Research On The Sensing Performance Of GaN-based High Electron Mobility Transistors

?-nitride semiconductor materials have broad application prospects in the fields of photoelectric detection,lighting display,high power and high frequency electron device,etc.due to their advantages of wide band gap,high thermal conductivity,strong breakdown voltage,high temperature resistance,high radiation resistance,etc.A slight change in the external environment can cause a change of two-dimensional electron gas(2DEG)density in GaN-based high electron mobility transistor(HEMT),which causes a significant change in the output current of the device,so GaN-based HEMTs have attracted extensive attention and research in the field of sensing technology.In recent years,the surface modification of various detection substances has been focused on when the research is about GaN-based HEMT sensing.The detection of a variety of gases,heavy metal ions,harmful anions and biological macromolecules has been achieved.However,preempting the use of HEMTs for more sensing detection areas,further improvement of their detection sensitivity is needed,i.e.,to improve the ability of surface charge to modulate device performance.In this paper,the regulation law of additional surface charge on the performance of Ga-polar and N-polar GaN based HEMT and the effect of structural parameters on the sensing performance of the device are studied systematically by self-consistently solving the Schrodinger equation,Poisson equation and carrier continuity equation.The main research contents and research results are as follows:1?The sensing mechanism which is the effect of surface charges with different concentrations on the performance of AlGaN/GaN HEMT is investigated.The results show that2 DEG density and saturation output current of both AlGaN/GaN gateless and gated HEMT increase with increasing positive surface charge density and decrease with increasing negative surface charge density.Compared with gated HEMT,surface charge has a stronger ability to modulate the performance of gateless HEMT,i.e.,the surface sensing sensitivity of gateless HEMT is higher.The modulation of surface charges on the performance of the device is mainly attributed to the variation of the energy band structure in heterojunction and built-in electric field.2?The effect of AlGaN barrier layer thickness on the ability of surface charge to modulate the device is investigated.The results show that although increasing AlGaN barrier layer thickness within a certain range can increase the saturation output current and improve the power characteristics of the device,the ability of surface charges to regulate the performance of both gated and gateless HEMT decreases with the increase of barrier layer thickness,i.e.,the detection sensitivity of the sensor decreases as barrier layer thickness increases.Therefore,in the optimization design of the material stucture of HEMT sensor,barrier layer thickness should be appropriately reduced in the range larger than the critical thickness.3?The sensing mechanism of N-polar AlGaN/GaN gateless HEMT and the effect of GaN channel layer thickness and AlGaN back barrier layer thickness on sensing performance of the device are investigated.It is found that,compared with traditional Ga-polar gateless HEMT,the performance of N-polar gateless HEMT is more sensitive to surface charge.Therefore,N-polar gateless HEMT has higher sensing sensitivity.In addition,with the same additional surface charges,the saturation output current and 2DEG density of Npolar gateless HEMT both increase with the increase of GaN channel layer thickness as well as AlGaN back barrier layer thickness(within a certain thickness range).However,with the same additional surface change,the larger the GaN channel layer thickness,the smaller the relative change of saturation output current and 2DEG density,resulting in lower sensing sensitivity of the device.Therefore,based on the above research results,it is known that in order to obtain GaN-based HEMT sensors with high detection sensitivity,the N-polar gateless AlGaN/GaN HEMT structure should be selected under the premise of ensuring the quality of material growth,and GaN channel layer thickness should be appropriately thinned while ensuring a higher 2DEG density in the channel.