Ferroelectric Gates for Modulation of 2D Electron Gas at GaN/AlGaN Interfaces
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0902-T05-05.1
Ferroelectric Gates for Modulation of 2D Electron Gas at GaN/AlGaN Interfaces Igor Stolichnov, Lisa Malin, Paul Muralt and Nava Setter Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratory of Ceramics CH-1015 Lausanne, Switzerland ABSTRACT
The Pb(Zr,Ti)O3 ferroelectric gate was successfully integrated into the GaN/AlGaN heterostructure with 2D electron gas. The processing conditions were optimized in a way to obtain high quality textured Pb(Zr,Ti)O3 films without destroying the 2D gas situated as close to the interface as 20nm. Study of transport properties in this system demonstrates a possibility to control the 2D gas by switching the spontaneous polarization in the gate. Concentration and mobility of electrons in the 2D gas were monitored using Hall effect and resistivity measurements in a wide temperature range from 4.2K to 300K. The polarization oriented in the direction “from bottom to top” provokes a partial depletion effect in the channel resulting in a conductivity decrease. A correlation between the depletion effect in 2D gas and the change of the spontaneous polarization with temperature has been observed. The depletion effect is found to be reversible so that the initial conductivity in 2D gas can be restored by inversing the spontaneous polarization in the gate. These results suggest that ferroelectric gates integrated into systems with 2D electron gas may be potentially interesting for a number of experiments and applications as a flexible and nondestructive way of making rewritable nanopatterns on semiconductor heterostructures.
INTRODUCTION Ferroelectrics attract much interest as potential gate materials for semiconductor fieldeffect devices 1 due to a number of potential applications, in particular nonvolatile memories with non-destructive reading2. However, difficulties with integration of the ferroelectric materials into the silicon-based systems severely limit the progress in this field. In this context, selection of the appropriate semiconductor material compatible with the high-temperature processes used for ferroelectrics is an important issue for development of devices of this kind. AlGaN/GaN heterostructures that have been intensively studied over last decade in view of hightemperature and high-power electronic applications look to be promising candidates for integrated ferroelectric/semiconductor devices because of the high thermal and chemical stability. Recent reports on the successful deposition of Pb(Zr,Ti)O3 (PZT) 3-6 and BaTiO37 ferroelectric layers on GaN demonstrate the good potential of this approach. A multilayer structure comprising a layer of PZT deposited on top of the GaN/AlGaN heterostructure with 2D electron gas (2D gas) showed a hysteretic capacitance-voltage characteristic6. This effect was interpreted in terms of influence of the spontaneous polarization in the ferroelectric layer on the carrier concentration in 2D gas suggesting the possibility to use the system for nonvolatile memories. However, no direct evidence of the control of the transport p
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