XIIth Semiconducting and Insulating Materials Conference, June 30 - July 5, Smolenice Castle, Slovakia
LT (Al)GaAs AND Al(Ga)As OXIDES FOR ELECTRONIC APPLICATIONS
J. CHAMPLAIN, C. ZHENG, and U. MISHRA
Electrical and Computer Engineering Department, University of California,
Santa Barbara, CA, 93116, USA
Low-temperature (LT) grown materials, such as LT GaAs and LT AlxGa1xAs, have seen numerous applications from gate insulators to terahertz antennas.1-5 In this paper, we present our research involving LT AlxGa1xAs applied in various fashions for electronic applications.
Our initial research into the area of low-temperature grown materials involved using LT AlxGa1-xAs as a surface passivant for high-power GaAs metal-semiconductor field-effect transistors (MESFETs). Most passivation schemes used today only provide for environmental passivation, protection against the environment and oxidation, but in general offer poor electrical passivation. We found that MESFETs fabricated with properly grown LT AlxGa1-xAs passivation layers displayed increased gate-drain breakdown voltages as well as reduced 1/f noise characteristics, therefore supplying excellent electrical passivation.
We next became involved in the fabrication and study of devices containing oxides formed from the wet oxidation of AlxGa1xAs; specifically FETs with an oxide as a buffer, underneath the channel, in order to suppress any substrate leakage. The so termed GaAs-On-Insulator (GOI) technology produced MESFETs with reduced subthreshold leakage currents and increased power-added-efficiencies (PAEs). The one detrimental feature of the technology, at the time, was the greatly reduced charge density in the channel of the devices after oxidation; believed to be due to excess arsenic that introduces interface states at the oxide/semiconductor interface.
The work of Reese et al. involving LT AlxGa1-xAs and the oxidation of AlxGa1-xAs suggests that the low-temperature grown material possibly assists in the removal of oxidation byproducts (mostly arsenic) increasing the oxidation rate.6 Incorporating LT AlxGa1-xAs buffers into GOI MESFETs resulted in devices, again with decreased subthreshold currents and increasead PAEs, but also with reduced charge lost in the channel due to oxidation. These devices produced record PAEs for GaAs MESFETs.7
Our current research involves the continued study of oxides for electronic applications, specifically incorporating the GOI technology with pseudomorphic high-electron mobility transistors (pHEMTs) for high efficiency and power and oxide aperture heterojunction bipolar transistors HBTs) for low power and high speed.
1B. Boudart, C. Gaquiere, and D. Theron, "Gate current analysis of LT-GaAs passivated MESFETs." Electronics Letters33, 1496-8 (1997).
2P. Schmid, K. M. Lipka, J. Ibbetson, N. Nguyen, U. Mishra, L. Pond, C. Weitzel, and E. Kohn, "High-temperature performance of GaAs-basaed HFET structure containing LT-AlGaAs and LT-GaAs." IEEE Electron Device Letters19, 225-7 (1998).
3R. V. V. V. Rao, T. C. Chong, W. S. Lau, L. S. Tan, C. Geng, and N. Lim, "Low frequency noise analysis of LT-GaAs and LT-Al0.3Ga0.7As MISFET active layers." Electronics Letters34, 2066-7 (1998).
4S.-G. Park, A. M. Weiner, M. R. Melloch, C. W. Sider, J. L. Sider, and A. J. Taylor, "High-power narrow-band terahertz generation using large-aperture photoconductors." IEEE Journal of Quantum Electronics35, 1257-68 (1999).
5M. Tani, K.-S. Lee, and X.-C. Zhang, "Detection of terahertz radiation with low-temperature-grown GaAs-based photoconductive antenna using 1.55 mm probe." Applied Physics Letters77, 1396-8 (2000).
6H. Reese, Y. J. Chiu, and E. Hu, "Low-temperature-grown GaAs enhanced wet thermal oxidation of Al0.98Ga0.02As." Applied Physics Letters73, 2624-6 (1998).
7P. Parikh, J. Ibbetson, U. Mishra, D. Docter, M. Le, K. Kiziloglu, D. Grider, J. Pusl, D. Widman, L. Kehias, and T. Jenkins, "Record Power-Added-Efficiency, Low-Voltage GOI (GaAs On Insulator) MESFET Technology for Wireless Applications." ieee Transactions on Microwave Theory and Techniques46, 2202-7 (1998).