P-n junction is the most important component of many semiconductor devices. Thermodiffusion, ion implantation and molecular beam epitaxy are only a few methods to form a p-n junction. The main drawback for these methods is high cost of equipment. Therefore this equipment is not available for small and medium companies. A possibility of p-n junction formation by laser radiation was shown in several semiconductors: p-Si, p-CdTe, p-InSb, p-InAs, p-PbSe and p- Ge. Different mechanisms have been proposed to explain the nature of inversion of conductivity type: impurities’ segregation, defects’ generation, amorphization and oxygen related donor generation. However, the proposed mechanisms have many flaws and even contradictions; therefore the mechanism of p-n junction formation by laser radiation (LR) is not clear until now. The aim of the work is to show a new possibility of p-n junction formation in intrinsic elementary semiconductor by LR without any impurities and to propose the new mechanism of p-n junction formation. II. RESULTS AND DISCUSSION We assume that, the intrinsic defects play the main role in formation of p-n junction. For this reason i-Ge crystal was irradiated by Nd:YAG laser with different energy of quantum. In experiments i-Ge single crystals with NA = 7.4 × 1011 cm-3 and ND = 6.8 × 1011 cm-3 s were used. Samples were prepared by mechanical polishing with diamond grease followed by chemical treatment with CP-4 etching solution. To form a p-n junction, nanosecond Nd:YAG laser with wavelengths λ1 = 1064 nm, λ2= 532 nm and λ3= 266 was used. Measurements of I-V characteristics were done by soldering 99% Sn and 1% Sb alloy electrical contacts directly on the irradiated surface of i- Ge and the opposite side. I-V characteristics of i-Ge samples before and after irradiation different intensities of Nd:YAG laser with wavelength 266 nm and different laser intensities are shown in Fig.1. Increase of rectification ratio (RR) of I-V characteristics with intensity of the laser radiation, energy of laser radiation quanta and numbers of pulses were observed in this experiment (see Fig.2). Moreover, this process takes place in threshold manner, it means, RR is non-monotonic function on laser radiation intensity. These results are explained by damage of p-n junction at threshold intensity (Ith) due to formation of nanocones.The mechanism of this phenomenon is explained by generation and redistribution of intrinsic point defects in temperature gradient field, which causes strongly absorbed LR. The redistribution of defects takes place because interstitial atoms drift towards the irradiated surface, but vacancies drift in the opposite direction – in the bulk of semiconductor according to Thermogradient effect [1]. Since interstitials in Ge crystal are of n-type and vacancies are known to be of p-type [2], a p-n junction is formed. III. CONCLUSIONS For the first time we have proved that the mechanism of pn junction formation in semiconductor is caused by generation and redistribution of intrinsic point defects in temperature gradient field induced by LR. Increase of rectification ratio of p-n junction with the increase of LR intensity is typical for Thermogradient effect; therefore this effect has the main role in p-n junction formation. IV. REFERENCES [1] A. Medvid: Redistribution of Point Defects in the Crystalline Lattice of a Semiconductor in an Inhomogeneous Temperature Field, Defect and Diffusion Forum , 2002, 210-212: 89-102. [2] Cor Claeys: Germanium-based technologies: from materials to devices. London Elsevier B.V. 2007 Acknowledgment: The author gratefully acknowledges financial support in part by the European Regional Development Fund within the project “Sol-gel and laser technologies for the development of nanostructures and barrier structures» No 2010/0221/2DP/2.1.1.1.0/10/APIA/VIAA/145