Neutron Radiation Effects on the Performance of the CdSe Thin Film for Photodetector Applications
Authors: Hammo Zainab , Najam Laith , Al- Taan Laith 
Published: October 2024

Cadmium Selenide CdSe thin films were deposited on (7.5×1.3×0.1 cm3) glass substrates and (1×1 cm2) p-type silicon substrates using pulsed laser deposition technique (Nd: YAG laser beam with 80 mJ energy, λ = 1064 nm). Then, they were annealed at 300 °C for 1 h to get diodes as visible light detectors. Some of these samples (diodes) were exposed to different intervals (5, 7, 9, 12) days of neutron radiation using (241Am -10Be) source with a flux of 3×105 n/cm2.s and energy of 5.71 MeV. For comparison purposes, the other diodes were kept without any irradiation The morphological and electrical properties of these samples were studied by XRD, FE-SEM and I-V measurements. Results have shown all these thin films exhibit a hexagonal structure. However, there is a slight shift in the preferred orientation (100) for the irradiated films. Also, there was a new (102 - SiO2) peak that appeared in the irradiated thin film pattern. The crystallite size of pristine and (5, 7, 9, 12) days irradiated CdSe thin films were (26.9, 18.3, 24.9, 20.3 and 24.5) nm respectively, whereas, the mean particle size of the pristine film was 37 nm whereas for the irradiated films 53, 64, 73 and 92 nm. Results also show that the band gap of these samples increased from 2.17 eV for pristine thin films to 2.3, 2.48, 2.25, and 2.3 eV for the irradiated thin films. On the other hand, the results of I-V characteristics show the dark/light current. The current under illumination increases when exposed to small values of neutron radiation then it decreases with higher values of exposure. In contrast, the dark current decreases significantly with the irradiation. The effect of the irradiation was clear on the response/recovery period for all devices. Nevertheless, it was more profound in the response/recovery time of pristine devices. Also, the photo-responsivity of the pristine device was larger than the other devices and it was decreased with increasing absorbed doses.
HIGHLIGHTS

Hexagonal Structure: All CdSe thin films (both pristine and irradiated) exhibit a hexagonal structure, with a slight shift in orientation due to neutron irradiation.
Neutron Radiation Impact: Neutron radiation causes a significant shift in crystallite size, decreasing the size for irradiated films. Additionally, a new (102 SiO2) peak emerges in irradiated samples, indicating radiation-induced changes.
Band Gap Increase: The optical band gap of the CdSe films increased with neutron irradiation, starting from 2.17 eV in pristine films to values as high as 2.48 eV after irradiation.
Morphological Changes: Irradiated films showed increased grain sizes, with neutron exposure leading to the enlargement of mean particle sizes from 37 nm in pristine samples to 92 nm in the most heavily irradiated samples.
Electrical Behavior: Neutron irradiation impacted the photodetectors' electrical properties. The light current initially increased with small neutron doses but decreased with higher doses, while dark current consistently decreased after irradiation.

GRAPHICAL ABSTRACT