In this work, the effects of GaN channel traps and temperature on the performance of AlGaN/AlN/GaN/AlGaN high electron mobility transistors(HEMTs) on Si(111) substrate, were investigated. 2 D simulations carried out u...In this work, the effects of GaN channel traps and temperature on the performance of AlGaN/AlN/GaN/AlGaN high electron mobility transistors(HEMTs) on Si(111) substrate, were investigated. 2 D simulations carried out using the Silvaco TCAD simulator tool for different drain and gate voltages showed that acceptor-like traps in the channel have a significant influence on the DC and RF characteristics. It was found that deeper acceptors below the conduction band with larger concentration have a more pronounced effect on the transistor performance. Meanwhile, the donor-like traps show no influence. Pulsing the device with different pulse widths and bias conditions, as well as increasing temperature, showed that the traps are more ionized when the pulse is wider or the temperature is higher, which can degrade the drain current and thus the DC characteristics of the transistor. Passivation of the transistor has also a beneficial effect on performance.展开更多
AlGaN/GaN high electron mobility transistors （HEMTs） grown on Fe-modulation-doped （MD） and unintentionally doped （UID） GaN buffer layers are investigated and compared. Highly resistive GaN buffers （10^9Ω·...AlGaN/GaN high electron mobility transistors （HEMTs） grown on Fe-modulation-doped （MD） and unintentionally doped （UID） GaN buffer layers are investigated and compared. Highly resistive GaN buffers （10^9Ω·cm） are induced by individual mechanisms for the electron traps＇ formation： the Fe MD buffer （sample A） and the UID buffer with high density of edge-type dislocations （7.24×10^9cm^-2, sample B）. The 300K Hall test indicates that the mobility of sample A with Fe doping （2503cm^2V^-1s^-1） is much higher than sample B （1926cm^2V^-1s^-1） due to the decreased scattering effect on the two-dimensional electron gas. HEMT devices are fabricated on the two samples and pulsed I–V measurements are conducted. Device A shows better gate pinch-off characteristics and a higher threshold voltage （-2.63V） compared with device B （-3.71V）. Lower gate leakage current ｜IGS｜ of device A （3.32×10^-7A） is present compared with that of device B （8.29×10^-7A）. When the off-state quiescent points Q_2 （V GQ2=-8V, V DQ2=0V） are on, V th hardly shifts for device A while device B shows ＋0.21V positive threshold voltage shift, resulting from the existence of electron traps associated with the dislocations in the UID-GaN buffer layer under the gate. Under pulsed I–V and transconductance G m–V GS measurement, the device with the Fe MD-doped buffer shows more potential in improving reliability upon off-state stress.展开更多
It was reported by Shen et al that the two-dimensional electron gas （2DEG） in an AlGaN/AlN/GaN structure showed high density and improved mobility compared with an AlGaN/GaN structure, but the potential of the AlGaN...It was reported by Shen et al that the two-dimensional electron gas （2DEG） in an AlGaN/AlN/GaN structure showed high density and improved mobility compared with an AlGaN/GaN structure, but the potential of the AlGaN/AlN/GaN structure needs further exploration. By the self-consistent solving of one-dimensional Schroedinger- Poisson equations, theoretical investigation is carried out about the effects of donor density （0-1×10^19 cm^-3） and temperature （50-500 K） on the electron systems in the AlGaN/AlN/GaN and AlGaN/GaN structures. It is found that in the former structure, since the effective △Ec is larger, the efficiency with which the 2DEG absorbs the electrons originating from donor ionization is higher, the resistance to parallel conduction is stronger, and the deterioration of 2DEG mobility is slower as the donor density rises. When temperature rises, the three-dimensional properties of the whole electron system become prominent for both of the structures, but the stability of 2DEG is higher in the former structure, which is also ascribed to the larger effective △Ec. The Capacitance-Voltage （C - V） carrier density profiles at different temperatures are measured for two Schottky diodes on the considered heterostructure samples separately, showing obviously different 2DEG densities. And the temperature-dependent tendency of the experimental curves agrees well with our calculations.展开更多
This paper deduces the expression of the Schottky contact capacitance of AlGaN/A1N/GaN high electron mobility transistors （HEMTs）, which will help to understand the electron depleting process. Some material paramete...This paper deduces the expression of the Schottky contact capacitance of AlGaN/A1N/GaN high electron mobility transistors （HEMTs）, which will help to understand the electron depleting process. Some material parameters related with capacitance-voltage profiling are given in the expression. Detailed analysis of the forward-biased capacitance has been carried on. The gate capacitance of undoped AlGaN/AlN/GaN HEMT will fall under forward bias. If a rising profile is obviously observed, the donor-like impurity or trap is possibly introduced in the barrier.展开更多
