Semi-insulating GaAs detectors optimized for fast neutron detection

Abstract

Semi-insulating (SI) GaAs detectors with a HDPE (High Density PolyEthylene) conversion layer were optimized for detection of fast neutrons (from 0.5 MeV to 12 MeV). Based on previous simulations of neutron transport in HDPE and SI GaAs carried out by the Monte Carlo radiation transport computer code MCNPX (Monte Carlo N-Particle eXtended, version 2.5.0) we used a SI GaAs wafer with a larger thickness of 270 µm. The area of a single AuZn Schottky contact was enlarged from 6.25 mm 2 to 7.36 mm 2 . Thanks to the pixel structure of the new metallization the breakdown voltage increased from 60 V to 280 V as deduced from the measured I −V characteristics. Various thicknesses of HDPE layers in the range from 100 µm to 2000 µm were used with SI GaAs detectors for neutron conversion. The measured relative detection efficiency for fast neutrons using SI GaAs detectors with various HDPE thicknesses varied from 0.07 to 0.12% at lower applied voltages, with a maximum for a 500 µm thick conversion layer.

Semi-insulating GaAs based detector of fast neutrons produced by D–T nuclear reaction

“…The HDPE layer of thickness in range from 50 to 3200 µm was fixed at the surface of the Schottky metallization by a dielectric polypropylene (PP) based glue (about 2 µl) diluted with toluene (10% solution), minimizing the prospective roughness of the detector or HDPE layer and preventing any air gap formation. Moreover, the insulating nature of the PP glue decreases the detector reverse current by a few nA [6]. Detectors were operating during irradiation under various applied reverse voltages in the range from 50 V up to 350 V. Except frontal irradiation, when the neutrons impinged the HDPE layer side of the detector perpendicularly, also the effect of various angles of incidence of neutrons on measured spectra and evaluated detection efficiency was studied.…”

“…Semiconductor based detectors with a neutron conversion layer present a very promising solution of fast neutron detectors, exhibiting compactness, small dimensions and high spatial resolution. Conversion layers for fast neutrons are attached to the detector in contact planar geometry and are usually based on polyethylene (PE) [1][2][3] or high density polyethylene (HDPE) [4][5][6], but also on fast plastic scintillator [7].…”

“…We have optimized our bulk semi-insulating (SI) GaAs detectors for fast-neutron detection by a multi-pixel structure of a Schottky contact before [6] and have tested the detectors using a 239 Pu-Be source of fast neutrons with a continuous spectrum up to 12 MeV and mean energy of about 4 MeV. The maximum obtained experimental detection efficiency was 0.113% with a 500 µm thick HDPE layer at a 100 V reverse voltage.…”

Fast neutron detector based on surface-barrier VPE GaAs structures

“…Detectors based on bulk semi-insulating (SI) GaAs are promising due to high radiation resistance, good detection characteristics and low cost [12][13][14]. The main drawback of these devices is the high sensitivity to γ-rays, therefore γ-background radiation shielding [12,14] or using of such detectors at partial depletion mode [7] are required.…”

Characterization and simulation of fast neutron detectors based on surface-barrier VPE GaAs structures with polyethylene converter

“…Neutron detectors based on bulk GaAs [13][14][15][16] have found their niche due to their high radiation resistance, good detection characteristics, low cost and also due to more advanced device technology (compared to the wide-bandgap materials).…”