Development of nitrides based on InN for sensor applications

Abstract

The unique properties of the III nitrides, their high radiation hardness, high thermal stability and wide direct band gap makes them interesting for its application in electronic and opto-electronic devices. AlInN is of particular interest because its band gap energy can be tuned between 0.7 to 6.2 eV depending on the alloy composition so that it is possible to engineer the electronic structure for each specific application.It has been grown by different techniques, among them, radio frequency reactive sputtering allows deposition in a wide range of substrate types and temperatures, these advantages together with the low cost of the technique are the reasons for which sputtering technique has been selected for this Thesis.Several substrates such as sapphire, p silicon (111), glass and optical fibers have been used for growing AlInN by radio frequency reactive sputtering. The growth conditions of AlInN have been optimized for the different substrates by studying its structural, chemical, morphological, electrical and optical properties. AlInN layers grown with the best growth conditions were processed into devices. The layers grown on sapphire substrates were processed into photoconductors. Their characterization shows a strongly sublinear response with the optical power and a smooth drop of the responsivity for excitation below the band gap. Also these devices present persistent photoconductivity effects. On the other hand, the layers grown on p silicon (111) have been processed as solar cells, it has been demonstrated that the devices change their behavior when they are irradiated with light, the IV characteristics and external quantum efficiency are presented and show that the use of a 4 nm AlN buffer layer improves the device properties. The layers grown at low substrate temperature on optical fibers have been studied as surface plasmon resonance sensors. It has been demonstrated that the homogeneity of the ternary compound acting as dielectric layer is very important to obtain better sensitivities and narrower transmittance dips. The use of different compositions in the dielectric layer allows the selection of the transmittance resonance dip. The metal layer thickness effect has also been studied showing that higher metal thicknesses increase the sensitivity with an increase in the full width at half maximum of the transmittance dip, so it has to be chosen taking into account the use of the sensor.