An Ultrathin Single Crystalline Relaxor Ferroelectric Integrated on a High Mobility Semiconductor

Abstract

The epitaxial growth of multifunctional oxides on semiconductors has opened a pathway to introduce new functionalities to semiconductor device technologies. In particular, the integration of gate materials that enable nonvolatile or hysteretic functionality in field-effect transistors could lead to device technologies that consume less power or allow for novel modalities in computing. Here we present electrical characterization of ultrathin single crystalline SrZrTiO (x = 0.7) films epitaxially grown on a high mobility semiconductor, Ge. Epitaxial films of SrZrTiO exhibit relaxor behavior, characterized by a hysteretic polarization that can modulate the surface potential of Ge. We find that gate layers as thin as 5 nm corresponding to an equivalent-oxide thickness of just 1.0 nm exhibit a ∼2 V hysteretic window in the capacitance-voltage characteristics. The development of hysteretic metal-oxide-semiconductor capacitors with nanoscale gate thicknesses opens new vistas for nanoelectronic devices.

Epitaxial Oxides on Semiconductors: From Fundamentals to New Devices

“…One approach to mitigate the type‐II band alignment is to insert a buffer layer that has a type‐I arrangement between the ferroelectric and semiconductor, as was demonstrated by Murphy et al for BTO grown on MgO buffered GaAs . Another approach is to use relaxor materials that have a type‐I band offset with respect to the semiconductor, as demonstrated by Moghadam et al in their study of SrZr 0.7 Ti 0.3 O 3 (SZTO) on Ge . A switchable persistent polarization could be induced through applied fields, as indicated in both amplitude and phase response of PFM and piezo‐response spectroscopy measurements.…”

“…Kolpak et al found that this fixed polarization was germane to a variety of interfacial compositions that mediate epitaxy between STO and Si . Such a fixed polarization inhibits switching of a ferroelectric layer, unless disrupted through the formation of a native Si or Ge oxide layer . However, bonding at the (100) surface also presents an opportunity.…”

Layer-resolved band bending at the n−SrTiO3(001)/p−Ge(001) interface

“…Due to the sizeable lattice mismatch between STO and Ge, STO epitaxial films on Ge may exhibit ferroelectric distortions, as have also been reported for STO/Si(001) [9,10]. Indeed, relaxor ferroelectric behavior has been observed for SrZr0.7Ti0.3O3/Ge(001) [16]. In addition to having substantially higher room-temperature mobilities for both electrons and holes than Si, as well as a smaller bandgap (0.66 eV) to facilitate photovoltaic and photoelectrochemical energy conversion, Ge is more oxidation resistant than Si.…”

Low Subthreshold Slope AlGaN/GaN MOS-HEMT with Spike-Annealed HfO2 Gate Dielectric

“…As the ferroelectric property is dependent on the domains, crystallinity plays a critical role in the magnitude of spontaneous polarization. Therefore, this work followed the method suggested in [24] to perform PUND on our MOSCAP [22][23][24]. Figure 3a shows the current (orange) measured in response to the PUND pulses; P and N voltage pulses correspond to switching polarization.…”

“…To reduce the gate leakage and drain current collapse, for example, MOS-HEMTs have been developed with various high-k dielectrics such as Al 2 O 3 , Y 2 O 3 , and HfO 2 [6][7][8]. HfO 2 is a very promising gate dielectric for HEMTs due to its large bandgap (5.3-5.8 eV) and high dielectric constant (20)(21)(22)(23)(24)(25).…”