Gallium nitride (GaN) transistors have gained significant importance in recent years due to their superior performance and potential for various applications. GaN is a compound semiconductor that could emerge as an alternative to silicon for high-power electronics and high-frequency applications. GaN based high electron mobility transistors (HEMTs) have several advantages over traditional silicon-based devices, making them attractive for a wide range of applications. GaN has a wide bandgap, high electron mobility, and the ability to withstand high electric fields, which translates into several benefits for transistor applications. These properties enable GaN transistors to operate at higher voltages, higher frequencies, and higher temperatures, compared to silicon-based devices. Additionally, GaN transistors exhibit lower on-resistance, resulting in reduced power losses and improved efficiency [1, 2]. The structural breakdown in high power GaN-on-GaN p-n diode devices due to stress has been reported [3]. Structural damage may also evolve in GaN crystals due to grinding and polishing processes. This paper reports GaN film grown on a silicon substrate that has been investigated for high electric field induced lattice damage via cameraless terahertz (T-ray) imaging. In addition, T-ray time-domain spectroscopy (TDS) has been conducted on the same GaN film as a function of depth via nondestructive and noncontact pump-probe technique. This is termed as the deep-level TDS. Further, a pair of GaN HEMT dies have been imaged at the channel area where the deep-level TDS has also been conducted. A pristine die has been compared with a similar die that was irradiated with mild nuclear radiation. The channel width measured via T-ray metrology of both dies matches those determined from the optical microscope images. However, T-ray deep-level spectral analysis of both dies reveal that the pristine die’s channel structure remains unaffected up to 5.5 THz up to a depth of 3 µm while that of the irradiated die’s channel structure’s performance reduced to 4.2 THz to the same depth of 3 µm. Details of data and analysis have been discussed. The technique may be deployed to other similar systems and devices.
Keywords. T-ray Volume Imaging, GaN Lattice Damage, GaN Film, GaN HEMT, T-ray Deep-level Spectroscopy, Radiation Treatment. REFERENCES [1] Meneghini, M., Meneghesso, G., & Zanoni, E. (2017). Power GaN devices: Materials, applications and reliability. Switzerland: Springer. https://doi.org/10.1007/978-3-319-43199-4. [2] Schimmel, S., Tomida, D., Ishiguro, T., Honda, Y., Chichibu, S. F., & Amano, H. (2023). Temperature field, flow field, and temporal fluctuations thereof in ammonothermal growth of bulk GaN—Transition from dissolution stage to growth stage conditions. Materials, 16(5), 2016. https://doi.org/10.3390/ma16052016. [3] Peri, P., Fu, K., Fu, H., Zhao, Y., & Smith, D. J. (2020). Structural breakdown in high power GaN-on-GaN p-n diode devices stressed to failure. Journal of Vacuum Science & Technology A, 38(6), 063402. https://doi.org/10.1116/6.0000488.
