Aug 31, 2012
Ferroelectricity and light control current in new transistors
Ferroelectric materials such as Pb(Zr0.3Ti0.7)O3 (PZT) with up and down remnant polarizations have been employed in non-volatile ferroelectric field effect memories as gate dielectrics. PZT is also pyroelectric, which means that the polarization properties can be modified with temperature. Inspired by this characteristic, researchers have fabricated a single ZnO nanowire (NW) field effect transistor (FET) on a PZT substrate. The team found that the drain current in a single ZnO NW could be modulated by an optothermal gating mechanism using PZT as the gate dielectric. Furthermore, the scientists obtained a maximum current sensitivity of 25 nA/mW for down polarization at a drain field of 83 kV/m, which is about three orders of magnitude higher than the typical 20 nA/W at a drain field of 50 kV/m for photogating transistors based on a carbon nanotube on SiO2/Si substrate architecture.
An infrared (IR) laser with a wavelength of 1064 nm was used as an optothermal source. The drain current in the ZnO NW can be increased or decreased by the IR illumination depending on the polarization orientation of the PZT substrate. For example, as shown in the figure, when the n-type ZnO NW is placed on top of the PZT substrate with up polarization, the bound positive charges on the PZT surface attract the electron carriers in the ZnO NW. When the PZT was illuminated by the IR laser, the increase in temperature reduced the polarization of the material and thus decreased the density of the positive bound charges near the nanowire. As a result, the electron carrier concentration in the ZnO NW decreases resulting in a decreased drain current. On the other hand, IR illumination on a PZT with down polarization decreases the polarization and negative bound charge density near the nanowire. Consequently, the electron carrier concentration in the ZnO NW increases and thereby increases the drain current.
Suits remote or wireless applications
It is known that when the laser is in the UV range, photocurrent can be generated in ZnO. Consequently, combining the photocurrent behaviour in the UV range and the optothermal gating effect in the IR range, broadens the opportunities for nanoscale optoelectronic devices. The optothermal feature of the device is especially suitable for remote or wireless applications.
Additional information can be found in the journal Nanotechnology.
About the author
The research was a joint effort to bring together the semiconductor expertise of Prof. Yang-Fang Chen’s group at National Taiwan University (NTU) and the piezoelectric expertise of Prof. Wan Y Shih and Wei-Heng Shih at Drexel University. The research was performed at NTU in Taipei, Taiwan, with many visits of the Drexel team including Wei-Heng Shih’s sabbatical leave. The work was supported by the National Science Council of Taiwan (NSC 99-2119-m-002-019-MY3) and the Ministry of Education of the Republic of China (10R80908-03). Chun-Yi Hsieh is a PhD student in Department of Physics at NTU. He performed the experiments and was supported by fellow PhD students, Meng-Lin Lu, Ju-Ying Chen and Yung-Ting Chen. Prof. Yang-Fang Chen is the leader of semiconducting group at Department of Physics of NTU. His group studies fabrication and characterization of compound quantum dots, plasmonics, photonic crystals and semiconductors. Wan Y Shih is an associate professor in the School of Biomedical Engineering, Science and Health Systems at Drexel University. She has developed piezoelectric microcantilever sensors and piezoelectric fingers for biomedical applications. Wei-Heng Shih is a professor in the Department of Materials Science and Engineering at Drexel University. He studies the colloidal processing of nanocrystals and piezoelectric materials and their applications in biomedical and electronic devices.