Electronics and sensors based on pyroelectric AlGaN/GaN heterostructures – Part B: Sensor applications

Abstract

In the present article recent results concerning sensor applications of AlGaN layers and AlGaN/GaN heterostructures are summarized. The piezoresistive effect in piezoelectric AlGaN layers is investigated and the dependence of the piezoresistive gauge factor on the Al content is attributed to the influence of strain induced piezoelectric fields. An enhancement of this effect is observed in AlGaN/GaN heterostructures, resulting in high longitudinal gauge factors.The response of gas sensitive Pt:GaN Schottky diodes to hydrogen and hydrogen containing gases is analyzed up to temperatures of 600°C and employed to realize gas sensitive field effect transistors which are demonstrated to operate up to 400°C. In addition, ion sensitive field effect transistors (ISFETs) have also been fabricated on the basis of AlGaN/GaN heterostructures. The GaN surface shows a high pH sensitivity which is attributed to the presence of a thin native metal oxide layer on the surface.

Humanitarian Demining Using an Insect Based Chemical Unmanned Aerial Vehicle

“…In addition, the limit of the sensitivity of the thin metal oxide chemo-sensing technology, and in particular the applicability to the particular case of the detection of leaking explosives has to be further assessed. It has been shown that the sensitivity of this type of technology can go up to few parts per million (ppm), providing a wide range sensitivity that allows for identification of organic compounds (Neubecker et al 1997;Eickhoff et al 2003). Nevertheless, the chemical traces of some explosives such as TNT are shown to be made of few parts per billion (ppb) (Rose et al 2005).…”

Fabrication and Characterization of GaN-Based Two Terminal Devices for Liquid Sensing

“…Both structures are grown on 430 μm sapphire substrates. The heteroepitaxial growth of the group III-nitrides on sapphire substrate allows the application of simple planar device structures [7]. The following AlN buffer layer is necessary as it dramatically improves the surface morphology and crystalline quality of the following undoped-GaN layer [13].…”

“…The following AlN buffer layer is necessary as it dramatically improves the surface morphology and crystalline quality of the following undoped-GaN layer [13]. Furthermore, the thermal expansion of the sapphire substrate is close to that of AlN and AlN is also often used as packaging materials for high temperature sensor [7]. For the bulk structure, Si doped-GaN channel is formed near to the surface of the top layer.…”

“…Group III-nitrides with wurtzite crystal structure are chemically stable semiconductors with high internal spontaneous and piezoelectric polarization, which make them highly suitable materials to create very sensitive but robust sensors for the detection of ions, gases and polar liquids [4,5]. Solids with a large band gap such as diamond or gallium nitride (GaN) are among the prime candidates for a variety of sensor applications, particularly at high temperatures and in harsh environments.…”

“…AlGaN/GaN heterostructures have been extremely useful for gas and liquid sensor due to primarily three reasons: 1) a high electron sheet carrier concentration channel induced by piezoelectric polarization of the strained AlGaN layer, 2) the carrier concentration which is strongly depends on the ambient [6,7] 3) an opportunity of on-chip co-integration with signal processing and communication circuit. In addition, sensors fabricated from these wide band-gap semiconductors could be readily integrated with solar blind UV detectors or high temperature, high power electronics with wireless communication circuits on the same chip to provide high speed transmission of the data.…”