Study On Gallium Nitride Strained Channel High Electron Mobility Transistor Device And Physical Model

With the reduction of device process size,strained silicon technology has become a major iterative means in improving the performance of silicon-based devices.With the rapid development of information and communication technology,semiconductor devices are required to move towards high-power and high-frequency band.Group III nitrides represented by gallium nitride（GaN）are applied to high-performance semiconductor devices.Strained GaN is similar to strained silicon and can significantly improve the channel electron mobility under tensile strain.However,the development of strained GaN is limited by the current process and strain measurement technology,The physical mechanism and mathematical model of strain effect in GaN high electron mobility transistor devices（HEMTs）need further study.The research of this paper will be divided into the following parts:1、In order to apply tensile strain to the GaN channel and further improve the current characteristics of AlGaN/GaN HEMTs,a strained GaN channel model is established and comprehensively demonstrated according to the strain theory and polarization theory,combined with the reported theoretical results of GaN strain effect.The theoretical calculation results show that under the influence of Indium composition x=0.02,0.04 and0.06 in the In_xGa_1-xN relaxation layer,the channel strain increases by 0.225%,0.450%and0.675%respectively,the AlGaN/GaN channel electron gas concentration increases slightly,and the GaN/In GaN channel electron gas concentration increases significantly.This paper considers that this result is caused by the polarization cancellation of AlGaN and GaN,and the difference of piezoelectric polarization factor,a GaN channel HEMT（SGC-HEMT）device structure is proposed.The channel strain of GaN is regulated by changing the Indium composition x of In_xGa_1-xN relaxation layer.The simulation results show that with the increase of channel strain,the threshold voltage of ideal SGC-HEMT device is linearly negative drift.When the Indium composition x of In_xGa_1-xN relaxation layer increases by0.02,the threshold voltage is negative drift of 0.67 V and the drain saturation current increases by 0.3 A/mm.At the same time,the rationality of the simulation results is mathematically analyzed based on the strain model.2、In order to improve the negative drift of SGC-HEMT threshold voltage and take into account the current characteristics of the device,a non-under-Gate strained channel GaN HEMT（SNGC-HEMT）device structure is proposed in this paper.The simulation results show that the threshold voltage basically does not change with x,which is-3.96 V,since no strain is applied to the channel under the gate of SNGC-HEMT.Under the influence of in composition x=0.02,0.04 and 0.06 in the In_xGa_1-xN relaxation layer,the drain saturation currents of SNGC-HEMT device are 0.914 A/mm,1.095 A/mm and 1.219A/mm respectively,which are increased by 30.63%,56.47%and 74.17%respectively compared with the 0.701 A/mm of traditional devices;In addition,through the simulation and analysis of the strain GaN channel thickness(T_SGC)of the device,the optimal T_SGC of SNGC-HEMT device is determined:T_SGC=4 nm.The effective mobility peaks of optimized SNGC-HEMT device are 259.61 cm²/V·s,281.34 cm²/V·s and 289.56 cm²/V·s respectively.Compared with 187.82 cm²/V·s of traditional AlGaN/GaN HEMT devices,the effective mobility peaks are increased by 38.23%,49.80%and 54.17%respectively.Compared with conventional AlGaN/GaN HEMT devices,SNGC-HEMT devices show obvious advantages in drain saturation current and effective mobility.However,with the increase of channel strain,the lifting effect of channel strain on the device gradually degenerates.In this paper,it is considered that the gradual degradation of the lifting effect of channel strain on the device mainly includes two reasons:one is that the non-under-Gate channel strain changes the electric field distribution of the under-Gate channel,and the other is that the defects introduced by channel strain aggravate the scattering of carriers.