Compositional and structural studies of amorphous GaN grown by ion-assisted deposition

Abstract

Amorphous GaN films have been deposited onto various substrates by ion-assisted deposition. The films were deposited at room temperature using nitrogen ion energies in the range 40-900 eV. Rutherford backscattering spectroscopy and nuclear reaction analysis show that the Ga:N atomic ratio is approximately one for films grown with ion energy near 500 eV; these films have the highest transparency. Films grown with ion energies below 300 eV are Ga rich, and show reduced transparency across the visible. Raman spectroscopy, x-ray diffraction, and transmission electron microscopy confirm the amorphous nature of the films. Annealing studies on a-GaN establish that the films begin to crystallise at a temperature of about 700°C. To investigate the local bonding environment of the Ga or N atoms, we have measured the extended x-ray absorption fine structure (EXAFS) of the transparent GaN films. The EXAFS results indicate that the films are dominated by heteropolar tetrahedral bonding, with a low density of homopolar bonds.

Deposition of Amorphous GaN by Compound Source Molecular Beam Epitaxy for Electroluminescent Devices

“…GaN-based materials on glass substrates are advantageous for use as light-emitting devices due to their low cost and large-area fabrication [1][2][3][4]. A lowtemperature process, which includes GaN growth or deposition, is required for the combination with other parts of light-emitting devices, such as electrodes.…”

Evolution of the local structure in GaN:O thin films grown by ion‐assisted deposition with film thickness

“…This layered arrangement can be deduced also by comparison of TEY (surface sensitivity) and transmission (bulk sensitivity) x-ray absorption results. In a previous transmission EXAFS experiment carried out on a 1000 nm thick film deposited onto Mylar, 13 the height of the jF R j peak corresponding to the second shell was onethird of the height of wGaN measured in transmission mode, whereas the first shell showed almost the same intensity for both samples. In TEY, the height of the second jF R j peak for the thickest film (¾450 nm) is half that of the reference sample.…”

“…Both the ion energy and flux have been optimized to achieve a Ga : N ratio within 10% of unity. 13 All the films used in this work were prepared using 500 eV N ions and a flux of a few times that of the Ga atoms. The film grows on the surface of the substrate at a rate of ¾0.5Å s 1 .…”

“…Long-range structural properties of some of these films also have been studied by resonant Raman spectroscopy, x-ray diffraction (XRD), TEM and electron diffraction. 13,16,39 Thin films (¾140 nm) are amorphous, whereas films above ¾400 nm thick give diffraction peaks of a width indicating nanocrystallites of ¾3 nm. The local structures around N atoms of two films 140 and 400 nm thick were characterized by x-ray absorption near the nitrogen K-edge.…”

“…15,16,40 Results have showed that a film 150 nm thick is amorphous and has significant amounts of trapped molecular nitrogen, whereas local crystalline order is higher and the amount of N 2 is lower in a 400 nm thick film. In a preliminary study, x-ray absorption spectra at the Ga K-edge in transmission mode were recorded also on a thicker film (¾1000 nm) deposited onto Mylar, 13 from which data it was concluded that IAD GaN films are predominantly heteropolar bonded with a local tetrahedral configuration. Defects consist of 5-20% of oxygen and some molecular N 2 , but to …”