Defects engineering has shown that intrinsic defects in semiconductor devices have not only negative function, but also positive. Experiments have shown a possibility to form p-n junction at a surface ofi-type semiconductor by laser radiation. Summarising the experimental results, the model of laser radiation interaction with i- type semiconductor is developed. The main role in p-n junction formation is to high gradient of temperature, as a result interstitial atoms and vacancies drift opposite directions: vacancies into semiconductor bulk, but interstitial atoms to the surface. Vacancies have positive charge, but interstitial atoms have negative one, thereby, p-n junction is formed. The model was proved by Volt-Ampere characteristics measurement method.