Abstract
Gallium nitride (GaN) is the main component of modern-day high electron mobility transistors due to its favorable electronic properties. As electronic devices become smaller with more complex surface architecture, the ability to deposit high-quality GaN films at low temperatures is required. Herein, we report a new highly volatile Ga(III) triazenide precursor and demonstrate its ability to deposit high-quality epitaxial GaN by atomic layer deposition (ALD). This new Ga(III) triazenide, the first hexacoordinated Ga–N bonded precursor used in a vapor deposition process, was easily synthesized and purified by either sublimation or recrystallisation. Thermogravimetric analysis showed single-step volatilization with an onset temperature of 155 °C and negligible residual mass. Three temperature intervals with self-limiting growth were observed when depositing GaN films. The GaN films grown in the second growth interval at 350 °C were epitaxial on 4H–SiC without an AlN seed layer and found to have a near stoichiometric Ga/N ratio with very low levels of impurities. In addition, electron microstructure analysis showed a smooth film surface and a sharp interface between the substrate and film. The band gap of these films was 3.41 eV with the Fermi level at 1.90 eV, showing that the GaN films were unintentionally n-type-doped. This new triazenide precursor enables ALD of GaN for semiconductor applications and provides a new Ga(III) precursor for future deposition processes.
Highlights
Gallium nitride (GaN) is the key material in state-of-the-art AlGaN/GaN high electron mobility transistors used in highfrequency electronics
We report the synthesis, structure, and physical properties of tris(1,3-diisopropyltriazenide)gallium(III) 1, and demonstrate it as an excellent Atomic layer deposition (ALD) precursor for highquality epitaxial GaN thin films on 4H−SiC. This new Ga(III) precursor is the first example of a volatile hexacoordinated Ga−N bonded precursor used in a vapor deposition process and is shown to possess superior deposition chemistry for GaN over previously used tricoordinated literature precursors
The angular dispersion of the fast Fourier transform (FFT) patterns of this film is far less pronounced and implies a notably improved stacking coherence of the GaN crystal and is in contrast to our previously reported ALD of GaN with the Ga(NMe2)3.20 The X-ray diffraction (XRD) rocking curve (XRC) on the GaN film deposited at 350 °C showed the full width half maximum for the (0002) plane was 280 arcsec (0.07754°) (Figure S14)
Summary
Gallium nitride (GaN) is the key material in state-of-the-art AlGaN/GaN high electron mobility transistors used in highfrequency electronics. The C impurities incorporated in the films were expected, as the deposited surface species from metal amide precursors are known to suffer from low thermal stability.[21] Alternatively, bidentate ligands have been used in ALD precursor development to improve the thermal stability of a precursor as they provide two stronger chelating bonds to the metal center This has led to the formation of the homoleptic hexacoordinated Ga−N bonded Ga(III) amidinate (Ga(amd)3)[22] and guanidinate (Ga(guan)3)[23] compounds. We report the synthesis, structure, and physical properties of tris(1,3-diisopropyltriazenide)gallium(III) 1, and demonstrate it as an excellent ALD precursor for highquality epitaxial GaN thin films on 4H−SiC This new Ga(III) precursor is the first example of a volatile hexacoordinated Ga−N bonded precursor used in a vapor deposition process and is shown to possess superior deposition chemistry for GaN over previously used tricoordinated literature precursors
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