In order to reduce deep level defects, the theory and process design of 4H-SiC homoepitaxial layer implanted by carbon ion are studied. With the Monte Carlo simulator TRIM, the ion implantation range, location of peak...In order to reduce deep level defects, the theory and process design of 4H-SiC homoepitaxial layer implanted by carbon ion are studied. With the Monte Carlo simulator TRIM, the ion implantation range, location of peak concentration and longitudinal straggling of carbon are calculated. The process for improving deep energy level in undoped 4H-SiC homoepitaxial layer by three times carbon ion-implantation is proposed, including implantation energy, dose, the SiO2 resist mask, annealing temperature, annealing time and annealing protection. The deep energy level in 4H-SiC material can be significantly improved by implantation of carbon atoms into a shallow surface layer. The damage of crystal lattice can be repaired well, and the carbon ions are effectively activated after 1 600 ℃ annealing, meanwhile, deep level defects are decreased.展开更多
Unintentionally doped 4H-SiC homoepitaxial layers grown by hot-wall chemical vapor deposition （HWCVD） have been studied using photoluminescence （PL） technique in the temperature range of 10 to 240 K. A broadband g...Unintentionally doped 4H-SiC homoepitaxial layers grown by hot-wall chemical vapor deposition （HWCVD） have been studied using photoluminescence （PL） technique in the temperature range of 10 to 240 K. A broadband green luminescence has been observed. Vacancies of carbon （Vc） are revealed by electron spin resonance （ESR） technique at 110 K. The results strongly suggest that the green band luminescence, as shallow donor-deep accepter emission, is attributed to the vacancies of C and the extended defects. The broadband green luminescence spectrum can be fitted by the two Gauss-type spectra using nonlinear optimization technique. It shows that the broad-band green luminescence originates from the combination of two independent radiative transitions. The centers of two energy levels are located 2.378 and 2.130 eV below the conduction band, respectively, and the ends of two energy levels are expanded and superimposed each other.展开更多
The influence of a deep-level-defect（DLD） band formed in a heavily Mg-doped GaN contact layer on the performance of Ni/Au contact to p-GaN is investigated. The thin heavily Mg-doped GaN（p^＋＋-GaN） contact layer w...The influence of a deep-level-defect（DLD） band formed in a heavily Mg-doped GaN contact layer on the performance of Ni/Au contact to p-GaN is investigated. The thin heavily Mg-doped GaN（p^＋＋-GaN） contact layer with DLD band can effectively improve the performance of Ni/Au ohmic contact to p-GaN. The temperature-dependent I–V measurement shows that the variable-range hopping（VRH） transportation through the DLD band plays a dominant role in the ohmic contact. The thickness and Mg/Ga flow ratio of p^＋＋-GaN contact layer have a significant effect on ohmic contact by controlling the Mg impurity doping and the formation of a proper DLD band. When the thickness of the p^＋＋-GaN contact layer is 25 nm thick and the Mg/Ga flow rate ratio is 10.29%, an ohmic contact with low specific contact resistivity of 6.97×10^-4Ω·cm^2 is achieved.展开更多
Electrically active defects in the phosphor-doped single-crystal silicon, induced by helium-ion irradiation under thermal annealing, have been investigated. Isothermal charge-sensitive deep-level transient spectroscop...Electrically active defects in the phosphor-doped single-crystal silicon, induced by helium-ion irradiation under thermal annealing, have been investigated. Isothermal charge-sensitive deep-level transient spectroscopy was employed to study the activation energy and capture cross-section of helium-induced defects in silicon samples. It was shown that the activation energy levels produced by helium-ion irradiation first increased with increasing annealing temperature, with the maximum value of the activation energy occurring at 873 K, and reduced with further increase of the annealing temperature. The energy levels of defects in the samples annealed at 873 and 1073 K are found to be located near the mid-forbidden energy gap level so that they can act as thermally stable carrier recombination centres.展开更多
Focusing on the low open circuit voltage(V_(OC))and fill factor(FF)in flexible Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells,indium(In)ions are introduced into the CZTSSe absorbers near Mo foils to modify the back interface...Focusing on the low open circuit voltage(V_(OC))and fill factor(FF)in flexible Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells,indium(In)ions are introduced into the CZTSSe absorbers near Mo foils to modify the back interface and passivate deep level defects in CZTSSe bulk concurrently for improving the performance of flexible device.The results show that In doping effectively inhibits the formation of secondary phase(Cu(S,Se)_(2))and VSndefects.Further studies demonstrate that the barrier height at the back interface is decreased and the deep level defects(Cu_(Sn)defects)in CZTSSe bulk are passivated.Moreover,the carrier concentration is increased and the V_(OC) deficit(V_(OC,def))is decreased significantly due to In doping.Finally,the flexible CZTSSe solar cell with 10.01%power conversion efficiency(PCE)has been obtained.The synergistic strategy of interface modification and bulk defects passivation through In incorporation provides a new thought for the fabrication of efficient flexible kesterite-based solar cells.展开更多
