Photovoltaic Effect Produced in Silicon Solar Cells by X- and Gamma Rays

The open-circuit voltage and photocurrent produced in a silicon solar cell by X- and gamma rays were measured as a function of exposure dose rate, cell temperature, angle of incidence of radiation, and photon energy. This photoresponse was stable and proportional to the exposure dose rate, which was applied up to a maximum of 1.8×10⁶ roentgen per minute for X-rays and 4×10² roentgen per minute for Co⁶⁰ gamma rays. At an exposure dose rate of 1 roentgen per minute the response was of the order of 10^-5 volt for the open-circuit voltage and 10^-8 ampere for the photocurrent. At high exposure dose rates of Co⁶⁰ gamma rays, radiation damage became apparent. The temperature dependence of the photoresponse was controlled by the temperature dependence of the cell resistance. The directional dependence of the photoresponse varied with the quality of radiation and for Co⁶⁰ gamma rays was very small for angles from 0° to 70°. The photoresponse decreased with increasing photon energy but changed only little between 200 and 1,250 kilo electron volts. The ratio of the response to X-rays of 38 kilo electron volts effective energy and that to Co⁶⁰ gamma rays was approximately 6:1. An approximate value of the thickness of the effective p-n junction layer is deduced from the energy dependence.