Linyue Liu

Proton Irradiation Effects on AlGaN/AlN/GaN Heterojunctions

AlGaN/AlN/GaN heterojunctions were irradiated by 3 MeV protons with different fluences. Hall and C-V measurements showed that the density and mobility of 2DEG for heterojunctions decreased after proton irradiation. The crystal quality and optical properties of AlGaN/GaN heterojunctions were characterized by the variations of the micro-Raman scattering spectra, XRD and photo luminescence (PL) spectra with proton fluence. It has been obtained that the strain and dislocation of GaN and AlGaN were not affected by the proton injected. The proton irradiation caused the increase of structural defects in HT-AlN buffer layer, which lead to the red shift of A1 (LO) mode. The higher tails of XRD rocking curve indicated the introduction of point defects by irradiation. The full-width at half-maximum (FWHM) of E2high phonon mode broadened, which was consistent with change of FWHM of PL near-band-edge emission (BE). The spectra of yellow band normalized to the intensity of BE demonstrated a great increase of Ga vacancies related defects, which may be the main reason for the degradation of optical properties.

Polycrystalline diamond based detector for Z-pinch plasma diagnosis

A detector setup based on polycrystalline chemical-vapor-deposition diamond film is developed with great characteristics: low dark current (lower than 60 pA within 3 V/mum), fast pulsed response time (rise time: 2-3 ns), flat spectral response (3-5 keV), easy acquisition, low cost, and relative large sensitive area. The characterizing data on Qiangguang-I accelerator show that this detector can satisfy the practical requirements in Z-pinch plasma diagnosis very well, which offers a promising prototype for the x-ray detection in Z-pinch diagnosis.

Polycrystalline CVD diamond detector: Fast response and high sensitivity with large area

Polycrystalline diamond was successfully used to fabricate a large area (diameter up to 46 mm) radiation detector. It was proven that the developed detector shows a fast pulsed response time and a high sensitivity, therefore its rise time is lower than 5 ns, which is two times faster than that of a Si-PIN detector of the same size. And because of the large sensitive area, this detector shows good dominance in fast pulsed and low density radiation detection.

Radiation Resistance of Silicon Carbide Schottky Diode Detectors in D-T Fusion Neutron Detection

Silicon carbide (SiC) is a wide band-gap semiconductor material with many excellent properties, showing great potential in fusion neutron detection. The radiation resistance of 4H-SiC Schottky diode detectors was studied experimentally by carefully analyzing the detectors’ properties before and after deuterium-tritium fusion neutron irradiation with the total fluence of 1.31 × 1014 n/cm2 and 7.29 × 1014 n/cm2 at room temperature. Significant degradation has been observed after neutron irradiation: reverse current increased greatly, over three to thirty fold; Schottky junction was broken down; significant lattice damage was observed at low temperature photoluminescence measurements; the peaks of alpha particle response spectra shifted to lower channels and became wider; the charge collection efficiency (CCE) decreased by about 7.0% and 22.5% at 300 V with neutron irradiation fluence of 1.31 × 1014 n/cm2 and 7.29 × 1014 n/cm2, respectively. Although the degradation exists, the SiC detectors successfully survive intense neutron radiation and show better radiation resistance than silicon detectors.

The Fabrication and Characterization of Ni/4H-SiC Schottky Diode Radiation Detectors with a Sensitive Area of up to 4 cm2

Silicon carbide (SiC) detectors of an Ni/4H-SiC Schottky diode structure and with sensitive areas of 1–4 cm2 were fabricated using high-quality lightly doped epitaxial 4H-SiC material, and were tested in the detection of alpha particles and pulsed X-rays/UV-light. A linear energy response to alpha particles ranging from 5.157 to 5.805 MeV was obtained. The detectors were proved to have a low dark current, a good energy resolution, and a high neutron/gamma discrimination for pulsed radiation, showing the advantages in charged particle detection and neutron detection in high-temperature and high-radiation environments.

Development of a compact magnetic proton recoil spectrometer for measurement of deuterium-tritium neutrons.

A new compact magnetic proton recoil (MPR) neutron spectrometer has been designed for precise measurement of deuterium-tritium (DT) neutrons. This design is presented emphasizing the magnetic analyzing system, which is based on a compact quadrupole-dipole (QD) electromagnet. The focal plane detector (FPD) is also discussed with respect to application for the next step. The characteristics of the MPR spectrometer were calculated by using Monte Carlo simulation. A preliminary experiment was performed to test the magnetic analyzing system and the proton images of the FPD. Since the QD electromagnet design allows for a larger foil thickness and solid angle to be utilized, the MPR spectrometer defined in this paper can achieve neutron detection efficiency more than 5 × 10(-7) at an energy resolution of 1.5% for measuring DT neutrons.

A fast-neutron detection detector based on fission material and large sensitive 4H silicon carbide Schottky diode detector

Silicon carbide radiation detectors are attractive in the measurement of the total numbers of pulsed fast neutrons emitted from nuclear fusion and fission devices because of high neutron-gamma discrimination and good radiation resistance. A fast-neutron detection system was developed based on a large-area 4H-SiC Schottky diode detector and a 235U fission target. Excellent pulse-height spectra of fission fragments induced by mono-energy deuterium-tritium (D-T) fusion neutrons and continuous energy fission neutrons were obtained. The detector is proven to be a good candidate for pulsed fast neutron detection in a complex radiation field.

Modified timing characteristic of a scintillation detection system with photonic crystal structures

It is intuitively expected that an enhanced light extraction of a scintillator can be easily achieved by photonic crystal structures. Here, we demonstrate a modified timing characteristic for a detection system induced by enhanced light extraction with photonic crystal structures. Such improvement is due to the enhanced light extraction which can be clearly proven by the independent measurements of the light output and the timing resolution. The present investigation is advantageous to promote the development of a scintillation detection system performance based on the time-of-flight measurement.

Theoretical analysis of proton irradiation effects on AlGaN/GaN high-electron-mobility transistors

To study radiation damage, the authors irradiated AlGaN/GaN high-electron-mobility transistors with 3 MeV protons at various fluences. This irradiation caused displacement damage, which decreased the saturated drain current, maximum transconductance, cutoff frequency, and maximum frequency of oscillation. The authors extracted the damage factors of the threshold voltage, two-dimensional electron gas (2DEG) surface density, and mobility, which are usually used to simulate and estimate device performance in radiation environments. Calculations based on the charge control model show that the acceptor defects induced in the GaN layer play a leading role, while defects induced in the AlGaN barrier layer rarely matter. The removal rate of carriers from the 2DEG is unrelated to the thickness of undoped AlGaN layer, the conduction band discontinuity, and the doping concentration of AlGaN barrier layer; it only depends on the concentration of acceptor defects induced.

A theoretical and experimental research on detection efficiency of HPGe detector for disc source with heterogeneous distribution

If we treat some heterogeneous distributed media including heterogeneous distributed radioactive sources, radioactive polluted field, “hot point/hot area” and “hot particle” as uniform distributed media, directly affects the accuracy of the detection efficiency calibrated, introduced the great metrical deviation. A Standard Normal distribution disc source was simulated by a point source experiment. The detection efficiency of heterogeneous distributed disc source is defined as multiply efficiency function of point source by the probability density function. And then we carried out process of the mathematical integrality and normalization. A description of the analysis and experimental results of this method are presented. The theoretical and experimental calculation of detection efficiency of HPGe detector for heterogeneous distribution disc source is consistent with each other.