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A mathematical model of Ni-63 source for betavoltaic batteries is presented, based on Monte Carlo calculation. Trajectories of beta particles are simulated in Ni-63 source until their escape or total energy dissipation. Analysis of the effect of physical and technological factors on the performance of a source is carried out. Special attention is given to self-absorption and substrate backscattering because of their impact on power emission. Addition of a protective layer diminishes the source emission because of further absorption. The model has been tested successfully for Ni-63/GaN structure.

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We study the electronic, optic and transport properties of both bulk materials ErN and Er0.125Ga0.875N, where crystallize in zinc-blind and wurtzite structure respectively which are materials involved form a quantum well devices.Based on density functional theory, by applying the full-potential linearized augmented plane-wave method with spin orbit coupling effect. Theanalysis of the electronic properties show that the ErN and Er0.125Ga0.875N has a band gap at 0.79 and 3.38eV respectively. on the other hand, the technology makes possible to stack these materials for a quantum well heterostructure of Er0.125Ga0.875N/ErN.The optical properties such as optical coefficients, refractive index and extinction coefficient are discussed in detail. The transport properties of alloys are investigated using the semi-classical Boltzmann theory as implemented in the BoltzTraP code in conjunction with ab initio electronic structure calculations. Our result shows that Er doping of wide band gap semiconductors is could be a potential candidate for quantum wells devices.