X-Band AlGaN/GaN HEMT with Output Power over 20 W/mm and PAE over 50% using High Purity GaN Channel

An AlGaN/GaN high electron mobility transistor (HEMT) is still attractive devices for high frequency amplifier applications due to excellent properties of nitride materials like a wide band gap and large breakdown field. In the recent years, several reports concerning the high output power characteristics of AlGaN/GaN HEMT for X-band applications have been published [1,2]. Practical devices are required to satisfy not only high output but also power saving performance by high efficiency. In this work, we report on our success in simultaneously achieving a power density of more than 20 W/mm and an efficiency of more than 50% in the X-band.<br/>A high-performance X-band AlGaN/GaN HEMT were grown by metal-organic chemical vapor deposition (MOCVD) on a SiC substrate. The devices exhibited a peak transconductance (Gm) of 335 mS/mm and high maximum drain current of 1.34 A/mm. The load-pull measurements performed at 8 GHz corresponding to the target device operating frequency in X-band for devices with gate lengths of 0.25 μm demonstrated a peak power added efficiency (PAE) of 52.6% and a maximum output power density of 21.2 W/mm at 60 V. To the best of our knowledge this is the highest power ever reported for X-band AlGaN/GaN HEMT at Vds = 60 V. We achieved these results by improvement of the current collapse (dc-RF dispersion) in terms of optimizing the growth conditions of the GaN channel on top of the Fe-doped GaN buffer in AlGaN/AlN/GaN heterostructures. In particular, we investigated the impact of growth parameters of the GaN channel layer, such as the growth rate, and V/III ratio on the AlGaN/AlN/GaN HEMT performance. We found that the GaN channel layers grown with the high V/III ratio (about 5000) lead to a suppression of the current collapse in AlGaN/AlN/GaN HEMTs. Based on the photoluminescence (PL) measurements, we attributed the current collapse suppression to the reduction of GaN channel acceptor-like traps related to the carbon impurities. More precisely, for the GaN channel layers grown with the V/III ratio of about 5000, we observed a significant decreases of yellow luminescence from the AlGaN/AlN/GaN heterostructure, which directly correlated with the current collapse improvement. We believe that the achieved progress represents an important step toward the development of high power AlGaN/GaN HEMTs.<br/><br/>References<br/>[1] J. Kotani et al., "24.4 W/mm X-Band GaN HEMTs on AlN Substrates With the LPCVD-Grown High-Breakdown-Field SiNx Layer," in IEEE Journal of the Electron Devices Society, vol. 11, pp. 101-106, 2023,<br/>[2] K. M. Bothe et al., "Improved X-Band Performance and Reliability of a GaN HEMT With Sunken Source Connected Field Plate Design," in IEEE Electron Device Letters, vol. 43, no. 3, pp. 354-357, March 2022,