2 results
Epitaxial Growth of High-κ Dielectrics for GaN MOSFETs
- Jesse S. Jur, Ginger D. Wheeler, Matthew T. Veety, Daniel J. Lichtenwalner, Douglas W. Barlage, Mark A. L. Johnson
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1068 / 2008
- Published online by Cambridge University Press:
- 01 February 2011, 1068-C08-02
- Print publication:
- 2008
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- Article
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High-dielectric constant (high-κ) oxide growth on hexagonal-GaN (on sapphire) is examined for potential use in enhancement-mode metal oxide semiconductor field effect transistor (MOSFET). Enhancement-mode MOSFET devices (ns > 4×1013 cm−2) offer significant performance advantages, such as greater efficiency and scalability, as compared to heterojunction field effect transistor (HFET) devices for use in high power and high frequency GaN-based devices. High leakage current and current collapse at high drive conditions suggests that the use of a high-κ insulating layer is principle for enhancement-mode MOSFET development. In this work, rare earth oxides (Sc, La, etc.) are explored due to their ideal combination of permittivity and high band gap energy. However, a substantial lattice mismatch (9-21%) between the rare earth oxides and the GaN substrate results in mid-gap defect state densities and growth dislocations. The epitaxial growth of the rare earth oxides by molecular beam epitaxy (MBE) on native oxide passivated-GaN is examined in an effort to minimize these growth related defects and other growth-related limitations. Growth of the oxide on GaN is characterized analytically by RHEED, XRD, and XPS. Preliminary MOS electrical analysis of a 50 Å La2O3 on GaN shows superior leakage performance as compared to significantly thicker Si3N4 dielectric.
Prospect for III-Nitride Heterojunction MOSFET Structures and Devices
- M. A. L. Johnson, D. W. Barlage, Dave Braddock
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- Journal:
- MRS Online Proceedings Library Archive / Volume 829 / 2004
- Published online by Cambridge University Press:
- 26 February 2011, B7.7
- Print publication:
- 2004
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Heterojunction field effect transistors (HFET) for high-frequency and high-power electronics have been an area of active research in recent years as a key enabling technology for applications ranging from wireless communications to power distribution. III-Nitride semiconductors are a leading candidate for fulfilling the material requirements of these devices based on the combination of large bandgap energy, high thermal conductivity, high electron mobility and saturated electron velocity. While III-Nitride HFETs have demonstrated remarkable advances, serious materials related limitations still exist, primarily related to charge states and trapping effects at the semiconductor surface. Several groups have investigated solutions such as the deposition of dielectric passivation layers and asymmetric field-plate gate geometries for controlling the influence of trap states near the metal/semiconductor FET interface. We have demonstrated a metal-oxide semiconductor FET (MOSFET) with a substantially unpinned interface which is capable of establishing substantial charge accumulation under the gate. These III-Nitride MOSFETs may be designed to operate in either depletion mode or enhancement mode. GaN/InGaN heterojunction MOSFETs exhibit enhancement mode peak transconductance at gate voltages Vg>+5V, corresponding to energy greater than the bandgap of the underlying semiconductor which provides strong evidence of an unpinned MOS interface. Additionally III-Nitride MOSFETs eliminate the need for field plate gate structures as the electric field geometry in the gate-drain region changes limiting the tunneling of charge to unfilled surface states. In depletion mode, low-rf dispersion InGaN/GaN MOSFETs exhibit excellent microwave with ft = 8GHz for optically defined gates dimensions.
We review the history of compound semiconductor MOSFET development and overlaying these developments with recent advances in the III-Nitride materials and device research. Differences in chemistry of III-Nitrides relative to all other compound semiconductors and the epitaxial deposition of gate-oxides such as Gadolinium Gallium Oxide (GGO), opens the possibility for dramatically improved devices at microwave and mm-wave frequencies as well as power MOSFET rectifiers. Initial III-Nitride MOSFETs results are presented as well as a quaternary thermodynamic framework for the stability of gate-oxide on nitride semiconductors. We also identify key materials related research challenges expected to impact the ongoing development of III-Nitride MOSFETs.