Hydrogen Peroxide Measurements by MISFET and LET Structures with Rear Porous Silicon Layer and Metallic Nanoparticles

Abstract

In the paper hydrogen peroxide MISFET and LET sensor performance is investigated. As hydrogen peroxide is a product of many chemical reactions, especially biological reactions, peroxide sensors are now widely used for detection of another. In this work, a combination of two nanostructures that are now used for hydrogen peroxide detection – porous silicon and metal nanoparticles was used.A MISFET (metal-insulator-semiconductor field effect transistor) was chosen as the basic sensor but unlike conventional FET sensors sensitive area was formed on the rear side of the sensor. In the aim to simplify sensor structure a LET (light-effect transistor) with sensitive area on the rear side was also tested. LET structure was produced by the same technology as FET, but then subgate system was removed by chemical etching. Porous silicon was formed by metal-assisted chemical etching (MACE) that consists of two stages. During the first stage, metallic nanoparticles are deposited on the surface by chemical or physical deposition. During second one these particles become catalysts of chemical reaction and pores are formed under them. Pore shape and density depend on both stages conditions.Formation of porous silicon on the rear side leads to changes of substrate charge and influence gate-source curve as well as drain-source curve. Drain current for FET with an active area is lower due to the negative charge accumulated in porous silicon thanks to high tie connections concentration. Dependence of LET drain current on LED intensity (current) is almost linear and drain-source curves are similar to FET structure ones. FET samples with porous silicon/Pt and LET samples with porous silicon/Ag both show more stable and well-defined dependence of drain current on hydrogen peroxide concentration then samples without porous layer. All sensors have saturation of drain current from concentrations of hydrogen peroxide about 0.5-1% and dependence on concentration is first order exponential decay, obviously due to saturation of working area by reaction products or heating effect of hydrogen peroxide decomposition. In concentration range up to 0.3% hydrogen peroxide best sensitivity was demonstrated by LET sensor (574 μA/%), for FET sensor sensitivity is about 6 μA/% for MISFET without active area and about 8.3 μA/% for MISFET with active area. As Ag and Pt catalyst hydrogen peroxide decomposition, sensors with metal nanoparticles shows quicker reaction (maximum response less than in 3 minutes). To ensure accuracy and precision of measurements temperature and illumination of active area dependences of drain current should be taken into account. MISFET with porous silicon demonstrates typical for silicon structures exponential decay dependence of drain current on luminous flux and quasi-linear dependence on temperature Slopes are 34 μA/lm and 6.46 μA/˚C respectively.Hydrogen peroxide sensor with porous silicon shows good performance in both configuration – as MISFET and as LET structure. MISFET structure is more adjustable but have lower sensitivity (about 8 μA/% ) while LET structure is more simple and sensitive (up to 500 μA/% ). Use of both Ag and Pt nanoparticles decrease response time of sensor to 2-3 minutes.Ref 21, fig 17