Solution processed Li5AlO4 dielectric for low voltage transistor fabrication and its application in metal oxide/quantum dot heterojunction phototransistors. Issue 4 (8th January 2018)

• Record Type: Journal Article
• Authors: Sharma, Anand; Chourasia, Nitesh K.; Sugathan, Anumol; Kumar, Yogesh; Jit, Satyabrata; Liu, Shun-Wei; Pandey, Anshu; Biring, Sajal; Pal, Bhola N.
• Is Part Of: Journal of materials chemistry. Volume 6:Issue 4(2017)
• Page Start: 790
• Page End: 798
• Publication Date: 2018-01-08
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c7tc05074g
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Li5 AlO4 dielectric for low voltage transistor: Its application in metal oxide/quantum dot heterojunction phototransistors. Abstract : Li5 AlO4, a well-known material for solid state electrolyte application, has never been considered hitherto as a gate dielectric of metal oxide thin film transistors (TFTs). Here we demonstrate the salient features of Li5 AlO4 as a gate dielectric outperforming the conventional inorganic dielectrics used in TFTs. The high dielectric constant ( k ) of this insulator has been achieved by utilizing the improved capacitance contributed by mobile lithium ions (Li + ) within the dielectric film. We have synthesized this dielectric via a cost-effective sol–gel method followed by a low-temperature annealing process yielding three phases such as amorphous-Li5 AlO4 (a-Li5 AlO4 ), α-Li5 AlO4, and β-Li5 AlO4 under different annealing conditions. Optimized TFTs fabricated with all of these three phases of Li5 AlO4 on top of a highly doped silicon (p ++ -Si) wafer and a solution processed semiconducting layer of indium zinc oxide (IZO) exhibit an excellent TFT performance at different operating voltages. Among these three different types of TFTs, the device with an α-Li5 AlO4 gate dielectric annealed at 500 °C shows the best device performance with an on/off ratio of 5 × 10 4 and an electron mobility of 21.4 ± 2.16 cm 2 V −1 s −1 . In addition, this device requires the least drain voltage (<2 V) to reach the saturation drain current due to the higher Li + mobility of the α-Li5 AlO4 gate dielectric. This TFT performance on the p ++ -Si substrate is superior to that of a previously reported device with a sodium beta-alumina (SBA) gate dielectric, where the percentage of mobile ions within the dielectric material was comparatively much lower. Moreover, this dielectric requires ∼300 °C lower annealing temperature compared to the SBA dielectric. A metal oxide/quantum dot heterojunction phototransistor was fabricated by coating an IZO TFT with colloidal lead sulphide (PbS) quantum dots that shows a responsivity and a response time of 4.5 × 10 −4 A W −1 and 2.2 s respectively.