Low temperature growth of gallium oxide thin films via plasma enhanced atomic layer deposition

Abstract

Herein we describe an efficient low temperature (60-160 °C) plasma enhanced atomic layer deposition (PEALD) process for gallium oxide (GaO) thin films using hexakis(dimethylamido)digallium [Ga(NMe)] with oxygen (O) plasma on Si(100). The use of O plasma was found to have a significant improvement on the growth rate and deposition temperature when compared to former GaO processes. The process yielded the second highest growth rates (1.5 Å per cycle) in terms of GaO ALD and the lowest temperature to date for the ALD growth of GaO and typical ALD characteristics were determined. From in situ quartz crystal microbalance (QCM) studies and ex situ ellipsometry measurements, it was deduced that the process is initially substrate-inhibited. Complementary analytical techniques were employed to investigate the crystallinity (grazing-incidence X-ray diffraction), composition (Rutherford backscattering analysis/nuclear reaction analysis/X-ray photoelectron spectroscopy), morphology (X-ray reflectivity/atomic force microscopy) which revealed the formation of amorphous, homogeneous and nearly stoichiometric GaO thin films of high purity (carbon and nitrogen <2 at.%) under optimised process conditions. Tauc plots obtained via UV-Vis spectroscopy yielded a band gap of 4.9 eV and the transmittance values were more than 80%. Upon annealing at 1000 °C, the transformation to oxygen rich polycrystalline β-gallium oxide took place, which also resulted in the densification and roughening of the layer, accompanied by a slight reduction in the band gap. This work outlines a fast and efficient method for the low temperature ALD growth of GaO thin films and provides the means to deposit GaO upon thermally sensitive polymers like polyethylene terephthalate.

Epitaxial GaN using Ga(NMe2)3 and NH3 plasma by atomic layer deposition

“…Notably, all previous reports using 1 has resulted in amorphous films at all deposition temperatures. 19,21,22 We show that 1 displayed self-limiting behaviour in a temperature range from 130-250 1C on Si (100). Deposition of GaN on 4H-SiC(0001) rendered epitaxial films with near stochiometric composition and very low impurity levels of carbon and oxygen.…”

“…Tris(dimethylamido)gallium(III) dimer 1 has been previously used in ALD studies, [19][20][21] however its thermal properties have not been reported as far as we know. Thermogravimetric analysis (TGA) showed 1 evaporated in a single step from 140-230 1C, with only 5% of residual mass (Fig.…”

Low temperature growth and optical properties of α-Ga2O3 deposited on sapphire by plasma enhanced atomic layer deposition

“…However, several studies have also shown that the direct bandgap (located at Γ) is only 0.04 eV larger, with a bandgap of 4.88 eV [42][43][44] . The majority of papers available in which UV-Vis spectroscopy has been used for the study of Ga2O3 films use the direct bandgap assumption when calculating Tauc plots 1,4,26,28,30,32,45 , i.e: ℎ ∝ (ℎ − ) 1 2 ⁄ where is the optical absorption coefficient, ℎ is the photon energy and is the optical bandgap. Thus a plot of ( ℎ ) 2 against ℎ can be used to extract .…”

Epitaxial GaN using Ga(NMe2)3 and NH3 Plasma by Atomic Layer Deposition

“…Notably, all previous reports using 1 has resulted in amorphous films at all deposition temperatures. 19,21,22 We show that 1 displayed self-limiting behaviour in a temperature range from 130-250  C on Si(100). Deposition of GaN on 4H-SiC(0001) rendered epitaxial films with near stochiometric composition and very low impurity levels of carbon and oxygen.…”

“…Herein, we report low temperature deposition of GaN using tris(dimethylamido)gallium(III), (Ga(N(CH3)2)3 1, with NH3 plasma by ALD. Precursor 1 has been previously used for ALD of Ga2O3 19,20 and Ga2S3 21 and CVD of GaN 22 , but not for ALD of GaN. Notably, all previous reports using 1 has resulted in amorphous films at all deposition temperatures.…”