In this work, a planar electron emission device based on a graphene/hexagonal boron nitride (h-BN)/n-Si heterostructure is fabricated to realize highly monochromatic electron emission from a flat surface. The h-BN layer is used as an insulating layer to suppress electron inelastic scattering within the planar electron emission device. The energy spread of the emission device using the h-BN insulating layer is 0.28 eV based on the full-width at half-maximum (FWHM), which is comparable to a conventional tungsten field emitter. The characteristic spectral shape of the electron energy distributions reflected the electron distribution in the conduction band of the n-Si substrate. The results indicate that the inelastic scattering of electrons at the insulating layer is drastically suppressed by the h-BN layer. Furthermore, the maximum emission current density reached 2.4 A/cm2, which is comparable to that of a conventional thermal cathode. Thus, the graphene/h-BN heterostructure is a promising material for planar electron emission devices to obtain a highly monochromatic electron beam and a high electron emission current density.

The effect of gamma irradiation on two types (superstrate‐ and substrate‐type) of CdS/CdTe photodiodes, which we have proposed as potential photoconducting films for compact image sensors with a field emitter array (FEA), was investigated. A 60Co gamma‐ray source was employed, and the total gamma irradiation dose was more than 500 kGy. For the superstrate‐type structure, the irradiation caused the short‐circuit current density (JSC) to decrease, probably due to the resulting decreased transmittance of the glass substrate. On the other hand, little degradation of the I ‐V characteristics or spectral response was observed after the gamma irradiation for the substrate‐type structure. These results suggest that, taking into account the decrease in transmittance of the glass substrate, the CdS/CdTe photodiodes have sufficient tolerance to high gamma‐ray exposure. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Compact and radiation-tolerant radiation dosimeter without bias voltage application using solar cells such as CdTe was proposed for severe radiation environment near a nuclear reactor pressure vessel. In this work, γ-ray tolerance and γ-ray detection characteristics of CdTe solar cells were investigated. It was found that the CdTe solar cell has sufficient tolerance against γ-ray exposure up to 3 MGy. It was demonstrated that γ-ray induced current density linearly increased with increasing γ-ray intensity in the range up to approximately 1.5 kGy h−1. This result indicates that high dose-rate radiation detection can be performed using solar cells without voltage application. In addition, γ-ray sensitivity was successfully improved by a stack of CdTe solar cells with parallel connections. Furthermore, γ rays can be detected with high responsivity and small noise even under a high flux neutron environment.