Study On Thermal Stability And Performance Of AlGaN/GaN HEMT With Recessed-Gate And Oxygen Plasma Treatment

AlGaN/GaN HEMTs have made great progress in microwave power applications,and more application potential remains to be explored.The conductive channel exists at 0 gate bias due to the strong polarization effect of AlGaN/GaN heterojunction,which makes HEMT a perfect device for microwave power application.But for power electronics and digital logic applications,depletion devices have some deficiencies.First of all,an additional voltage bias is needed to turn the device off if the circuit system is in standby,which increases the power consumption and safety risks.Furthermore,enhancement-mode devices are needed to realize logic functions under the existing digital circuit design rules.To promote the application of HEMT devices in power electronics and digital circuits,it is significant to do some research on the enhancement mode AlGaN/GaN HEMT devices through analyzing its characteristics and reliability.In this paper,based on the experimental plan of recessed-gate and oxygen plasma treatment,characteristics and temperature stability of devices with different experimental conditions are studiedFirstly,AlGaN/GaN HEMTs with different recessed depths and oxygen plasma conditions were fabricated using the laboratory standard GaN device process.The device threshold voltage of 8nm recessed depth combined with RF power of 40W and treatment time of 60s oxygen plasma processing conditions was+0.4V,which achieved enhancement mode successfully.The device saturation current density at V_GS=3V is nearly 400 mA/mm,the maximum on/off ratio is 10⁷,and the peak transconductance is 163 mS/mm.It is found that the oxygen plasma treatment can positive shift the device threshold voltage more than 1.5V and decrease the gate leakage current at least two orders of magnitude.At the same time,the threshold voltage could be further positive shifted and the gate leakage current could be further reduced with increasing of the oxygen plasma treatment time or RF power.In addition,the oxidation effect of oxygen plasma treatment is more obviously with the increase of recessed depth.However,the degradation in peak transconductance and current density becomes innegligible.The interface states and defect densities of the recessed gate and oxygen plasma treatment devices were further analyzed using the double-pulse I-V and frequency-dependent capacitance and conductance measurements.The double-pulse test results show that the current collapse of conventional and trench gate devices is 4%,8.4%,10.5%,and 14.6%,respectively.The current collapse ratio of recessed-gate devices can be greatly dropped to between 5%and 6%after reasonable oxygen plasma treatment.This result means that the oxygen treatment can reduce the interface trap density that induced due to gate recess etching.The longer time and larger power of the oxygen plasma treatment increases the value of current collapse,where the ion damage introduced by the oxygen plasma begins to be dominant.The results of frequency-dependent capacitance and conductance measurements show that compared with conventional devices,the recessed gate device has a smaller trap time constant,a higher trap density,and the oxygen plasma treatment device has a deeper trap-level distribution and a lower trap density.The temperature stability of recessed gate and oxygen plasma treatment devices is further studied in this paper.An on-line temperature test in the range of 25-300? was carried on firstly.The characteristics of the DC and Schottky characteristics of the device as a function of temperature,and before/after annealing were analyzed and discussed.The comparison of the temperature variation test results between the conventional device and the recessed-gate with oxygen plasma treatment device shows that the threshold voltage of the two devices maintains a good stability at a lower temperature range,where the?35?V_th is less than 0.1V.However,the threshold voltage of recessed-gate with oxygen plasma treatment device shows a large negative shift of about 0.2V in the temperature range of150?-300?.In terms of subthreshold characteristics,two devices show an increase subthreshold slope value with increasing temperature,but the recessed-gate with oxygen plasma treatment device is larger.In addition,the saturation current density,transconductance peak,and leakage with temperature of the two devices show a similar continuous decline trend.Secondly,the rapid annealing experiments with temperatures of 300? and 400? were designed The results show that after annealing at 300?,the transconductance peaks and current densities of the trench gate and oxygen plasma treatment device show a rebound,and the overall threshold voltage shows a negative drift,but the amplitude is small,about0.1V-0.2V.,with a certain degree of temperature stability.After annealing at 400?,the threshold voltage of the oxygen plasma treatment device has a significant negative shift range from 0.5V to 1.5V.The threshold voltages of conventional devices and their oxygen plasma processing devices are approaching the same,and the oxygen plasma processing device characteristics of the trench gate structure are still different from those of the non-oxygen plasma processing devices.