Validation of a triangular quantum well model for GaN-based HEMTs used in pH and dipole moment sensing

Abstract

Gallium nitride (GaN) is a relatively new semiconductor material that has the potential of replacing gallium arsenide (GaAs) in some of the more recent technological applications, for example chemical sensor applications. In this paper, we introduce a triangular quantum well model for an undoped AlGaN/GaN high electron mobility transistor (HEMT) structure used as a chemical and biological sensor for pH and dipole moment measurements of polar liquids. We have performed theoretical calculations related to the HEMT characteristics and we have compared them with experimental measurements carried out in many previous papers. These calculations include the current–voltage (I–V) characteristics of the device, the surface potential, the change in the drain current with the dipole moment and the drain current as a function of pH. The results exhibit good agreement with experimental measurements for different polar liquids and electrolyte solutions. It is also found that the drain current of the device exhibits a large linear variation with the dipole moment, and that the surface potential and the drain current depend strongly on the pH. Therefore, it can distinguish molecules with slightly different dipole moments and solutions with small variations in pH. The ability of the device to sense biomolecules (such as proteins) with very large dipole moments is investigated.

Synchrotron-based XPS studies of AlGaN and GaN surface chemistry and its relationship to ion sensor behaviour

“…The spontaneous piezoelectric polarisation occurring within AlGaN/GaN heterostructures of wurzite crystal structure has interested many researchers [13]. These polarisation effects result in a two dimensional electron gas (2DEG) layer consisting of high mobility electrons confined by a quasi-triangular quantum well at the AlGaN/GaN interface.…”

Charging mechanism of AlGaN/GaN open-gate pH sensor and electrolyte interface

“…The oxide surface-electrolyte interface is approximated by an electrical double layer (DL) model. The surface complexation processes can be described as [3,10] > ‫ܪܱܵ‬ + ‫ܪ‬…”

“…where ߰ represents the surface potential and ߰ ௗ represents the Stern potential. For a 1:1 (M + L -) electrolyte, electrical charge at the hypothetical parallel planes can be obtained using the modified Grahame equation [10]…”

“…An analytical model [14] is used to simulate the sensitivity of the device to the changes of pH. The device characteristics are the same as those of the device studied in reference [10,15]. The AlGaN/GaN heterostructure is grown on sapphire by metal-organic vapor phase epitaxy with aluminum composition of 0.23 and AlGaN thickness of 22nm.…”

Method to Predict and Optimize Charge Sensitivity of Ungated AlGaN/GaN HEMT-Based Ion Sensor Without Use of Reference Electrode

“…Ion sensitivity in reference electrode free sensors has been shown to depend on AlGaN/GaN composition [14], which is not surprising given that the heterostructure design determines sheet carrier density. While carrier charge density and mobility have been theoretical calculated for various AlGaN/GaN FET structures in the context of transistor operation, and to a limited extent to explain the behaviour of ungated AlGaN/GaN FET sensors [15], such calculations have yet to be systematically deployed to investigate the sensitivity limits of reference electrode free sensors, and/or to determine design parameters for practical sensor optimization.…”