Direct observation of radio-frequency negative differential resistance in GaN-based single drift region IMPATT diodes

• Published in: Applied physics letters 2024-04, Vol.124 (17)
• Main Authors: Zhu, Zhongtao, Cao, Lina, Jönsson, Adam, Xu, Pengcheng, Xie, Jinqiao, Fay, Patrick
• Format: Article
• Language: English
• Subjects: Avalanche diodes; Bias; Electrical measurement; Gallium nitrides; Ionization coefficients; Leakage current; Parameters; Positive temperature coefficient; Radio frequency; Temperature effects; Transit time
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/5.0202565

We report the direct observation of radio-frequency negative differential resistance, via on-wafer S-parameter measurements, in GaN-based impact ionization avalanche transit time (IMPATT) diodes. Clear signatures of reflection gain are observed from 18.7 to 30.6 GHz. These observations have been made possible by suppressing the reverse leakage current (and thereby parasitic shunt conductance) by optimization of the fabrication process, in conjunction with the use of pulsed measurements to suppress device self-heating. Consistent with avalanche-dominated behavior, the measured DC reverse bias current–voltage measurements show a positive temperature coefficient of breakdown. For the high-frequency on-wafer characterization, pulsed-bias S-parameter measurements with low (0.0067%) duty cycle were used to mitigate thermal effects. The measured avalanche frequency aligns closely with theoretical predictions based on Gilden and Hines' small signal model [Gilden and Hines, IEEE Trans. Electron Devices ED-13(1), 169–175 (1966)], measured impact ionization coefficients [Cao et al., Appl. Phys. Lett. 112(26), 262103 (2018)], and experimental saturation velocity measurements [Bajaj et al., Appl. Phys. Lett. 107(15), 153504 (2015)]; this excellent agreement confirms IMPATT operation and provides insights needed to further optimize device performance.