Processing And Characterization Of Advanced Algan Gan Heterojunction Effect Transistors

Download or read book Processing and Characterization of Advanced AlGaN/GaN Heterojunction Effect Transistors written by Jaesun Lee and published by . This book was released on 2006 with total page 176 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) have demonstrated high current levels, high breakdown voltages, and high frequency power performance due to its unique material properties. The further improvements of AlGaN/GaN HEMTs rely on the improvement of material quality and further reduction of parasitic resistance. The purpose of this study is to fabricate and characterize AlGaN/GaN HEMTs for high frequency and high power applications. The first focus of this research is to investigate the post-gate annealing effect on the direct current and radio frequency device performances. Post-gate annealing of AlGaN/GaN turns out to be one of the simple and effective techniques to improve breakdown voltage and power performance of devices dramatically. Especially, after post-annealing at 400 0C for 10 minutes, the maximum drain current at a gate bias of 1 V increases from 823 mA/mm to 956 mA/mm. The transconductance of the devices was improved from 223 mS/mm to 233 mS/mm. The breakdown voltages of the devices were enhanced remarkably from 25 V to 187 V. The threshold voltage exhibited a negative shift. The values fT and fMAX increase from 24 GHz and 80 GHz to 55 GHz and 150 GHz, respectively. The output power and associated gain at 10 GHz are improved from 16.4 dBm and 11.4 dB to 25.9 dBm and 19 dB, respectively. The power added efficiency (PAE) is improved from 29.4 to 52.5 %. The second focus is to develop self-aligned AlGaN/GaN HEMTs, which are very attractive because of the minimized source access resistance. However, the thick metal scheme and high processing temperature of ohmic contacts on III-nitrides hinder the realization of self-aligned devices. In this study, self-aligned AlGaN/GaN high electron mobility transistors are fabricated and characterized with the thin metal schemes of Ti/Al/Ti/Au and Mo/Al/Mo/Au for gate to source and drain self-alignment. Thin Mo/Al/Mo/Au metal layer show good ohmic contact behavior even after annealed for 5 minutes at 600 0C in a furnace while thin ohmic metal scheme of Ti/Al/Ti/Au does not produce ohmic contact even after annealed at 750 0C for 30 minutes. The third focus is to develop the enhancement mode AlGaN/GaN HEMTs. Quasi-enhancement mode AlGaN/GaN HEMT devices with 1-um gate length are fabricated. These quasi-enhancement mode devices exhibit the threshold voltage of as low as - 0.3 V, a gm of 140 mS/mm, an fT of 4.3 GHz, and an fMAX of 13.3 GHz, respectively. Further improvement of enhancement-mode GaN-based HEMT devices is desired for applications of complementary integrated circuits.