in the plasma. The optical absorption experiments indicate that the hydrogenated films have absorption edges very similar to that of GaN single crystal films reported in the literature, while the non-hydrogenated samples present larger absorption tails encroaching into the gap energies.

The optical absorption edge of nanocrystalline Ga1−xMnxN films deposited by reactive sputtering

“…The absorption edges, calculated from the transmittance spectra, are shown in figure 2. The pure nc-GaN film presents a more abrupt increase of the absorption than the amorphous GaN (a-GaN) [21] but less steep than the monocrystalline one (c-GaN) [8,22], as we could expect from a nanophase material, which has many sources of electronic disorder such as lattice distortion and tension, wrong bonds and dangling bonds, which are present mainly in grain boundaries. This electronic disorder implies broadening of the valence and conducting bands and the appearance of a considerable density of tail states at the edges of these bands.…”

Structural, Morphological, Vibrational and Optical Properties of GaN Films Grown by Reactive Sputtering: The Effect of RF Power at Low Working Pressure Limit

“…The N 2 inlet pipe is directed to the substrate's surface, symmetrically positioned in relation to the vacuum outlet flange, as shown in Figure 1. This configuration provides a richer N 2 plasma, which has a beneficial effect to the sample crystalline quality 10,27 . A minimum Ar gas flow (adjusted from our preliminary experiments) was injected directly to the Ga target surface by an injection ring installed onto the magnetron shield.…”

Roles of Atomic Nitrogen/Hydrogen in GaN Film Growth by Chemically Assisted Sputtering with Dual Plasma Sources

“…Sputtering is not a major method for the growth of GaN, although it has an advantage of growth on large substrates at low temperature and low cost. − Crystalline GaN growth below 600 °C − has been achieved by reactive sputtering using a mixture of Ar and N 2 gases, despite contamination of polycrystalline phases. Additionally, a pulse sputtering deposition (PSD) method using Ga targets under ultrahigh vacuum (<10 –7 Pa) has been proposed to realize epitaxial growth by sputtering. , Precise time control of sputtering plasma has enabled the enhancement of Ga surface migration at temperatures below 760 °C.…”

“…Chemical reactions between additive gases and the grown surface should thus be controlled precisely to achieve a flat grown surface with high crystallinity. With regards to the reaction between H 2 and the GaN surface, conventional sputtering growth of GaN with H 2 degrades the grown GaN film due to the formation of hydrogen-related bonds with the host lattice atoms. , On the other hand, the promotion of molecular beam epitaxy (MBE) GaN growth with the addition of atomic hydrogen showed the possibility of crystalline control, even though the chemistry was not apparent . There is also a potential for chlorine plasma chemistry on the GaN surface to improve the film quality by controlling the etching effects of GaN.…”