The deep-level defects of Cd Zn Te（CZT）crystals grown by the modified vertical Bridgman（MVB）method act as trapping centers or recombination centers in the band gap,which have significant effects on its electrical ...The deep-level defects of Cd Zn Te（CZT）crystals grown by the modified vertical Bridgman（MVB）method act as trapping centers or recombination centers in the band gap,which have significant effects on its electrical properties.The resistivity and electron mobility–lifetime product of high resistivity Cd（0.9）Zn（0.1）Te wafer marked CZT1 and low resistivity Cd（0.9）Zn（0.1）Te wafer marked CZT2 were tested respectively.Their deep-level defects were identified by thermally stimulated current（TSC）spectroscopy and thermoelectric effect spectroscopy（TEES）respectively.Then the trap-related parameters were characterized by the simultaneous multiple peak analysis（SIMPA）method.The deep donor level（EDD/dominating dark current was calculated by the relationship between dark current and temperature.The Fermi-level was characterized by current–voltage measurements of temperature dependence.The width of the band gap was characterized by ultraviolet-visible-infrared transmittance spectroscopy.The results show the traps concentration and capture cross section of CZT1 are lower than CZT2,so its electron mobility–lifetime product is greater than CZT2.The Fermi-level of CZT1 is closer to the middle gap than CZT2.The degree of Fermi-level pinned by EDDof CZT1 is larger than CZT2.It can be concluded that the resistivity of CZT crystals increases as the degree of Fermi-level pinned near the middle gap by the deep donor level enlarges.展开更多
基金Supported by the National Natural Science Foundation of China (No. 61006008)Xi'an Applied Materials Innovation Fund (No. XA-AM-200607)
文摘In order to reduce deep level defects, the theory and process design of 4H-SiC homoepitaxial layer implanted by carbon ion are studied. With the Monte Carlo simulator TRIM, the ion implantation range, location of peak concentration and longitudinal straggling of carbon are calculated. The process for improving deep energy level in undoped 4H-SiC homoepitaxial layer by three times carbon ion-implantation is proposed, including implantation energy, dose, the SiO2 resist mask, annealing temperature, annealing time and annealing protection. The deep energy level in 4H-SiC material can be significantly improved by implantation of carbon atoms into a shallow surface layer. The damage of crystal lattice can be repaired well, and the carbon ions are effectively activated after 1 600 ℃ annealing, meanwhile, deep level defects are decreased.
基金supported by the State Key Development Program for Basic Research of China (No. 51327020202)the Key Fund of the Ministryof Education of China (No. 106150)the Xi’an Applied Materials Innovation Fund (No. XA-AM-200607).
文摘Unintentionally doped 4H-SiC homoepitaxial layers grown by hot-wall chemical vapor deposition （HWCVD） have been studied using photoluminescence （PL） technique in the temperature range of 10 to 240 K. A broadband green luminescence has been observed. Vacancies of carbon （Vc） are revealed by electron spin resonance （ESR） technique at 110 K. The results strongly suggest that the green band luminescence, as shallow donor-deep accepter emission, is attributed to the vacancies of C and the extended defects. The broadband green luminescence spectrum can be fitted by the two Gauss-type spectra using nonlinear optimization technique. It shows that the broad-band green luminescence originates from the combination of two independent radiative transitions. The centers of two energy levels are located 2.378 and 2.130 eV below the conduction band, respectively, and the ends of two energy levels are expanded and superimposed each other.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61474110,61377020,61376089,61223005,and 61176126)the National Science Fund for Distinguished Young Scholars of China(Grant No.60925017)+1 种基金One Hundred Person Project of the Chinese Academy of Sciencesthe Basic Research Project of Jiangsu Province,China(Grant No.BK20130362)
文摘The influence of a deep-level-defect（DLD） band formed in a heavily Mg-doped GaN contact layer on the performance of Ni/Au contact to p-GaN is investigated. The thin heavily Mg-doped GaN（p^＋＋-GaN） contact layer with DLD band can effectively improve the performance of Ni/Au ohmic contact to p-GaN. The temperature-dependent I–V measurement shows that the variable-range hopping（VRH） transportation through the DLD band plays a dominant role in the ohmic contact. The thickness and Mg/Ga flow ratio of p^＋＋-GaN contact layer have a significant effect on ohmic contact by controlling the Mg impurity doping and the formation of a proper DLD band. When the thickness of the p^＋＋-GaN contact layer is 25 nm thick and the Mg/Ga flow rate ratio is 10.29%, an ohmic contact with low specific contact resistivity of 6.97×10^-4Ω·cm^2 is achieved.
