Study Of Surface Hydroxylation Of AlGaN/GaN HEMT Biosensors

Group III nitrides exhibit strong spontaneous polarization and piezoelectric polarization effects,and polarization induces the formation of two-dimensional electron gas at their heterojunction interfaces.The concentration of two-dimensional electron gas is strongly influenced by the potential of the surface.Because of its high gate charge sensitivity,AlGaN/GaN-based high electron mobility transistors(HEMTs)are promising as biosensors.Surface modification of AlGaN/GaN can improve the biocompatibility of the sensor gate region and improve the performance of the biosensor.The acquisition of a hydrophilic surface is critical to the improvement of the biocompatibility of the sensor grid.Hydroxyl groups can improve the hydrophilicity of the sensor surface.This paper mainly aims at the modification and characterization of the surface hydroxyl groups in the gate region of AlGaN/GaN HEMTs,as well as the adsorption characteristics of the hydroxyl groups on the surface of the sensor and the coverage of surface hydroxyl groups by first-principles calculation.In this paper,the GaN(0001)surface of wurtzite structure is selected as the research object.The main research contents are as follows:Firstly,the hydroxylation of GaN(0001)surface was carried out under different conditions.By analyzing the static contact angle of water droplets and the surface topography of atomic force microscopy,we try to find the processing temperature and time that make the surface hydroxylation effect the best.With time,it provides mature process conditions for surface hydroxylation treatment during biosensor fabrication.Subsequently,we studied the hydroxylation effect of piranha solution on the GaN(0001)surface by contrast experiments.X-ray photoelectron spectroscopy(XPS)was used to characterize the movement of surface atomic peaks after different surface treatment methods,the way in which the hydroxyl group is attached to the GaN(0001)surface is described.The GaN(0001)surface has a strong hydroxylation ability due to the presence of dangling bonds,and the piranha solution is easily hydroxylated to form a hydrophilic surface.Finally,we use the CASTEP module in Materials Studio software to optimize the wurtzite GaN unit cell using a first-principles method based on density functional theory.In-depth analysis of density of states,Mulliken charge,differential charge density,and energy band structure.The adsorption energy of hydroxyl at different adsorption sites on the GaN(0001)surface and the adsorption energy and adsorption configuration of different hydroxyl groups were calculated.The phase diagram between Gibbs free energy and hydroxyl chemical potential was obtained.The electronic structure and density of states of the most stable hydroxyl group adsorbed on the surface of GaN(0001)were analyzed in detail.The adsorption behavior of hydroxyl groups on the GaN(0001)surface at the atomic level is described by theoretical calculations,which is instructive for the hydrophilic surface in the biosensor fabrication process.The extent of surface hydroxylation during the fabrication of high electron mobility transistor biosensors for current AlGaN/GaN is highly dependent on the process.In this paper,the process conditions of hydroxylation of biosensors were explored in detail,and the adsorption behavior of hydroxyl groups was revealed at the atomic level by theoretical calculations,which provided a theoretical explanation for the surface hydroxylation process of biosensors.