Neutron Transmutation Doped Silicon Research Articles

Particle identification using digital pulse shape discrimination in a nTD silicon detector with a 1 GHz sampling digitizer

In beam test experiments have been carried out for particle identification using digital pulse shape analysis in a 500 μm thick Neutron Transmutation Doped (nTD) silicon detector with an indigenously developed FPGA based 12 bit resolution, 1 GHz sampling digitizer. The nTD Si detector was used in a low-field injection setup to detect light heavy-ions produced in reactions of ∼ 5 MeV/A 7Li and 12C beams on different targets. Pulse height, rise time and current maximum have been obtained from the digitized charge output of a high bandwidth charge and current sensitive pre-amplifier. Good isotopic separation have been achieved using only the digitized charge output in case of light heavy-ions. The setup can be used for charged particle spectroscopy in nuclear reactions involving light heavy-ions around the Coulomb barrier energies.

The Fission-fragment Spectrometer VERDI

VERDI (VElocity foR Direct particle Identification) is a fission-fragment spectrometer presently under construction at the Joint Research Centre IRMM. It will allow measuring the kinetic energy and the velocity of both fission fragments simultaneously. The velocity information provide information about the pre-neutron mass of each fission fragment when isotropic prompt-neutron emission from the fragments is assumed. The kinetic energy, in complement of the velocity, will provide us with the post-neutron mass. From the difference between pre- and post-neutron masses the number of neutrons emitted by each fragment may be deter- mined. Knowledge of this quantity as a function of the total kinetic energy will contribute to the understanding of how the available excitation energy is shared between both fission fragments at scission. The contemplated pre-neutron mass resolving power, A/ΔA, of at least 126 requires a time-of-flight (TOF) resolution better than 200 ps (FWHM) and an energy resolution, ΔE/E of 0.3% for a post-neutron mass. The VERDI spectrometer provides the best compromise between geometrical efficiency and time of flight. It consists of an electron detector located very close to the fissionable target and a double array of silicon detectors located 50cm away on both sides of the target. Each silicon detector has an area of 450 mm2 and is made from neutron transmutation-doped (NTD) silicon to reduce rise-time variation, to minimize pulse height defect and to reduce the plasma delay time. The intrinsic timing resolution of the electron detector was determined, using a 241Am alpha source (Eα = 5.49 MeV), against a previously characterized single-crystal diamond to σ = 140 ps. The timing resolution of the NTD silicon detectors was determined using the spontaneous fission of 252Cf in conjunction with Monte-Carlo simulations to σNTD = 150 ps. With the present timing resolution, σTOF < 210 ps, VERDI is already close to the set goals. The excellent timing properties of VERDI will also permit studying prompt and delayed gamma-ray characteristics.

Study of the recombination properties of thermostable radiation defects in p–n structures manufactured in high resistivity neutron transmutation-doped silicon

The results of the change of the charge-carrier lifetime have been analyzed, and kinetics of accumulation and annealing of defects in p+–n structures fabricated in high-resistance neutron transmutation-doped (NTD) silicon, irradiated by electrons with the energy of 6MeV and annealed at temperatures 20–600°C has been investigated. Data on the structures fabricated in phosphorus-doped Cz silicon are also given. The conclusion has been made that with the help of radiation-thermal processing it is possible to realize effective methods of improving the performance of semiconductor devices manufactured on the basis of NTD silicon as well as on the basis of Cz silicon.

Multivacancy clusters in neutron-irradiated silicon

The characteristics and annealing behavior of vacancy clusters in neutron transmutation doped silicon (NTDSi) were investigated by means of Fourier transform infrared spectroscopy (FTIR) and photoinduced transient spectroscopy. FTIR results showed that three IR absorption peaks at 707, 742, and 776 cm−1 occurred during annealing NTDSi samples at temperatures ranging from 350 to 600 °C. By comparing the present results with those reported earlier, the defect center (we named it the P0 center) which gives rise to these IR absorption bands, was assumed to be a multivacancy cluster consisting of at least six vacancies. Photoinduced transient spectroscopy results showed that a P0 center introduced two acceptor levels at Ec−0.427 eV and Ec−0.524 eV inside the energy gap.

Detection of residual defects in silicon doped by neutron transmutation

Proton implantation into neutron transmutation doped (NTD) silicon generates three hydrogen-related effective mass-like donors with binding energies between 35 and 44 meV. The donors are formed by the complexing of hydrogen with damage induced by the irradiation. Our results indicate residual defects even in well annealed NTD silicon.

Investigation of neutron radiation defects in silicon by high discriminability deep level transient spectroscopy (HDDLTS)

Neutron radiation induced defects in neutron-transmutation doped (NTD) silicon containing preexisting electron traps have been investigated by means of high discriminability deep level transient spectroscopy (HDDLTS). The experimental results show that the preexisting defects influence the formation and annealing behavior of neutron radiation-induced defects, and reduce the introduction rates of some radiation defects. Some of the radiation defects and the preexisting defects are suggested to be di- or multi-vacancy complexes.