Rectangular Schottky drain AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate contact areas and conventional AlGaN/AlN/GaN HFETs as control were both fabricated with same size. It was...Rectangular Schottky drain AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate contact areas and conventional AlGaN/AlN/GaN HFETs as control were both fabricated with same size. It was found there is a significant difference between Schottky drain AlGaN/AlN/GaN HFETs and the control group both in drain series resistance and in two-dimensional electron gas （2DEG） electron mobility in the gate–drain channel. We attribute this to the different influence of Ohmic drain contacts and Schottky drain contacts on the strained AlGaN barrier layer. For conventional AlGaN/AlN/GaN HFETs, annealing drain Ohmic contacts gives rise to a strain variation in the AlGaN barrier layer between the gate contacts and the drain contacts, and results in strong polarization Coulomb field scattering in this region. In Schottky drain AlGaN/AlN/GaN HFETs, the strain in the AlGaN barrier layer is distributed more regularly.展开更多
We simulate the current-voltage （I-V） characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate lengths using the quasi-two-dimensional （quasi-2D） model. The calculati...We simulate the current-voltage （I-V） characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate lengths using the quasi-two-dimensional （quasi-2D） model. The calculation results obtained using the modified mobility model are found to accord well with the experimental data. By analyzing the variation of the electron mobility for the two-dimensional electron gas （213EG） with the electric field in the linear region of the AlGaN/AlN/GaN HFET I-V output characteristics, it is found that the polarization Coulomb field scattering still plays an important role in the electron mobility of AlGaN/AlN/GaN HFETs at the higher drain voltage and channel electric field. As drain voltage and channel electric field increase, the 2DEG density reduces and the polarization Coulomb field scattering increases, as a result, the 2DEG electron mobility decreases.展开更多
Rectangular AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） were fabricated, and the gate and the source of the HFETs consisted of AlGaN/AlN/CaN Schottky barrier diodes （SBDs）. Based on the measured...Rectangular AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） were fabricated, and the gate and the source of the HFETs consisted of AlGaN/AlN/CaN Schottky barrier diodes （SBDs）. Based on the measured forward current-voltage and the capacitance-voltage characteristics of the AlGaN/AlN/GaN SBDs, the series resistance under the Schottky contacts （Rs） was calculated using the method of power consumption, which has been proved to be valid. Finally, the method of power consumption for calculating RS was successfully used to study the two-dimensional electron gas electron mobility for a series of circular AlGaN/AlN/GaN SBDs. It is shown that the series resistance under the Schottky contacts cannot be neglected and is important for analysing and characterizing the AIGaN/AIN/GaN SBDs and the AlGaN/AlN/GaN HFETs.展开更多
Direct-current transfer characteristics of （InGaN）/A1GaN/A1N/GaN heterojunction field effect transistors （HFETs） are presented. A drain current plateau （IDs = 32.0 mA/mm） for Vcs swept from ＋0.7 V to -0. 6 V is...Direct-current transfer characteristics of （InGaN）/A1GaN/A1N/GaN heterojunction field effect transistors （HFETs） are presented. A drain current plateau （IDs = 32.0 mA/mm） for Vcs swept from ＋0.7 V to -0. 6 V is present in the transfer characteristics of InGaN/AIGaN/AIN/GaN HFETs. The theoretical calculation shows the coexistence of two-dimensional electron gas （2DEG） and two-dimensional hole gas （2DHG） in InGaN/AIGaN/A1N/GaN heterostructures, and the screening effect of 2DHG to the 2DEG in the conduction channel can explain this current plateau. Moreover, the current plateau shows the time-dependent behavior when IDs Vcs scans repeated are conducted. The obtained insight provides indication for the design in the fabrication of GaN-based super HFETs.展开更多
In this study rectangular AlGaN/AlN/GaN heterostructure field-effect transistors(HFETs) with 22-nm and 12-nm AlGaN barrier layers are fabricated, respectively. Using the measured capacitance–voltage and current–volt...In this study rectangular AlGaN/AlN/GaN heterostructure field-effect transistors(HFETs) with 22-nm and 12-nm AlGaN barrier layers are fabricated, respectively. Using the measured capacitance–voltage and current–voltage characteristics of the prepared devices with different Schottky areas, it is found that after processing the device, the polarization Coulomb field(PCF) scattering is induced and has an important influence on the two-dimensional electron gas electron mobility.Moreover, the influence of PCF scattering on the electron mobility is enhanced by reducing the AlGaN barrier thickness.This leads to the quite different variation of the electron mobility with gate bias when compared with the AlGaN barrier thickness. This mainly happens because the thinner AlGaN barrier layer suffers from a much stronger electrical field when applying a gate bias, which gives rise to a stronger converse piezoelectric effect.展开更多
