The Mechanism of Semiconductor Surface Nanoscale Fracture by Laser Radiation: Relaxation of Mechanical Compressive Stress

The nanoscale fracture of a semiconductor surface under the action of nanosecond Nd:YAG laser radiation has been performed. The investigation of the surface topography, optical and mechanical properties has shown that the mechanism of the surface nanoscale fracture is relaxation of mechanical compressive stress. The experiments were carried out on semiconductor crystals such as: elementary semiconductors Si and Ge; compound semiconductors GaAs and CdTe; solid solutions SiGe and CdZnTe. The nanoscale fractured surface of semiconductor possesses unique physical properties when at least one dimension of the nanoscale fracture is comparable or less than Bohr’ radius of electron, hole or exciton. The “blue shift” of the photoluminescence band maximum of the nanoscale fractured surface of Si crystal by 1.05 eV was observed. Moreover, the band intensity increased by 106 times. The dependence of laser radiation intensity on Si crystal microhardness is characterized by non-monotonous function, which has two maximums for p-type and one maximum for n-type. Our study has shown that the nanoscale fracture mechanism consists of two stages. The first stage is formation of a mechanically strained top layer on the irradiated surface of semiconductor due to redistribution of impurity atoms and intrinsic defects (interstitials and vacancies) in temperature gradient field, the so called Thermo gradient effect [1]. At the first stage of the process microhardness of p-type Si crystal increases by 40% and conversion to n-type conductivity takes place. Therefore, p-n homojunction is formed in elementary and compound semiconductors irradiated by the laser. This fact is explained by the opposite charge of interstitials and vacancies [2]. Whereas, the irradiation of solid solutions by the laser leads to formation of different phases, for example, Ge/Si. In this case, formation of p-n heterojunction takes place. The second stage is plastic deformation of the top layer due to relaxation of mechanical compressive stress. The stress in the top layer arises due to the difference in the lattice constants of the heterostructure layers and selective laser heating