The influence of annealed ohmic contact metals on the electron mobility of a two dimensional electron gas （2DEG） is investigated on ungated AlGaN/GaN heterostructures and AlGaN/GaN heterostructure field effect trans...The influence of annealed ohmic contact metals on the electron mobility of a two dimensional electron gas （2DEG） is investigated on ungated AlGaN/GaN heterostructures and AlGaN/GaN heterostructure field effect transistors （AlGaN/GaN HFETs）. Current-voltage （I-V） characteristics for ungated AlGaN/GaN heterostructures and capacitance-voltage （C-V） characteristics for AlGaN/GaN HFETs are obtained, and the electron mobility for the ungated AlGaN/GaN heterostructure is calculated. It is found that the electron mobility of the 2DEG for the ungated AlGaN/GaN heterostructure is decreased by more than 50% compared with the electron mobility of Hall measurements. We propose that defects are introduced into the AlGaN barrier layer and the strain of the AlGaN barrier layer is changed during the annealing process of the source and drain, causing the decrease in the electron mobility.展开更多
Ni/Au Schottky contacts with thicknesses of either 50（？）/50（？） or 600（？）/2000（？） were deposited on strained Al_（0.3）Ga_（0.7）N/GaN heterostructures.Using the measured C-V curves and I-V characteristics ...Ni/Au Schottky contacts with thicknesses of either 50（？）/50（？） or 600（？）/2000（？） were deposited on strained Al_（0.3）Ga_（0.7）N/GaN heterostructures.Using the measured C-V curves and I-V characteristics at room temperature,the calculated density of the two-dimensional electron-gas（2DEG） of the 600（？）/2000（？） thick Ni/Au Schottky contact is about 9.13×10^（12） cm^（-2） and that of the 50（？）/50（？） thick Ni/Au Schottky contact is only about 4.77×10^（12） cm^（-2）.The saturated current increases from 60.88 to 86.34 mA at a bias of 20 V as the thickness of the Ni/Au Schottky contact increases from 50（？）/50（？） to 600 A/2000 A.By self-consistently solving Schrodinger＇s and Poisson＇s equations,the polarization charge sheet density of the two samples was calculated,and the calculated results show that the polarization in the AlGaN barrier layer for the thick Ni/Au Schottky contact is stronger than the thin one.Thus,we attribute the results to the increased biaxial tensile stress in the Al_（0.3）Ga_（0.7）N barrier layer induced by the 600（？）/2000（？） thick Ni/Au Schottky contact.展开更多
An Ni/Au Schottky contact on an AlGaN/GaN heterostructure has been prepared. By using the peak-conductance model, the threshold voltage and the series resistance of the AlGaN/GaN diode are simultaneously extracted fro...An Ni/Au Schottky contact on an AlGaN/GaN heterostructure has been prepared. By using the peak-conductance model, the threshold voltage and the series resistance of the AlGaN/GaN diode are simultaneously extracted from the conductance-voltage （G-V） curve and found to be in good agreement with the ones obtained by using the capacitance-voltage （C-V） curve integration and the plot of dV/d（ln I） versus current I. Thus, a method of directly and simultaneously extracting both the threshold voltage and the series resistance from the conductance-voltage curve for the AlGaN/GaN Schottky diode is developed.展开更多
The dispersion mechanism in Al0：27Ga0：73N/GaN heterostructure was investigated using frequencydependent capacitance and conductance measurements.It was found that the significant capacitance and conductance dispersi...The dispersion mechanism in Al0：27Ga0：73N/GaN heterostructure was investigated using frequencydependent capacitance and conductance measurements.It was found that the significant capacitance and conductance dispersion occurred primarily for measurement frequency beyond 100 kHz before the channel cutoff at the interface,suggesting that the vertical polarization electrical field under the gate metal should be closely related with the observed dispersive behavior.According to the Schottky-Read-Hall model,a traditional trapping mechanism cannot be used to explain our result.Instead,a piezoelectric polarization strain relaxation model was adopted to interpret the dispersion.By fitting the obtained capacitance data,the corresponding characteristic time and charge density were determined 10..8 s and 5.26 1012 cm..2 respectively,in good agreement with the conductance data and theoretical prediction.展开更多
Electron transport properties in AlGaN/GaN heterostructures with different Al-contents have been in-vestigated from room temperature up to 680 K. The temperature dependencies of electron mobility have been systematica...Electron transport properties in AlGaN/GaN heterostructures with different Al-contents have been in-vestigated from room temperature up to 680 K. The temperature dependencies of electron mobility have been systematically measured for the samples. The electron mobility at 680 K were measured as 154 and 182 cm2/V.s for Al0.15Ga0.85N/GaN and Al0.40Ga0.60N/GaN heterostructures,respectively. It was found that the electron mobility of low Al-content Al0.15Ga0.85N/GaN heterostructure was less than that of high Al-content Al0.40Ga0.60N/GaN heterostructure at high temperature of 680 K,which is different from that at room temperature. Detailed analysis showed that electron occupations in the first subband were 75% and 82% at 700 K for Al0.15Ga0.85N/GaN and Al0.40Ga0.60N/GaN heterostructures,respectively,and the two dimensional gas (2DEG) ratios in the whole electron system were 30% and near 60%,respectively. That indicated the 2DEG was better confined in the well,and was still dominant in the whole electron system for higher Al-content AlGaN/GaN heterostructure at 700 K,while lower one was not. Thus it had a higher electron mobility. So a higher Al-content AlGaN/GaN heterostructure is more suitable for high-temperature applications.展开更多
基金supported by the National Natural Science Foundation of China(No.10774090)the State Key Development Program for Basic Research of China(No.2007CB936602)
文摘The influence of annealed ohmic contact metals on the electron mobility of a two dimensional electron gas （2DEG） is investigated on ungated AlGaN/GaN heterostructures and AlGaN/GaN heterostructure field effect transistors （AlGaN/GaN HFETs）. Current-voltage （I-V） characteristics for ungated AlGaN/GaN heterostructures and capacitance-voltage （C-V） characteristics for AlGaN/GaN HFETs are obtained, and the electron mobility for the ungated AlGaN/GaN heterostructure is calculated. It is found that the electron mobility of the 2DEG for the ungated AlGaN/GaN heterostructure is decreased by more than 50% compared with the electron mobility of Hall measurements. We propose that defects are introduced into the AlGaN barrier layer and the strain of the AlGaN barrier layer is changed during the annealing process of the source and drain, causing the decrease in the electron mobility.