基金Project supported by the National Natural Science Foundation of China (Grant No 10575124)
文摘Electrically active defects in the phosphor-doped single-crystal silicon, induced by helium-ion irradiation under thermal annealing, have been investigated. Isothermal charge-sensitive deep-level transient spectroscopy was employed to study the activation energy and capture cross-section of helium-induced defects in silicon samples. It was shown that the activation energy levels produced by helium-ion irradiation first increased with increasing annealing temperature, with the maximum value of the activation energy occurring at 873 K, and reduced with further increase of the annealing temperature. The energy levels of defects in the samples annealed at 873 and 1073 K are found to be located near the mid-forbidden energy gap level so that they can act as thermally stable carrier recombination centres.
基金supported by the National Natural Science Foundation of China(62074037)the Science and Technology Department of Fujian Province(2020I0006)the Fujian Science&Technology Innovation Laboratory for Optoelectronic Information of China(2021ZZ124)。
文摘Focusing on the low open circuit voltage(V_(OC))and fill factor(FF)in flexible Cu_(2)ZnSn(S,Se)_(4)(CZTSSe)solar cells,indium(In)ions are introduced into the CZTSSe absorbers near Mo foils to modify the back interface and passivate deep level defects in CZTSSe bulk concurrently for improving the performance of flexible device.The results show that In doping effectively inhibits the formation of secondary phase(Cu(S,Se)_(2))and VSndefects.Further studies demonstrate that the barrier height at the back interface is decreased and the deep level defects(Cu_(Sn)defects)in CZTSSe bulk are passivated.Moreover,the carrier concentration is increased and the V_(OC) deficit(V_(OC,def))is decreased significantly due to In doping.Finally,the flexible CZTSSe solar cell with 10.01%power conversion efficiency(PCE)has been obtained.The synergistic strategy of interface modification and bulk defects passivation through In incorporation provides a new thought for the fabrication of efficient flexible kesterite-based solar cells.
基金supported by the National Natural Science Foundation of China(No.51502234)the Scientific Research Plan Projects of Shaanxi Provincial Department of Education of China(No.15JS040)
文摘The deep-level defects of Cd Zn Te（CZT）crystals grown by the modified vertical Bridgman（MVB）method act as trapping centers or recombination centers in the band gap,which have significant effects on its electrical properties.The resistivity and electron mobility–lifetime product of high resistivity Cd（0.9）Zn（0.1）Te wafer marked CZT1 and low resistivity Cd（0.9）Zn（0.1）Te wafer marked CZT2 were tested respectively.Their deep-level defects were identified by thermally stimulated current（TSC）spectroscopy and thermoelectric effect spectroscopy（TEES）respectively.Then the trap-related parameters were characterized by the simultaneous multiple peak analysis（SIMPA）method.The deep donor level（EDD/dominating dark current was calculated by the relationship between dark current and temperature.The Fermi-level was characterized by current–voltage measurements of temperature dependence.The width of the band gap was characterized by ultraviolet-visible-infrared transmittance spectroscopy.The results show the traps concentration and capture cross section of CZT1 are lower than CZT2,so its electron mobility–lifetime product is greater than CZT2.The Fermi-level of CZT1 is closer to the middle gap than CZT2.The degree of Fermi-level pinned by EDDof CZT1 is larger than CZT2.It can be concluded that the resistivity of CZT crystals increases as the degree of Fermi-level pinned near the middle gap by the deep donor level enlarges.
