Low temperature processed CO₂ laser-assisted RF-sputtered GaN thin film for wide bandgap semiconductors

Figures & data

Table 1. Deposition methods, substrates, and corresponding substrate temperatures.

Type	Deposition method		Substrate	Substrate Temperature (°C)	Phase
Chemical vapor deposition	Metalorganic chemical vapor deposition		c-plane sapphire	500	Polycrystalline^[8^]
				1000	Single crystal^[20^]
	Hydride vapor phase epitaxy		c-plane sapphire	600	Polycrystalline^[9,10^]
				1000-	Single crystal^[19^]
Physical vapor deposition	Pulsed laser deposition		c-plane sapphire	700	Polycrystalline^[11,12^]
	Molecular beam epitaxy		c-plane sapphire	600	Polycrystalline^[13^]
				750	Single crystal^[20^]
	RF magnetron sputtering	Liquid Ga target	Quartz, c-plane sapphire	860	Polycrystalline^[17,18^]
		GaAs target	Quartz	850	Polycrystalline^[15,16^]
		GaN target	Glass	200–300	Amorphous^[14^]

Figure 1. Schematic of the CO₂ laser-assisted RF sputtering system.

Figure 2. X-ray diffraction patterns of the RF-sputtered GaN thin films deposited on sapphire substrates at the temperature of 200°C, RF power of 200 W, and working pressure of 15 mTorr, with different Ar partial pressure conditions (a) – (d) and without thin-film fabrication process (e).

Figure 3. X-ray diffraction patterns of the RF-sputtered GaN thin films deposited on sapphire substrates at the temperature of 200°C, working pressure of 15 mTorr, with different RF power conditions (a) – (c) and without thin-film fabrication process (d).

Figure 4. X-ray diffraction patterns of the CO₂-laser-assisted RF-sputtered GaN thin films deposited on a sapphire substrate by varying the energy density of the CO₂ laser. Process conditions: Ar partial pressure 60%, RF power 200 W, working pressure 15 mTorr, and substrate temperature 200°C (a) – (e). GaN thin film without CO₂ laser assistance (f) and without thin-film fabrication process (g).

Table 2. Surface energy of the (0001), (1120), (1011), and (1010) planes of GaN wurtzite.

GaN plane	(0001)	(1120)	(1011)	(1010)
Surface energy (J/m^2)^[22^]	2.64	1.53	1.76	1.40

Figure 5. X-ray diffraction pattern peak ratios in (0002), (1010) and (1011) orientations of CO₂ laser-assisted RF sputtered GaN thin films fabricated at different laser energy densities.

Figure 6. Transmittance and Tauc plot of the CO₂ laser-assisted RF-sputtered GaN thin films fabricated at different laser energy densities. The insert shows the simulated bandgaps of the GaN thin films from the transmittance values.

Figure 7. Bandgaps of the CO₂ laser-assisted RF-sputtered GaN thin films fabricated at different laser energy densities.

Figure 8. Scanning electron microscopy (SEM) images of the CO₂ laser-assisted RF-sputtered GaN thin films fabricated at different laser energy densities.

Figure 9. Scanning electron microscopy (SEM) surface images (a)-(e), cross-sectional images (f) of CO₂ laser-assisted RF sputtered GaN thin films fabricated at a laser energy density of 0.98 W/mm².

Figure 10. High-resolution scanning electron microscopy (SEM) images of the CO₂ laser-assisted RF sputtered GaN thin films fabricated at different laser energy densities.

Figure 11. Photoluminescence (PL) wavelength of the CO₂ laser-assisted RF-sputtered GaN thin films fabricated at different laser energy densities.

Figure 12. X-ray photoelectron spectroscopy (XPS) spectra of the Ga 3d core level of the CO₂ laser-assisted RF-sputtered GaN thin films deposited on a sapphire substrate by varying the energy density of the CO₂ laser. Process conditions: Ar partial pressure 60%, RF power 200 W, working pressure 15 mTorr, substrate temperature 200°C.

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