Atomic Layer Deposition of Ga₂O₃ Films Using Trimethylgallium and Ozone

Abstract

In this manuscript, we demonstrate a new process for the atomic layer deposition (ALD) of gallium oxide (Ga2O3) thin films using trimethylgallium (TMGa) and ozone. We evaluated a variety of oxygen sources for Ga2O3 ALD using TMGa but found that only ozone was effective. We explored the mechanism for Ga2O3 ALD using in situ quartz crystal microbalance, Fourier transform infrared spectroscopy, and quadrupole mass spectrometry studies. We found that TMGa dissociatively adsorbs onto the Ga2O3 surface to form Ga(CH3)2 surface species and liberate ∼20% of the methyl ligands as CH4. Next, the ozone reacts with these methyl species to form hydroxyl and formate surface groups and liberate CH2O. We prepared ALD Ga2O3 films on Si(100) and fused SiO2 substrates and analyzed the films using a variety of techniques. We found the Ga2O3 growth to be self-limiting with a growth rate of ∼0.52 Å/cycle between 200 and 375 °C. Moreover, the Ga2O3 films were stoichiometric, free of residual carbon, and exhibited properties similar to bulk Ga2O3. Scanning electron microscopy revealed smooth films with good step coverage over trench structures, and X-ray diffraction showed that the films were amorphous as-deposited but crystallized to β-Ga2O3 upon annealing at 900 °C.

Atomic Layer Deposited Gallium Oxide Buffer Layer Enables 1.2 V Open‐Circuit Voltage in Cuprous Oxide Solar Cells

“…The film's optical bandgap is estimated by a linear extrapolation using the relation of , where α , h , and ν are the optical absorption coefficient, Planck constant, and photon frequency, respectively. The band gap of the Ga 2 O 3 film was estimated to be 5.18 eV, which is slightly larger than the values (4.9 – 5.0 eV) reported previously …”

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 .…”

“…Other synthesis methods include RF sputtering 23 , precipitation 24 , halide vapor phase epitaxy (HVPE) 25 and molecular beam epitaxy (MBE) 8 . Most Ga2O3 atomic layer deposition (ALD) papers using a variety of deposition temperatures, chemical precursors and substrates report deposition of amorphous material [26][27][28][29][30][31][32] . However, in a recent study we reported that α-Ga2O3 could be deposited by plasma enhanced ALD (PEALD) onto sapphire (α-Al2O3) substrates 33 .…”

Dopant activation in Sn-doped Ga2O3 investigated by X-ray absorption spectroscopy

“…4 In addition, aGa2O3:Sn thin films are deposited using ALD and PLD methods. The ALD film is deposited at 120 °C in a custom-built cylindrical reactor with a 30 cm long and 3 cm wide sample stage, and a chamber volume of 0.627 L. The Ga and Sn precursors used in the ALD process are bis(µ-dimethylamino)tetrakis(dimethylamino)digallium 6,10 and tetrakis(dimethylamido)tin(IV)…”