Photo-induced current transient spectroscopy for high-resistivity neutron-transmutation-doped silicon

Defects in high-resistivity neutron-transmutation-doped (NTD) silicon prior to annealing were studied by photo-induced current transient spectroscopy (PICTS). The thermal-neutron fluence was 9.5*1017 cm-2 to give a resistivity of about 30 Omega cm after annealing, and the fast-neutron fluence was 9.5*1016 cm-2. Four traps with thermal emission activation energies of 0.15, 0.41, 0.47 and 0.50 eV were observed in NTD silicon. A trap with a thermal emission activation energy of 0.15 eV was considered to correspond to a divacancy. Although the clustered nature of the defects was observed, PICTS measurements suggest that the material state of high-resistivity NTD silicon is still crystalline and not amorphous.

Optical Current DLTS with a Bipolar Rectangular Weighting Function for High-Resistivity Neutron Transmutation Doped Silicon

AbstractDefects in high-resistivity neutron transmutation doped (NTD) silicon without annealing were characterized by optical current DLTS with a bipolar rectangular weighting function using a GaAs LED. The DLTS method with a bipolar rectangular weighting function was also described. Two clear peaks labeled A and B were observed in addition to unresolved peaks due to overlaps of DLTS signals of several defects. The thermal emission activation energies of defects A and B were 0.15 and 0.50 eV, respectively. The DLTS signals of these defects were broader than the calculated ones. This indicates the clustered nature of defects produced by fast neutron irradiation. However, the fact that the characteristic peaks were observed suggests that the material state of high-resistivity NTD silicon is crystalline but not amorphous.

Annealing effects of NTD silicon for semiconductor power devices

The use of neutron transmutation doped (NTD) Si has become very important for processing high-voltage power devices. A simple annealing process is usually required to anneal the lattice defects caused by neutron irradiation. This is usually performed by the silicon supplier by annealing the silicon crystal at a low temperature (approximately 700°C). High-voltage power devices, however, require much higher processing diffusion temperature. In situ annealing of silicon, therefore, can occur during device processing. Furthermore, we demonstrate here that higher yield can be obtained using the in situ annealing. This improvement is due to the effectiveness and uniformity of annealing of thin wafers. The uniformity and blocking voltage distribution of high-voltage rectifiers and thyristors using crystal annealed and in situ wafer annealed NTD silicon are presented.

The resistivity inhomogeneity and the maximum possible mean resistivity of neutron-transmutation doped silicon

Neutron-transmutation doping of silicon stimulates to a high degree the production of high resistivity n-type silicon, adjustable in the resistivity range of rho n=1...100 k Omega cm. Theoretical analysis of the resistivity inhomogeneities of neutron-transmutation doped silicon (NTD-Si) and the maximum possible mean resistivity as a function of the electrical parameters of the p-type Si starting material is presented. Theoretical and experimental results are compared in the resistivity range rho n=2-50 k Omega cm.

Radiation damage in neutron transmutation-doped silicon. II. Infrared study

Infrared absorption study of the annealing behavior of defects in neutron transmutation-doped silicon is reported in this paper. Infrared absorption measurements were carried out in the region 10 000–400 cm−1. This has shown the presence of extended band edge tailing, divacancy associated bands (5882, 2900, and 2760 cm−1) and higher order bands (1300–700 cm−1) at different stages of isochronal annealing from 423 to 873 K. The study of higher order bands under illumination with monochromatic light of wavelength varying from 0.5 to 1.5 μm has helped in understanding the nature of the transitions responsible for higher order bands. These bands disappear on annealing at 873 K, and no new bands appear on further annealing the sample to 1223 K. By correlating the present results with our earlier electron paramagnetic resonance results, we have postulated the formation of voids at higher temperatures of isochronal annealing.

Radiation damage in neutron transmutation-doped silicon. I. Electron paramagnetic resonance study

The removal of the radiation damage in neutron transmutation-doped silicon during the isochronal annealing from a temperature of 423–1223 K has been monitored by electron paramagnetic resonance spectroscopy. The dominant defect centers have been identified to be P1, A2, A4, A8, and A11. Complete decay of all the defect centers has been found to take place on annealing at 923 K, where a complete recovery of conduction electron spin resonance signal also takes place.

Neutron transmutation doping of silicon. II. Resistivity inhomogeneity as a function of compensation ratio

The resistivity inhomogeneity in neutron transmutation doped (NTD) silicon is a function of both the initial inhomogeneity before transmutation doping and the final compensation ratio after transmutation doping which, in turn, is a function of the irradiation thermal-neutron fluence. Calculations of this inhomogeneity Δρ/? as a function of compensation ratio are presented. These calculations are then compared to experimental data obtained by probe measurements of NTD silicon compensated to resistivities as high as 100 000 Ω cm. Calculations are also presented which yield the maximum possible mean resistivity which can be obtained, given an initial Δρ/?, before fluctuation-induced mixed typing occurs.