基金Project supported by the National Natural Science Foundation of China(No.10774090)the State Key Development Program for Basic Research of China(No.2007CB936602).
文摘Ni/Au Schottky contacts with thicknesses of either 50（？）/50（？） or 600（？）/2000（？） were deposited on strained Al_（0.3）Ga_（0.7）N/GaN heterostructures.Using the measured C-V curves and I-V characteristics at room temperature,the calculated density of the two-dimensional electron-gas（2DEG） of the 600（？）/2000（？） thick Ni/Au Schottky contact is about 9.13×10^（12） cm^（-2） and that of the 50（？）/50（？） thick Ni/Au Schottky contact is only about 4.77×10^（12） cm^（-2）.The saturated current increases from 60.88 to 86.34 mA at a bias of 20 V as the thickness of the Ni/Au Schottky contact increases from 50（？）/50（？） to 600 A/2000 A.By self-consistently solving Schrodinger＇s and Poisson＇s equations,the polarization charge sheet density of the two samples was calculated,and the calculated results show that the polarization in the AlGaN barrier layer for the thick Ni/Au Schottky contact is stronger than the thin one.Thus,we attribute the results to the increased biaxial tensile stress in the Al_（0.3）Ga_（0.7）N barrier layer induced by the 600（？）/2000（？） thick Ni/Au Schottky contact.
基金the National Natural Science Foundation of China(Grant Nos.60890192,60876009,and 11174182)the Foundation of Key Laboratory,China
文摘An Ni/Au Schottky contact on an AlGaN/GaN heterostructure has been prepared. By using the peak-conductance model, the threshold voltage and the series resistance of the AlGaN/GaN diode are simultaneously extracted from the conductance-voltage （G-V） curve and found to be in good agreement with the ones obtained by using the capacitance-voltage （C-V） curve integration and the plot of dV/d（ln I） versus current I. Thus, a method of directly and simultaneously extracting both the threshold voltage and the series resistance from the conductance-voltage curve for the AlGaN/GaN Schottky diode is developed.
基金Project supported by the Fundamental Research Funds for the Central Universities of China (Nos.JUSRP111A42,JUSRP211A37,JUSRP20914,JUSRP11230)the State Key Laboratory of ASIC & System,China (No.11KF003)the Natural Science Foundation of Jiangsu Province,China (No.BK2012110)
文摘The dispersion mechanism in Al0：27Ga0：73N/GaN heterostructure was investigated using frequencydependent capacitance and conductance measurements.It was found that the significant capacitance and conductance dispersion occurred primarily for measurement frequency beyond 100 kHz before the channel cutoff at the interface,suggesting that the vertical polarization electrical field under the gate metal should be closely related with the observed dispersive behavior.According to the Schottky-Read-Hall model,a traditional trapping mechanism cannot be used to explain our result.Instead,a piezoelectric polarization strain relaxation model was adopted to interpret the dispersion.By fitting the obtained capacitance data,the corresponding characteristic time and charge density were determined 10..8 s and 5.26 1012 cm..2 respectively,in good agreement with the conductance data and theoretical prediction.
文摘Electron transport properties in AlGaN/GaN heterostructures with different Al-contents have been in-vestigated from room temperature up to 680 K. The temperature dependencies of electron mobility have been systematically measured for the samples. The electron mobility at 680 K were measured as 154 and 182 cm2/V.s for Al0.15Ga0.85N/GaN and Al0.40Ga0.60N/GaN heterostructures,respectively. It was found that the electron mobility of low Al-content Al0.15Ga0.85N/GaN heterostructure was less than that of high Al-content Al0.40Ga0.60N/GaN heterostructure at high temperature of 680 K,which is different from that at room temperature. Detailed analysis showed that electron occupations in the first subband were 75% and 82% at 700 K for Al0.15Ga0.85N/GaN and Al0.40Ga0.60N/GaN heterostructures,respectively,and the two dimensional gas (2DEG) ratios in the whole electron system were 30% and near 60%,respectively. That indicated the 2DEG was better confined in the well,and was still dominant in the whole electron system for higher Al-content AlGaN/GaN heterostructure at 700 K,while lower one was not. Thus it had a higher electron mobility. So a higher Al-content AlGaN/GaN heterostructure is more suitable for high-temperature applications.
