Effects of substrate temperature, substrate orientation, and energetic atomic collisions on the structure of GaN films grown by reactive sputtering

Abstract

Growth stresses and cracking in GaN films on (111) The combined effects of substrate temperature, substrate orientation, and energetic particle impingement on the structure of GaN films grown by reactive radio-frequency magnetron sputtering are investigated. Monte-Carlo based simulations are employed to analyze the energies of the species generated in the plasma and colliding with the growing surface. Polycrystalline films grown at temperatures ranging from 500 to 1000 C clearly showed a dependence of orientation texture and surface morphology on substrate orientation (c-and a-plane sapphire) in which the (0001) GaN planes were parallel to the substrate surface. A large increase in interplanar spacing associated with the increase in both a-and c-parameters of the hexagonal lattice and a redshift of the optical bandgap were observed at substrate temperatures higher than 600 C. The results showed that the tensile stresses produced during the film's growth in high-temperature deposition ranges were much larger than the expected compressive stresses caused by the difference in the thermal expansion coefficients of the film and substrate in the cool-down process after the film growth. The best films were deposited at 500 C, 30 W and 600 C, 45 W, which corresponds to conditions where the out diffusion from the film is low. Under these conditions the benefits of the temperature increase because of the decrease in defect density are greater than the problems caused by the strongly strained lattice that occurr at higher temperatures. The results are useful to the analysis of the growth conditions of GaN films by reactive sputtering. V C 2013 AIP Publishing LLC.

Fast Growth of GaN Epilayers via Laser-Assisted Metal–Organic Chemical Vapor Deposition for Ultraviolet Photodetector Applications

“…22,25 The growth of high-quality GaN films suitable for device application were usually realized at high deposition temperatures. [31][32][33][34] In this study, we successfully demonstrated the fast growth of high-quality GaN epilayers on sapphire substrates with a growth rate of 25.8 µm/h using an optimized CO2 laser LMOCVD method. The growth of GaN epilayers followed previously documented two-step growth steps, 35 including a thin three dimensional (3D) GaN layer growth, lateral growth and coalescence of the 3D layer, and finally quasi-two dimensional (2D) growth at high temperatures.…”

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

“…Columnar growth without H 2 has often been reported for low-temperature sputtering growth at less than 600 °C with a single plasma source using Ar/N 2 mixture gases. 7 , 8 From the present growth results without H 2 , Ga migration was not promoted sufficiently, even with the dual source system at 600 °C, regardless of the N 2 flow rate. The separate supply of Ga and N can decrease the formation of intermediate products of Ga–N x on the target, although this effect did not directly contribute to enhance the migration of Ga on the growth surface.…”

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

“…Thus, it is expected that for 0.40 Pa the energetic particles are reaching the growing film surfaces with energy distribution very close to the original values as emerged from the target. These latter values, known to be 100, 20 and 20 eV for N and Ar, and Ga target-emitted atoms according to calculations performed by Schiaber et al 10 . On the other hand, for high pressures (1.33 and 2.67 Pa for example), the energetic particles originated from the target are expected to lose a significant fraction of their kinetic energy before reaching the substrates, probably going under 60, 4 and 3 eV (N and Ar, and Ga), obtained for 2.0 Pa and 50 mm distance used in 10 .…”

“…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.…”

“…The reactive sputtering technique is a simple and relatively low-cost technique for GaN film growth, allowing the use of low growth temperatures, high deposition rates, and is compatible with most substrates, in a wide range of sizes 8,9 . Temperatures below 600 ºC strongly favor a preferential growth of the crystalline axis c, that is, in the <0002> direction 10 . This is a great advantage since obtaining high-quality crystalline and electronic-grade GaN is almost always linked to the use of sapphire (Al 2 O 3 ) and/or silicon carbide (SiC) substrates, which are offered in small sizes and at extremely high prices.…”