Growth of gallium oxide thin films from gallium acetylacetonate by atomic layer epitaxy

Abstract

Gallium oxide thin films have been deposited by atomic layer epitaxy (ALE) using Ga(acac), (acac = pentane-2,4-dionate) and either water or ozone as precursors. Films were grown on silicon (loo), soda lime and Corning glass substrates. The influence of the deposition parameters (e.g. pulse duration, growth and source temperatures) on film growth were studied and by a proper choice of the parameters a self-controlled growth was demonstrated around 370 "C. Spectrophotometry, X-ray diffraction (XRD), Rutherford back-scattering spectroscopy (RBS) and X-ray photoelectron spectroscopy (XPS) were used to determine the refractive index, thickness, crystallinity and stoichiometry of the films. All the films were amorphous and highly uniform with only small thickness variations. The films deposited with water contained a considerable amount of carbon as an impurity whereas ozone as an oxidizer gave stoichiometric Ga203 films.Gallium oxide is a thermally and chemically stable material which is insulating at room temperature but semiconducting at higher temperatures. The n-type semiconducting property of gallium oxide is due to a slight oxygen deficit in the crystal lattice. Ga203 is the single stable oxidation state of gallium under normal conditions. It exists in several crystalline forms, of which the monoclinic, high temperature P-Ga203 modification is the most stable one. Because of its optical and electrical properties, gallium oxide has found applications in metal-insulator structures on GaAs' and facet coatings for GaAs-based lasers. Recently, the use of gallium oxide thin films as gas sensors has attracted increasing i n t e r e ~t . ~-~ At high temperatures (800-1000°C) the films can be used as oxygen sensors while at lower temperatures (<7OO"C) they can be used to make sensors for reducing gases.

Structural and Optical Characteristics of Gallium Oxide Thin Films Deposited by Ultrasonic Spray Pyrolysis

“…These deposition rate values (Ϸ30-60 A/min, depending on Ts͒ are higher than those obtained in gallium oxide films deposited by ALE using GAAc (Ϸ15 A/min), although the refractive index has similar values ͑1.8-1.9͒. 13 Although the deposition rate in the ALE process is lower than the value obtained in the present work, the refractive index values are still similar because film deposition in the ALE process was achieved by introducing the reactants alternately in the reactor using nitrogen as purging gas. Meanwhile in the present case the gallium source material ͑GAAc͒ and the oxidizer agent ͑water͒ were used, forming a liquid solution.…”

“…The carbon content in those films can be reduced to levels as low as 1 atom %, but only if ozone is used as the oxidizer agent. 13 Residual incorporated carbon is also observed in films prepared by chemical vapor deposition ͑CVD͒ using gallium trishexafluoroacetylacetonate as gallium source material. 11 A quantitative analysis of the Rutherford backscattering ͑RBS͒ spectra was made using the wellknown ''RUMP'' software.…”

ALD and MOCVD of Ga2O3 Thin Films Using the New Ga Precursor Dimethylgallium Isopropoxide, Me2GaOiPr

“…[36] Ga-doped zinc oxide (ZnO:Ga, GZO) is a wellknown n-type TCO material. [37] Thin films of gallium oxide have been prepared by various methods: (radiofrequency) magnetron sputter deposition, [1][2][3][4]6,7,9,10,12,25,27] electron beam evaporation, [15][16][17]21] pulsed laser deposition, [26,28,30,33,34,36] laser ablation, [31] CVD, [38][39][40][41][42][43][44][45][46][47] ALD, [48][49][50][51][52] molecular beam epitaxy, [32,35] vapor phase epitaxy, [53] spray pyrolysis, [54,55] and sol-gel process. [5,13,23,24] Among these methods, CVD is considered very important because it can readily be employed in industrial processes.…”

“…ALD is also important as the sizes of electronic devices become smaller. Precursors for gallium oxide thin films include Ga(hfac) 3 , [38,56] Ga(dpm) 3 , [56] Ga(acac) 3 , [48] Ga[OCH(CF 3 ) 2 ] 3 (HNMe 2 ), [39] [ [40] Ga(O i Pr) 3 , [41] GaCl 3 , [42] Me 3 Ga, [43][44][45]49] Ga 2 (NMe 2 ) 6 , [46,50] [Me 2 GaNMe 2 ], [51,52] Ga(ROCOCHOCOR) 3 , [47] Et 3 Ga, [53] [Me 2 GaOCH 2 CH 2 NMe 2 ] 2 , 57 etc. Except for the trialkylgallium compounds, the precursors are mostly solids at room temperature and not convenient to use, although some of them readily volatilize with mild heating.…”

Tuning the Thermal Properties of Hafnium Precursors by Tailoring the Ligands

“…In additional, this oxide material finds a range of potential applications such as optical fibers, sensors, thermal barrier coatings, waveguides etc. (1-3) Metal-organic chemical vapor deposition (MOCVD) (4), (5) and atomic layer deposition (ALD) (6), (7) are considered as the most attractive thin film deposition methods where large area uniformity, conformal coverage over complex topographies are required. One of the major challenges for a successful MOCVD or ALD process is the availability of suitable precursors exhibiting appropriate thermal and physical properties.…”