Abstract
Integrating functional complex oxides with conventional (“non-oxide”) semiconductors emerges to be an important research field and has been attracting great interest. Because of their superior intrinsic material properties, such as a relatively high dielectric constant and polarization, the utilization of PbZr1-xTixO3 (PZT) materials as a dielectric layer is expected to greatly improve the performance of the GaN high electron mobility transistor. The functional PbZr1-xTixO3 exhibits quite different crystal structures and consequently physical properties depending on the composition. In this work we report the growth of full range of compositions of PZT films on MgO buffered GaN substrates. Besides revealing the temperature effect on phase formation and surface morphology, we demonstrated the strong effect of composition on the growth: pure (1 1 1) phase is formed in Ti-rich PZT (x > 0.48) while pyrochlore impurity phase is found in Zr-rich PZT (x < 0.48). By introducing an ultrathin Ti-rich PZT seed layer, we are able to achieve epitaxial growth of Zr-rich PZT. The epitaxial PZT films of different composition all exhibit good ferroelectric properties, showing great promise for future GaN device applications.
Highlights
The semiconductor GaN is an important material with many potential applications such as field effect transistor (FET) in high power and high frequency devices due to its direct, wide band gap of 3.45 eV at room temperature and high chemical and mechanical stability [1,2]
With an atomically flat ultrathin MgO buffer layer, we previously realized the epitaxial growth of highly crystalline PZT (x = 0.48) films with excellent ferroelectric properties, which opens the possibility to practically use advanced oxide materials in GaN high electron mobility transistor (HEMT) [13]
Different compositions are suitable for different types of applications, it is highly desired to study the epitaxial growth of different compositions of PZT on GaN
Summary
The semiconductor GaN is an important material with many potential applications such as field effect transistor (FET) in high power and high frequency devices due to its direct, wide band gap of 3.45 eV at room temperature and high chemical and mechanical stability [1,2]. The utilization of ferroelectric PbZr1-xTixO3 (PZT) materials as a dielectric layer is expected to further improve the performance of GaN/AlGaN high electron mobility transistor (HEMT). The highly incompatible crystal lattice, different lattice constant, and chemical reactivity between PZT and GaN hinder the epitaxial growth of PZT [8,9,10,11,12,13]. With an atomically flat ultrathin MgO buffer layer, we previously realized the epitaxial growth of highly crystalline PZT (x = 0.48) films with excellent ferroelectric properties, which opens the possibility to practically use advanced oxide materials in GaN HEMTs [13]. The physical properties of these (1 1 1) PZT layers on GaN are found to strongly depend on the composition, paving a path to diverse device applications
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