Using measured capacitance-voltage curves and current-voltage characteristics for the AlGaN/AlN/GaN heterostructure field-effect transistors with different gate lengths and drain-to-source distances, the influence of ...Using measured capacitance-voltage curves and current-voltage characteristics for the AlGaN/AlN/GaN heterostructure field-effect transistors with different gate lengths and drain-to-source distances, the influence of drain bias on the electron mobility is investigated. It is found that below the knee voltage the longitudinal optical （LO） phonon scattering and interface roughness scattering are dominant for the sample with a large ratio of gate length to drain-to-source distance （here 4/5）, and the polarization Coulomb field scattering is dominant for the sample with a small ratio （here 1/5）. However, the above polarization Coulomb field scattering is weakened in the sample with a small drain-to-source distance （here 20 μm） compared with the one with a large distance （here 100 μm）. This is due to the induced strain in the AlGaN layer caused by the drain bias.展开更多
The parasitic source resistance（RS） of AlGaN/AlN/GaN heterostructure field-effect transistors（HFETs） is studied in the temperature range 300–500 K. By using the measured RSand both capacitance–voltage（C–V） an...The parasitic source resistance（RS） of AlGaN/AlN/GaN heterostructure field-effect transistors（HFETs） is studied in the temperature range 300–500 K. By using the measured RSand both capacitance–voltage（C–V） and current–voltage（I–V） characteristics for the fabricated device at 300, 350, 400, 450, and 500 K, it is found that the polarization Coulomb field（PCF） scattering exhibits a significant impact on RSat the above-mentioned different temperatures. Furthermore, in the AlGaN/AlN/GaN HFETs, the interaction between the additional positive polarization charges underneath the gate contact and the additional negative polarization charges near the source Ohmic contact, which is related to the PCF scattering, is verified during the variable-temperature study of RS.展开更多
In this letter,high power density AlGaN/GaN high electron-mobility transistors(HEMTs)on a freestanding GaN substrate are reported.An asymmetricΓ-shaped 500-nm gate with a field plate of 650 nm is introduced to improv...In this letter,high power density AlGaN/GaN high electron-mobility transistors(HEMTs)on a freestanding GaN substrate are reported.An asymmetricΓ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance.The breakdown voltage(BV)is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92μm.A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V.The maximum oscillation frequency(f_(max))and unity current gain cut-off frequency(f_(t))of the AlGaN/GaN HEMTs exceed 30 and 20 GHz,respectively.The results demonstrate the potential of AlGaN/GaN HEMTs on freestanding GaN substrates for microwave power applications.展开更多
文摘In this work, the effects of GaN channel traps and temperature on the performance of AlGaN/AlN/GaN/AlGaN high electron mobility transistors(HEMTs) on Si(111) substrate, were investigated. 2 D simulations carried out using the Silvaco TCAD simulator tool for different drain and gate voltages showed that acceptor-like traps in the channel have a significant influence on the DC and RF characteristics. It was found that deeper acceptors below the conduction band with larger concentration have a more pronounced effect on the transistor performance. Meanwhile, the donor-like traps show no influence. Pulsing the device with different pulse widths and bias conditions, as well as increasing temperature, showed that the traps are more ionized when the pulse is wider or the temperature is higher, which can degrade the drain current and thus the DC characteristics of the transistor. Passivation of the transistor has also a beneficial effect on performance.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61204017 and 61334002the National Basic Research Program of Chinathe National Science and Technology Major Project of China
文摘AlGaN/GaN high electron mobility transistors （HEMTs） grown on Fe-modulation-doped （MD） and unintentionally doped （UID） GaN buffer layers are investigated and compared. Highly resistive GaN buffers （10^9Ω·cm） are induced by individual mechanisms for the electron traps＇ formation： the Fe MD buffer （sample A） and the UID buffer with high density of edge-type dislocations （7.24×10^9cm^-2, sample B）. The 300K Hall test indicates that the mobility of sample A with Fe doping （2503cm^2V^-1s^-1） is much higher than sample B （1926cm^2V^-1s^-1） due to the decreased scattering effect on the two-dimensional electron gas. HEMT devices are fabricated on the two samples and pulsed I–V measurements are conducted. Device A shows better gate pinch-off characteristics and a higher threshold voltage （-2.63V） compared with device B （-3.71V）. Lower gate leakage current ｜IGS｜ of device A （3.32×10^-7A） is present compared with that of device B （8.29×10^-7A）. When the off-state quiescent points Q_2 （V GQ2=-8V, V DQ2=0V） are on, V th hardly shifts for device A while device B shows ＋0.21V positive threshold voltage shift, resulting from the existence of electron traps associated with the dislocations in the UID-GaN buffer layer under the gate. Under pulsed I–V and transconductance G m–V GS measurement, the device with the Fe MD-doped buffer shows more potential in improving reliability upon off-state stress.
