^aLaboratory of Semiconductor Devices Physics, University Tahri Mohammed of

Bechar,Algeria

^bLaboratoty of environmental and energetics systems (L.S.E.E) at university

center Ali Kafi Tindouf Algeria

In this study, we use a Monte Carlo calculation code to simulate the concentration of electron-hole pairs generated of each point in the solid targets under a bombardment of Ni- 63 source for betavoltaic cells; this model is reported to be an accurate representation of electron interaction.From this simulation we can obtain the distribution of electron-hole pairs generated in GaN/GaN junction as a function of the depth, this distribution allowed us to find the concentrations of minority carriers excess depending on the thickness, which can represent as function and inject into the continuity equations for determine the diffusion current and then the characteristics of betavoltaic chosen. The model has been tested for Ni-63/GaN/GaN structure, with energy 17 KeV.