Analysis and Modeling of Vertical Current Conduction and Breakdown Mechanisms in Semi-Insulating GaN Grown on GaN: Role of Deep Levels

• Published in: IEEE transactions on electron devices Vol. 68; no. 5; pp. 2365 - 2371
• Main Authors: Stoklas, Roman, Chvala, Ales, Sichman, Peter, Hasenohrl, Stanislav, Hascik, Stefan, Priesol, Juraj, Satka, Alexander, Kuzmik, Jan
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.05.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Breakdown; Carrier compensation; Conduction bands; Electric breakdown; Electric potential; electrical breakdown; Electron mobility; Electron traps; Gallium nitride; GaN; Potential barriers; semi-insulating (SI); simulation; space-charge-limited current (SCLC); Substrates; Temperature measurement; Transistors; Valence band; vertical transistor; Voltage
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2021.3065893

Vertical current conduction in a 1.3-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>-thick semi-insulating (SI) C-doped GaN grown on a GaN substrate is analyzed. During the growth, pressure was varied from 100 to 20 mbar in order to increase C concentration from <inline-formula> <tex-math notation="LaTeX">\sim 1\times 10^{{17}} </tex-math></inline-formula> cm −3 to <inline-formula> <tex-math notation="LaTeX">\sim 6\times 10^{{18}} </tex-math></inline-formula> cm −3 ; SI GaN is sandwiched between two n-GaN layers. Optical transitions suggest two acceptor levels: ~0.9 eV above the valence band and ~0.6 eV below the conduction band. Current-voltage characterizations reveal a space-charge-limited-current conduction with an impact-ionization-assisted filling of traps in a moderately C-doped sample. On the other hand, highly compensated SI GaN forms a ~0.5-eV potential barrier at the interface with n-GaN, whereas the breakdown voltage exceeds 350 V. As the model explains, deep acceptors above the valence band compensate residual donors and lead to an electron mobility collapse. On the other hand, depending on C concentration, acceptors below the conduction band play a different role. In the moderately doped SI GaN, they act as electron traps and define the breakdown voltage. On the other hand, acceptors below the conduction band in highly compensated SI GaN are responsible for the barrier-controlled conduction and reaching of the avalanche.