Papers by Keyword: Ionization Energy

Abstract: Aluminum implanted 4H-SiC often shows an unexpected increase of the free hole density at elevated temperatures in Hall Effect measurements. Here we show that this phenomenon cannot solely be traced down to the Hall scattering factor and the presence of excited acceptor states. It is necessary to assume an additional defect center in the lower half of the band gap with ionization energies higher than that of aluminum to explain this behavior. Therefore, we investigated ion-implanted square van-der-Pauw samples with Hall Effect and complementary SIMS measurements. An analysis of the data using the neutrality equation reveals compensation ratios of 20 % to 90 %, depending on the aluminum concentration and the concentration of the deep defect center of up to 50 % of the doping.

Abstract: In this work, we analyze compensating defects which are formed after implantation of aluminum (Al) into n-type 4H-SiC epitaxial layers and subsequent thermal annealing. These defects reduce the expected free charge carrier density by 84% for a low doped layer with [Al]_impl ≈ 9ž·10¹⁶ cm^-3 and by 27 % for a high doped layer with [Al]_impl ≈ 2·ž10¹⁹ cm^-3. Furthermore, an electrical activation ratio of implanted aluminum ions of 100 % is calculated. The ionization energy of implanted aluminum as measured by Hall effect and admittance spectroscopy ranges from 101 meV to 305 meV depending on the doping concentration.

Abstract: Various bio-related processes are driven by electron transfer reactions. Therefore the electronic structures of bio-molecules in their living environment are keys of their functionalities. One significant example photosynthesis which has attracted much attention due to urgent necessity of clean energy source. In this study, we carried out photoelectron yield spectroscopy (PYS) measurements to demonstrate the electronic structures of oligomerizedChl-a molecules, which is known as an essential reaction center of the photosystem in general green plants, under the atmospheric environment. The ionization energies of the Chl-a aggregates are successfully derived.

Abstract: The total energies of 4H-SiC with donor-acceptor-donor (D₂A) trimer codopants (D = N, P, As, and Sb, A = B, Al, Ga, and In), the formation energies of D₂A, DA, D, and A species and the binding energies were studied using ab initio calculations in order to determine the stable structures of D₂A trimer codopants in 4H-SiC. The results of the calculations indicated that some of the trimer codopants were formed and were stable in 4H-SiC. In particular, N₂Al, N₂Ga and N₂In trimer codopants with N(C_h)-Al/Ga/In (Si_k)-N(C_h) configuration and As₂B trimer codopants with As (Si_h)-B(C_k)-As (Si_h) configuration stably exist in 4H-SiC under the doping condition wherein the concentration ratio of donors to acceptors is 2 : 1.

Abstract: In the present paper, boron-doped diamond was synthesized by static pressure method using Fe-Ni-C-B system catalyst, whose resistance-temperature characteristic curve was studied. Experiments results proved that the boron-doped diamond has different ionization energy in different temperature interval and the reasons were analyzed. The maximum operating temperature is about 773K for such boron-doped diamond. The research provides experimental basis for high-temperature semiconductor diamond.

Abstract: The simulation of the incomplete ionization of substitutional dopants in Silicon Carbide (SiC) is often performed using Boltzmann statistics and ionization energy values that do not depend on free carrier concentrations. But in the case of heavy doping Fermi-Dirac statistics is needed, while the case of an inhomogeneous dopants distribution or that of an excess carrier injection requires local free carrier concentration-dependent impurity ionization energies. Here a model for describing partial ionization from diluted to high homogeneous doping densities in SiC and in thermal equilibrium is presented and compared with results on Phosphorus doped 4H-SiC.

Abstract: The analysis of the donor-acceptor pair luminescence of P-Al and N-Al pairs obtained recently for the cubic 3C polytype of SiC is viewed in some detail. A detailed consideration is given to the fitting procedure applied to the P-Al and N-Al spectra. Fit with theoretical models of spectra of type I and type II are applied to both N-Al and P-Al experimental spectra, and it is demonstrated that only contribution from P on Si site is observable in the presented samples. The accuracy of the obtained phosphorus ionization energy of 48.1 meV is also discussed.

Abstract: 6H-SiC was doped with phosphorus (P) donors by neutron transmutation. IR transmission spectra were taken in the temperature range from 6 K to 300 K. A great number of absorption lines is observed at temperatures below 140 K; these lines are attributed to transitions of the donor electron between ground states and bound excited states of P-related donors. Based on Faulkner's theory, three series of effective-mass-like states (P1, P2, P3) could be identified. The corresponding ground state energies are: E(P1) = EC - 91.5 meV, E(P2) = EC - 81.8 meV, E(P3) = EC - 73.5 meV.

Abstract: 4H-SiC implanted with high dose of phosphorus has been shown to exhibit lower sheet resistance than 4H-SiC implanted with high dose of nitrogen. In this paper, we have implanted various doses (1x1014cm-2, 2x1014cm-2, 1x1015cm-2 and 4x1015cm-2) of phosphorus into 4H-SiC in order to extract the ionization energy of phosphorus in 4H-SiC as a function of the doping concentration. Variable temperature Hall effect measurements were performed in the temperature range from 60-600K. Least square fits using the charge neutrality equation with two donor levels were used to extract the ionization energies and donor concentrations from the measured data. The ionization energies for both, the hexagonal (53meV, 49meV and 26meV) and the cubic (109meV, 101meV and 74meV) site decreased as the donor concentration (5x1018cm-3, 9.8x1018cm-3 and 3.4x1019cm-3) increased.

Abstract: Only recently the well-resolved hyperfine structure of the P6/P7 EPR center has been experimentally observed. Based on the calculated hyperfine tensors we assign the P6/P7 center to the high spin state neutral divacancy, which is the ground state in agreement with the experiment. We propose a mechanism to explain the loss of divacancy signal at high tem- perature annealing in semi-insulating SiC samples. We discuss the possible correlation between the divacancy and some photoluminescence centers.