The electrical characteristics of graphene Schottky contacts formed on undoped GaN semiconductors were investigated. Excellent rectifying behavior with a rectification ratio of -10^7 at ±2 V and a low reverse lea...The electrical characteristics of graphene Schottky contacts formed on undoped GaN semiconductors were investigated. Excellent rectifying behavior with a rectification ratio of -10^7 at ±2 V and a low reverse leakage current of 1.0 × 10^-8 A/cm^2 at -5 V were observed. The Schottky barrier heights, as determined by the thermionic emission model Richardson plots, and barrier inhomogeneity model, were 0.90, 0.72, and 1.24 ± 0.13 eV, respectively. Despite the predicted low barrier height of -0.4 eV at the graphene-GaN interface, the formation of excellent rectifying characteristics with much larger barrier heights is attributed to the presence of a large number of surface states （1.2 x 1013 states/cm2/eV） and the internal spontaneous polarization field of GaN, resulted in a significant upward surface band bending or a bare surface barrier height as high as of 2.9 eV. Using the S parameter of 0.48 （measured from the work function dependence of Schottky barrier height） and the mean barrier height of 1.24 eV, the work function of graphene in the Au/graphene/GaN stack could be approximately estimated to be as low as 3.5 eV. The obtained results indicate that graphene is a promising candidate for use as a Schottky rectifier in GaN semiconductors with n-type conductivity.展开更多
The dielectric functions of GaN for the temperature and frequency ranges of 10–300 K and 0.3–1 THz are obtained using terahertz time-domain spectroscopy.It is found that there are oscillations of the dielectric func...The dielectric functions of GaN for the temperature and frequency ranges of 10–300 K and 0.3–1 THz are obtained using terahertz time-domain spectroscopy.It is found that there are oscillations of the dielectric functions at various temperatures.Physically,the oscillation behavior is attributed to the resonance states of the point defects in the material.Furthermore,the dielectric functions are well fitted by the combination of the simple Drude model together with the classical damped oscillator model.According to the values of the fitting parameters,the concentration and electron lifetime of the point defects for various temperatures are determined,and the temperature dependences of them are in accordance with the previously reported result.Therefore,terahertz time-domain spectroscopy can be considered as a promising technique for investigating the relevant characteristics of the point defects in semiconductor materials.展开更多
Though GaN nanoribbons （GaNNRs） with H atoms terminating both edges are nonmagnetic semiconductors, the extra dangling bond bands around the Fermi level lead to a transition from semiconducting to metallic, except f...Though GaN nanoribbons （GaNNRs） with H atoms terminating both edges are nonmagnetic semiconductors, the extra dangling bond bands around the Fermi level lead to a transition from semiconducting to metallic, except for the armchair edge GaNNRs （AGaNNRs） with bare N and Ga edges, which are still nonmagnetic semiconductors due to the strong coupling of the dangling bonds of dimeric N and Ga atoms at the same edge. The larger difference in the charge density （pUp_pdown） for edge bare N atoms and decaying for N sub-lattices away from the edge, as well as the smaller difference in the charge density for edge bare Ga atoms and without decaying for Ga sub-lattices away from the edge is consistent with the magnetic moment of a GaNNR with bare N edge being larger than that of a GaNNR with bare Ga edge. The magnetic moment of a zigzag edge GaNNR （ZGaNNR） with bare N （Ga） edge has nearly half the value of the magnetic moment of a AGaNNR with bare N （Ga） edge. Such a relationship also exists in the number of extra dangling bond states appearing around the Fermi level in the band structures. For ZGaNNRs, the magnetic moment of bare N and Ga edges is larger than either bare N edge or bare Ga edge, but smaller than their sum, implying that there exists an interaction between the dangling bonds at both edges of bare N and Ga edges.展开更多
文摘The electrical characteristics of graphene Schottky contacts formed on undoped GaN semiconductors were investigated. Excellent rectifying behavior with a rectification ratio of -10^7 at ±2 V and a low reverse leakage current of 1.0 × 10^-8 A/cm^2 at -5 V were observed. The Schottky barrier heights, as determined by the thermionic emission model Richardson plots, and barrier inhomogeneity model, were 0.90, 0.72, and 1.24 ± 0.13 eV, respectively. Despite the predicted low barrier height of -0.4 eV at the graphene-GaN interface, the formation of excellent rectifying characteristics with much larger barrier heights is attributed to the presence of a large number of surface states （1.2 x 1013 states/cm2/eV） and the internal spontaneous polarization field of GaN, resulted in a significant upward surface band bending or a bare surface barrier height as high as of 2.9 eV. Using the S parameter of 0.48 （measured from the work function dependence of Schottky barrier height） and the mean barrier height of 1.24 eV, the work function of graphene in the Au/graphene/GaN stack could be approximately estimated to be as low as 3.5 eV. The obtained results indicate that graphene is a promising candidate for use as a Schottky rectifier in GaN semiconductors with n-type conductivity.
基金supported by the Special Funds for Major State Basic Research Project (Grant No. 2011CB301900)the 973 project of the Ministry of Science and Technology of China (Grant No. 2011CBA00107)+4 种基金the Hi-tech Research Project (Grant No. 2011AA03A103)the National Natural Science Foundation of China (Grant Nos. 60990311, 60820106003, 60906025, 60936004, 61176063, 61071009, and 61027008)the Specialized Research Fund for the Doctoral Program of Higher Education (Grant No. 20090091110040)the Natural Science of Foundation of Jiangsu province (Grant Nos. BK2011010, BK2010385, and BK2010178)the Fok Ying-Tong Education Foundation (Grant No. 122028)
文摘The dielectric functions of GaN for the temperature and frequency ranges of 10–300 K and 0.3–1 THz are obtained using terahertz time-domain spectroscopy.It is found that there are oscillations of the dielectric functions at various temperatures.Physically,the oscillation behavior is attributed to the resonance states of the point defects in the material.Furthermore,the dielectric functions are well fitted by the combination of the simple Drude model together with the classical damped oscillator model.According to the values of the fitting parameters,the concentration and electron lifetime of the point defects for various temperatures are determined,and the temperature dependences of them are in accordance with the previously reported result.Therefore,terahertz time-domain spectroscopy can be considered as a promising technique for investigating the relevant characteristics of the point defects in semiconductor materials.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51071098 and 11104175)the State Key Development for Basic Research of China (Grant No. 2010CB631002)
文摘Though GaN nanoribbons （GaNNRs） with H atoms terminating both edges are nonmagnetic semiconductors, the extra dangling bond bands around the Fermi level lead to a transition from semiconducting to metallic, except for the armchair edge GaNNRs （AGaNNRs） with bare N and Ga edges, which are still nonmagnetic semiconductors due to the strong coupling of the dangling bonds of dimeric N and Ga atoms at the same edge. The larger difference in the charge density （pUp_pdown） for edge bare N atoms and decaying for N sub-lattices away from the edge, as well as the smaller difference in the charge density for edge bare Ga atoms and without decaying for Ga sub-lattices away from the edge is consistent with the magnetic moment of a GaNNR with bare N edge being larger than that of a GaNNR with bare Ga edge. The magnetic moment of a zigzag edge GaNNR （ZGaNNR） with bare N （Ga） edge has nearly half the value of the magnetic moment of a AGaNNR with bare N （Ga） edge. Such a relationship also exists in the number of extra dangling bond states appearing around the Fermi level in the band structures. For ZGaNNRs, the magnetic moment of bare N and Ga edges is larger than either bare N edge or bare Ga edge, but smaller than their sum, implying that there exists an interaction between the dangling bonds at both edges of bare N and Ga edges.