文摘It was reported by Shen et al that the two-dimensional electron gas （2DEG） in an AlGaN/AlN/GaN structure showed high density and improved mobility compared with an AlGaN/GaN structure, but the potential of the AlGaN/AlN/GaN structure needs further exploration. By the self-consistent solving of one-dimensional Schroedinger- Poisson equations, theoretical investigation is carried out about the effects of donor density （0-1×10^19 cm^-3） and temperature （50-500 K） on the electron systems in the AlGaN/AlN/GaN and AlGaN/GaN structures. It is found that in the former structure, since the effective △Ec is larger, the efficiency with which the 2DEG absorbs the electrons originating from donor ionization is higher, the resistance to parallel conduction is stronger, and the deterioration of 2DEG mobility is slower as the donor density rises. When temperature rises, the three-dimensional properties of the whole electron system become prominent for both of the structures, but the stability of 2DEG is higher in the former structure, which is also ascribed to the larger effective △Ec. The Capacitance-Voltage （C - V） carrier density profiles at different temperatures are measured for two Schottky diodes on the considered heterostructure samples separately, showing obviously different 2DEG densities. And the temperature-dependent tendency of the experimental curves agrees well with our calculations.
基金supported by the National Basic Research Program (973) of China (Grant No.2010CB327500)the National Natural Science Foundation of China (Grant Nos.60976059 and 60890191)
文摘This paper deduces the expression of the Schottky contact capacitance of AlGaN/A1N/GaN high electron mobility transistors （HEMTs）, which will help to understand the electron depleting process. Some material parameters related with capacitance-voltage profiling are given in the expression. Detailed analysis of the forward-biased capacitance has been carried on. The gate capacitance of undoped AlGaN/AlN/GaN HEMT will fall under forward bias. If a rising profile is obviously observed, the donor-like impurity or trap is possibly introduced in the barrier.
基金Project supported by the National Natural Science Foundation of China (Grant No. 11174182)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20110131110005)
文摘Rectangular Schottky drain AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate contact areas and conventional AlGaN/AlN/GaN HFETs as control were both fabricated with same size. It was found there is a significant difference between Schottky drain AlGaN/AlN/GaN HFETs and the control group both in drain series resistance and in two-dimensional electron gas （2DEG） electron mobility in the gate–drain channel. We attribute this to the different influence of Ohmic drain contacts and Schottky drain contacts on the strained AlGaN barrier layer. For conventional AlGaN/AlN/GaN HFETs, annealing drain Ohmic contacts gives rise to a strain variation in the AlGaN barrier layer between the gate contacts and the drain contacts, and results in strong polarization Coulomb field scattering in this region. In Schottky drain AlGaN/AlN/GaN HFETs, the strain in the AlGaN barrier layer is distributed more regularly.
基金supported by the National Natural Science Foundation of China (Grant No. 11174182)the Specialized Research Fund for the Doctoral Program of Higher Education,China (Grant No. 20110131110005)
文摘We simulate the current-voltage （I-V） characteristics of AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） with different gate lengths using the quasi-two-dimensional （quasi-2D） model. The calculation results obtained using the modified mobility model are found to accord well with the experimental data. By analyzing the variation of the electron mobility for the two-dimensional electron gas （213EG） with the electric field in the linear region of the AlGaN/AlN/GaN HFET I-V output characteristics, it is found that the polarization Coulomb field scattering still plays an important role in the electron mobility of AlGaN/AlN/GaN HFETs at the higher drain voltage and channel electric field. As drain voltage and channel electric field increase, the 2DEG density reduces and the polarization Coulomb field scattering increases, as a result, the 2DEG electron mobility decreases.
