ALD Al2O3, SiNx, and SiON films as passivating coatings in AlGaN/GaN HEMT

The effect of passivating ALD Al₂O₃, SiN_x and SiON coatings of different thicknesses on the change in the charge and density of states of AlGaN/GaN heterostructures are studied. The electrophysical parameters of the structures were evaluated using C-V characteristics measured at different frequencies and I-V characteristics. Based on the considered zone diagrams of structures with different control voltages and the evaluation of the elemental composition of the films by Auger spectroscopy, it was shown that the cause of the formation of a large positive charge upon deposition of ALD Al₂O₃ and SiN_x films is the appearance of an additional piezoelectric charge in the AlGaN buffer layer. It is shown that the use of SiON films with an oxygen concentration of more than 3% does not lead to the formation of an additional positive charge, but can cause current fluctuations when measuring I-V characteristics. A possible mechanism of carrier transport in the SCR region, leading to such fluctuations, is considered.

AlGaN/GaN heterostructure, passivating coating, fixed charge, band diagram, spontaneous and piezoelectric polarization, donor-like centers, hopping conductivity, surface states

1. Chevtchenko S. A., Reshchikov M. A., Fan Q., Ni X., Moon Y. T., Baski A. A., Morkoç H. Study of SiNх and SiO2 passivation of GaN surfaces. J. Appl. Phys., 2007, vol. 101, no. 11, pp. 2740324. DOI: 10.1063/1.2740324

2. Mizue C., Hori Y., Miczek M., Hashizume T. Capacitance-voltage characteristics of Al2O3/AlGaN/GaN structures and state density distribution at Al2O3/AlGaN interface. Jpn. J. Appl. Phys., 2011, vol. 50, no. 2R, p. 021001. DOI: 10.1143/JJAP.50.021001

3. Matys M., Stoklas R., Blaho M., Adamowicz B. Origin of positive fixed charge at insulator/AlGaN interfaces and its control by AlGaN composition. J. Appl. Phys., 2017, vol. 110, no. 24, p. 243505. DOI: 10.1063/1.4986482

4. Geng K., Chen D., Zhou Q., Wang H. AlGaN/GaN MIS-HEMT with PECVD SiNx, SiON, SiO2 as gate dielectric and passivation layer. Electronics, 2018, vol. 7, no. 12, p. 416. DOI: 10.3390/electronics7120416

5. Matys M., Adamowicz B., Domanowska A., Michalewicz A., Stoklas R., Akazawa M., Yatabe Z., Hashizume T. On the origin of interface states at oxide/III-nitride heterojunction interfaces. J. Appl. Phys., 2016, vol. 120, no. 22, p. 225305. DOI: 10.1063/1.4971409

6. Shengyin Xie, Jiayun Yin, Sen Zhang, Bo Liu, Wei Zhou, Zhihong Feng. Trap behaviors in AlGaN–GaN heterostructures by C–V characterization. Solid-State Electronics, 2009, vol. 53, no. 11, p. 1183—1185. DOI: 10.1016/j.sse.2009.08.006

7. Zubkov V. I. Characterization of InxGa1-xAs/GaAs quantum-well heterostructures by C–V measurements: band offsets, quantum-confinement levels, and wave functions. Semiconductors, 2007, vol. 41, no. 3, pp. 320—326. DOI: 10.1134/S1063782607030153

8. Miczek M., Mizue C., Hashizume T., Adamowicz B. Effects of interface states and temperature on the C–V behavior of metal/insulator/AlGaN/GaN heterostructure capacitors. J. Appl. Phys., 2008, vol. 103, no. 10, p. 104510. DOI: 10.1063/1.2924334

9. Arulkumaran S., Egawa T., Ishikawa H., Jimbo T. Characterization of different –Al-content AlxGa1-xN/GaN heterostructures and high-electron-mobility transistors on sapphire. J. Vacuum Science & Techology B, 2003, vol. 21, no. 2, p. 888—894. DOI: 10.1116/1.1556398

10. Hashizume T., Hasegawa H. Effects of nitrogen deficiency on electronic properties of AlGaN surfaces subjected to thermal and plasma processes. Applied Surface Science, 2004, vol. 234, no. 1–4, pp. 387—394. DOI: 10.1016/j.apsusc.2004.05.091

11. Dinara S. M., Jana S. Kr., Ghosh S., Mukhopadhyay P., Kumar R., Chakraborty A., Bhattacharya S., Biswas D. Enhancement of two dimensional electron gas concentrations due to Si3N4 passivation on Al0.3Ga0.7N/GaN heterostructure: strain and interface capacitance analysis. AIP Advances, 2015, vol. 5, no. 4, p. 047136. DOI: 10.1063/1.4919098

12. Sameer J. J. Surface and mechanical stress effects in AlGaN/GaN high electron mobility transistors: Thesis: Ph. D. Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017, 161 p. URL: https://dspace.mit.edu/handle/1721.1/111325

13. Mosca R., Gombia E., Passaseo A., Tasco V., Peroni M., Romanini P. DLTS characterization of silicon nitride passivated AlGaN/GaN heterostructures. Superlattices and Microstructures, 2004, vol. 36, no. 4–6, pp. 425—433. DOI: 10.1016/j.spmi.2004.09.006

14. Hori Y., Mizue C., Hashizume T. Process conditions for improvement of electrical properties of Al2O3/n-GaN structures prepared by atomic layer deposition. Jpn. J. Appl. Phys., 2010, vol. 49, no. 8R, p. 080201. DOI: 10.1143/JJAP.49.080201

15. Hashizume T., Alekseev E., Pavlidis D., Boutros K. S., Redwing J. Capacitance-voltage characterization of AlN/GaN metal-insulator-semiconductor structures grown on sapphire substrate by metalorganic chemical vapor deposition. J. Appl. Phys., 2000, vol. 88, no. 4, p. 1983—1986. DOI: 10.1063/1.1303722

16. Eller B. S., Yang J., Nemanich R. J. Electronic surface and dielectric interface states on GaN and AlGaN. J. Vacuum Science & Technology A, 2013, vol. 31, no. 5, p. 050807. DOI: 10.1116/1.4807904

17. Dusza J., Steen M. Microhardness load/size effect in individual grains of a gas pressure sintered silicon nitride. J. Amer. Ceramic Society, 1998, vol. 81, no. 11, pp. 3022—3024.

18. Iakovleva N. I., Nikonov A. V., Boltar K. O., Sednev M. V. Analysis of current-voltage characteristics in UV AlGaN heterostructure FPAS. Uspekhi Prikladnoi Fiziki, 2018, vol. 6, no. 1, pp. 44—55. (In Russ.)

19. Monroe D. Hopping exponential band tails. Phys. Rev. Lett., 1985, vol. 54, no. 2, pp. 146—149. DOI: 10.1103/PhysRevLett.54.146

20. Bochkareva N. I., Voronenkov V. V., Gorbunov R. I., Shreter Y. G., Virko M. V., Kogotkov V. S., Leonidov A. A., Vorontsov-Velyaminov P. N., Sheremet I. A. Hopping conductivity and dielectric relaxation in Schottky barriers on GaN. Semiconductors. 2017. vol. 51, no. 9, pp. 1186—1193. DOI: 10.1134/S1063782617090068