【Domestic Papers】Study of GaN Thick Films Grown on Different Nitridated Ga₂O₃ Films

      Researchers from the Nanjing University have published a dissertation titled "Study of GaN Thick Films Grown on Different Nitridated Ga₂O₃ Films" in Crystals.

Project Support

      This work is supported by Project supported by National Natural Science Foundation of China (No. 62404097), National Key R&D Program of China (2022YFB3605204, 2022YFB3605201) Fund from the Solid-State Lighting and Energy-Saving Electronics Collaborative Innovation Center and PAPD.

Background

      Gallium nitride (GaN), as one of the III-nitride semiconductor materials, has been widely studied for the preparation of high-performance optoelectronic and high-power electronic devices due to its wide bandgap, high electron mobility, and excellent physical properties. GaN-based light-emitting and photodetection devices cover the entire wavelength range from ultraviolet to visible, which plays an important role in the transmitting and receiving ends of optical wireless communication systems. Recently, GaN substrates with low threading dislocation density (less than 10⁴–10⁵ cm⁻²) and low residual strain have shown potential for use in the homoepitaxial growth of GaN-based devices and show promise to further enhance GaN-based device performance. However, the high price, small size, and inconsistent quality of free-standing GaN (FS-GaN) has limited its applications.

Abstract

      In this paper, various Ga₂O₃ films, including amorphous Ga₂O₃ films, β-Ga₂O₃, and α-Ga₂O₃ epitaxial films, have been nitridated and converted to single-crystalline GaN layers on the surface. Although the original Ga₂O₃ films are different, all the converted GaN layers exhibit the (002) preferred orientation and the porous morphologies. The ~200 µm GaN thick films have been grown on the nitridated Ga₂O₃ films using the halide vapor phase epitaxy (HVPE) method. Raman analysis indicates that all the HVPE-GaN films grown on nitridated Ga₂O₃ films are almost stress-free. An obvious GaN porous layer/Ga₂O₃ structure has been observed in the interface between GaN thick films and sapphire substrates. The porous GaN layers can be used as promising templates for the preparation of free-standing GaN substrates.

Conclusions

      In summary, the growth of stress-free GaN thick films on nitridated Ga₂O₃ films has been successfully performed using the HVPE method. Single crystalline GaN layers have been formed by the nitridation of the Ga₂O₃ films prepared by various methods under an NH₃ atmosphere. XRD and SEM results reveal that all the converted GaN layers exhibit an (002)-preferred orientation with porous morphologies. The correlation between Raman frequency shifts in the E₂ mode of the converted GaN layer was accurately quantified, revealing a stress of approximately 0.069 GPa. As-grown HVPE-GaN films are almost stress-free, with stronger photoluminescence (PL) intensity. These results suggest that Ga₂O₃ films for the preparation of porous GaN templates can be obtained by a simpler method with lower cost and better repeatability, which will be beneficial for the preparation of high-quality strain-released free-standing GaN substrates.