基金Project supported by the National Natural Science Foundation of China(Grant No.10774090)the National Basic Research Program of China(Grant No.2007CB936602)
文摘Rectangular AlGaN/AlN/GaN heterostructure field-effect transistors （HFETs） were fabricated, and the gate and the source of the HFETs consisted of AlGaN/AlN/CaN Schottky barrier diodes （SBDs）. Based on the measured forward current-voltage and the capacitance-voltage characteristics of the AlGaN/AlN/GaN SBDs, the series resistance under the Schottky contacts （Rs） was calculated using the method of power consumption, which has been proved to be valid. Finally, the method of power consumption for calculating RS was successfully used to study the two-dimensional electron gas electron mobility for a series of circular AlGaN/AlN/GaN SBDs. It is shown that the series resistance under the Schottky contacts cannot be neglected and is important for analysing and characterizing the AIGaN/AIN/GaN SBDs and the AlGaN/AlN/GaN HFETs.
基金Supported by the Knowledge Innovation Project of the Chinese Academy of Sciencesthe National Natural Science Foundation of China under Grant Nos 61204017 and 61334002+1 种基金the National Basic Research Program of Chinathe National Science and Technology Major Project of China
文摘Direct-current transfer characteristics of （InGaN）/A1GaN/A1N/GaN heterojunction field effect transistors （HFETs） are presented. A drain current plateau （IDs = 32.0 mA/mm） for Vcs swept from ＋0.7 V to -0. 6 V is present in the transfer characteristics of InGaN/AIGaN/AIN/GaN HFETs. The theoretical calculation shows the coexistence of two-dimensional electron gas （2DEG） and two-dimensional hole gas （2DHG） in InGaN/AIGaN/A1N/GaN heterostructures, and the screening effect of 2DHG to the 2DEG in the conduction channel can explain this current plateau. Moreover, the current plateau shows the time-dependent behavior when IDs Vcs scans repeated are conducted. The obtained insight provides indication for the design in the fabrication of GaN-based super HFETs.
基金supported by the National Natural Science Foundation of China(Grant Nos.61306113 and11174182)
文摘In this study rectangular AlGaN/AlN/GaN heterostructure field-effect transistors(HFETs) with 22-nm and 12-nm AlGaN barrier layers are fabricated, respectively. Using the measured capacitance–voltage and current–voltage characteristics of the prepared devices with different Schottky areas, it is found that after processing the device, the polarization Coulomb field(PCF) scattering is induced and has an important influence on the two-dimensional electron gas electron mobility.Moreover, the influence of PCF scattering on the electron mobility is enhanced by reducing the AlGaN barrier thickness.This leads to the quite different variation of the electron mobility with gate bias when compared with the AlGaN barrier thickness. This mainly happens because the thinner AlGaN barrier layer suffers from a much stronger electrical field when applying a gate bias, which gives rise to a stronger converse piezoelectric effect.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11174182 and 10774090)
文摘Using measured capacitance-voltage curves and current-voltage characteristics for the AlGaN/AlN/GaN heterostructure field-effect transistors with different gate lengths and drain-to-source distances, the influence of drain bias on the electron mobility is investigated. It is found that below the knee voltage the longitudinal optical （LO） phonon scattering and interface roughness scattering are dominant for the sample with a large ratio of gate length to drain-to-source distance （here 4/5）, and the polarization Coulomb field scattering is dominant for the sample with a small ratio （here 1/5）. However, the above polarization Coulomb field scattering is weakened in the sample with a small drain-to-source distance （here 20 μm） compared with the one with a large distance （here 100 μm）. This is due to the induced strain in the AlGaN layer caused by the drain bias.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11174182,11574182,and 61306113)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20110131110005)
文摘The parasitic source resistance（RS） of AlGaN/AlN/GaN heterostructure field-effect transistors（HFETs） is studied in the temperature range 300–500 K. By using the measured RSand both capacitance–voltage（C–V） and current–voltage（I–V） characteristics for the fabricated device at 300, 350, 400, 450, and 500 K, it is found that the polarization Coulomb field（PCF） scattering exhibits a significant impact on RSat the above-mentioned different temperatures. Furthermore, in the AlGaN/AlN/GaN HFETs, the interaction between the additional positive polarization charges underneath the gate contact and the additional negative polarization charges near the source Ohmic contact, which is related to the PCF scattering, is verified during the variable-temperature study of RS.
文摘In this letter,high power density AlGaN/GaN high electron-mobility transistors(HEMTs)on a freestanding GaN substrate are reported.An asymmetricΓ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance.The breakdown voltage(BV)is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92μm.A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V.The maximum oscillation frequency(f_(max))and unity current gain cut-off frequency(f_(t))of the AlGaN/GaN HEMTs exceed 30 and 20 GHz,respectively.The results demonstrate the potential of AlGaN/GaN HEMTs on freestanding GaN substrates for microwave power applications.
