Optimum Carbon Concentration in GaN-on-Silicon for Breakdown Enhancement in AlGaN/GaN HEMTs

• Published in: IEEE transactions on electron devices Vol. 67; no. 6; pp. 2311 - 2317
• Main Authors: Remesh, Nayana, Mohan, Nagaboopathy, Raghavan, Srinivasan, Muralidharan, Rangarajan, Nath, Digbijoy N.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Aluminum gallium nitrides; Breakdown; Buffers; Carbon; Carbon doping; Cathodoluminescence; Doping; Electric breakdown; Electric potential; Free energy; Gallium nitride; Gallium nitrides; GaN buffer; Heat of formation; HEMTs; High electron mobility transistors; high-electron mobility transistor (HEMT); lateral breakdown; leakage; Leakage current; MODFETs; Semiconductor devices; Statistical methods; Temperature dependence; Temperature measurement; Vacancies; Voltage
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2020.2989421

This article reports on the experimental and analytical determination of the optimum carbon concentration in GaN to achieve enhanced breakdown in AlGaN/GaN high-electron mobility transistors (HEMTs). The lateral breakdown voltage increases when carbon doping is increased from <inline-formula> <tex-math notation="LaTeX">3\times 10^{{18}} </tex-math></inline-formula> to 10 19 cm −3 beyond which it decreases, whereas there is no substantial enhancement in the vertical breakdown voltage with carbon doping. We invoke carrier statistics in a compensated semiconductor vis-à-vis the formation energy of carbon-occupying Ga (or N) vacancies to explain the observed buffer leakage. Temperature-dependent data indicate that the buffer leakage current is due to hopping transport, the activation energy of which yields the positions of the defect states within the bandgap. The increase in buffer leakage beyond optimum C concentration is attributed to the formation of shallow donor traps by carbon atoms occupying Ga vacancies (C Ga ). The observations correlated with the relative intensities of the defect-mediated peaks in the cathodoluminescence (CL) data of the samples. Based on our findings, a C doping beyond 10 19 cm −3 is not recommended for GaN buffers in order to achieve high breakdown voltages.