GaN-based diodes and transistors for chemical, gas, biological and pressure sensing

Abstract

There is renewed emphasis on development of robust solid-state sensors ca- pable of uncooled operation in harsh environments. The sensors should be capable of detecting chemical, gas, biological or radiation releases as well as sending signals to central monitoring locations. We discuss the advances in use of GaN-based solid-state sensors for these applications. AlGaN/GaN high elec- tron mobility transistors (HEMTs) show a strong dependence of source/drain current on the piezoelectric polarization-induced two-dimensional electron gas (2DEG). Furthermore, spontaneous and piezoelectric polarization-induced sur- face and interface charges can be used to develop very sensitive but robust sen- sors to detect gases, polar liquids and mechanical pressure. AlGaN/GaN HEMT structures have been demonstrated to exhibit large changes in source-drain current upon exposing the gate region to various block co-polymer solutions. Pt-gated GaN Schottky diode sa nd Sc 2O3/AlGaN/GaN metal-oxide semicon- ductor diodes also show large change in forward currents upon exposure to H2. Of particular interest is detection of ethylene (C2H4), which has strong double bonds and hence is difficult to dissociate at modest temperatures. Apart from combustion gas sensing, the AlGaN/GaN heterostructure devices can be used as sensitive detectors of pressure changes. In addition, large changes in source- drain current of the AlGaN/GaN HEMT sensors can be detected upon adsorption of biological species on the semiconductor surface. Finally, the nitrides pro- vide an ideal platform for fabrication o fs urface acoustic wave (SAW) devices. The GaN-based devices thus appear promising for a wide range of chemical, biological, combustion gas, polar liquid, strain and high temperature pressure- sensing applications. In addition, the sensors are compatible with high bit-rate wireless communication systems that facilitate their use in remote arrays. (Some figures in this article are in colour only in the electronic version)