A high-quality (that is, low surface state density) oxide does not exist for GaAs. This has been known 'forever', and is why Si MOSFETs are the dominant electronic device by far. (As a benchmark, the surface state density for Si- SiO2 is equal to or less than 1E10 cm^-2.) On the other hand, there have been some papers which show possible approaches. One is: Nitride-based passivation of GaAs for reduced surface state density Hariu, T. Suzuki, N. Matsushita, K. Shibata, Y. IEEE International Electron Devices Meeting, 1978 Page(s): 598 - 599 They use gallium oxynitride deposited on GaAs, with a nitrogen anneal. Al2O3 insulator is used in: Microelectronics Reliability Volume 47, Issue 12, December 2007, Pages 2082-2087 Electrical measurements of voltage stressed Al2O3/GaAs MOSFET Z. Tanga, P.D. Yeb, D. Leea and C.R. Wiea Frankly, the VT shifts and gate current look awful, but no mention is made of SS density. ALD Al2O3 is discussed in the next reference, which suggest good characteristics are at least possible: Processing and Characterization of III-V Compound Semiconductor MOSFETs Using Atomic Layer Deposited Gate Dielectrics Book Series Advanced Microelectronics ISSN 1437-0387 Volume Volume 27 Book Advanced Gate Stacks for High-Mobility Semiconductors Publisher Springer Berlin Heidelberg DOI 10.1007/978-3-540-71491-0 Copyright 2007 ISBN 978-3-540-71490-3 (Print) 978-3-540-71491-0 (Online) DOI 10.1007/978-3-540-71491-0_16 Pages 341-361 Subject Collection Engineering SpringerLink Date Tuesday, January 01, 2008 Finally, Ga2O3(Gd2O3) ALD oxide insulator is used in the last ref, again with purported good effect (but for me the gate leakage is very, very high): Jpn. J. Appl. Phys. 46 (2007) pp. 3167-3180 III-V Metal-Oxide-Semiconductor Field-Effect Transistors with High κ Dielectrics Minghwei Hong, J. Raynien Kwo1, Pei-chun Tsai, Yaochung Chang, Mao-Lin Huang, Chih-ping Chen, and Tsung-da Lin Al Henning ahenning@nanoink.net -----Original Message----- From: mikas remeika [mailto:remeika@physics.ucsd.edu] Sent: Tuesday, August 03, 2010 3:05 PM To: General MEMS discussion Subject: [mems-talk] Surface states between GaAs and SiO2 Hello, everyone, I am working with a device that involves a layer of SiO2 sputtered on top of epitaxially grown GaAs. It appears that there is a large number of surface states that form at the interface (GaAs-SiO2) that effectively screen any electric fields that are applied perpendicular to the surface. Could anyone point me to some literature on eliminating these surface states? Also, is there another insulating NIR-transparent material that would not form such surface states at the interface with GaAs? To give a bit mode detail, I'm trying to fabricate a capacitor-like device where the half the dielectric is SiO2 and half is GaAs. It is very important for the potential to drop linearly in the device so that the field inside a material would only depend on the dielectric constant of the material. What I am getting right now is that all field is screened by the interface between SiO2 and GaAs. thank you, -mikas