Fabrication and Characterization of Metal-Ferroelectric-Gan Structures
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ABSTRACT GaN-based metal-ferroelectric-semiconductor (MFS) structure has been fabricated by using ferroelectric Pb(Zr0.53Ti0.47)O3 (PZT) instead of conventional oxides as gate insulators. The GaN and PZT films in the MFS structures have been characterized by various methods such as photoluminescence (PL), wide-angle X-ray diffraction (XRD) and high-resolution X-ray diffraction (HRXRD). The Electric properties of GaN MFS structure with different oxide thickness have been characterized by high-frequency C-V measurement. When the PZT films are as thick as 1 µm, the GaN active layers can approach inversion under the bias of 15V, which can not be observed in the traditional GaN MOS structures. When the PZT films are about 100 nm, the MFS structures can approach inversion just under 5V. All the marked improvements of C-V behaviors in GaN MFS structures are mainly attributed to the high dielectric constant and large polarization of the ferroelectric gate oxide.
I. INTRODUCTION Recently, the semiconductor gallium nitride (GaN) has been recognized for several decades for their potential and, recently, commercial viability in wide band optoelectronic device applications [1]. The electronic devices that can be used for high power and high temperature applications have also been fabricated, among which GaN-based MOSFETs are actively studied [2]. The traditional GaN MOS structures fabricated with conventional oxides, like SiO2 [3,4], Si3N4 [3], Ga2O3(Gd2O3) [4], as insulators have to be improved. One important reason is that large applied voltage, which is incompatible with most other electronic devices, is imposed on all the previous GaN MOS structures. In our work, ferroelectric oxides have been used in GaN MOS structures to address this problem because of large polarization provided by ferroelectric and the high dielectric constant of ferroelectric gate. Since the field-effect transistors (MFSFETs) was first proposed by Wu [5, 6], it has been extensively studied because of their applications in non-volatility and high speed memories and integration circuits [7-10]. Nowadays, the semiconductor used in metalferroelectric-semiconductor (MFS) structures usually is Si. The instability of the ferroelectric/Si interface due to interdiffusion between ferroelectrics and Si substrates has still impeded the development of the novel device [8]. Consequently, many kinds of buffer layers have been deposited between ferroelectrics and Si substrates to prevent the behavior of interdiffusion [11-13], which also decreases the control of ferroelectric polarization on the potential of Si surface. GaN is so stable that it can work without weight loss at 1000 0C[14]. GaN MFS structure is a good candidate to develop ferroelectric/semiconductor interface and MFSFETs with high-temperature stability.
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II. EXPERIMENTS In the GaN MFS structure developed in this work, n-type GaN active layer is grown by light radiant heating low-pressure metalorganic chemical vapor deposition (LRH-LPMOCVD) on the (0001) oriented sapphire (Al2O3) substrate wh
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