Reflectivity and Dynamic Gratings in Implanted Si Induced by Picosecond Laser Pulses

Abstract

The relaxation processes are investigated in high-excited ion-implanted silicon using transient-reflectivity and dynamic grating methods in the picosecond time domain. The dependences of the optical parameters of ion-implanted Si versus implantation dose are presented. The temporal behaviour of the non-equilibrium charge carriers obtained from the induced-reflectivity change and grating decay measurements is analysed. Tho reflectivity decay procees is found to be always faster than the corresponding grating decay process. By the numerical calculations the surface recombination velocity is estimated to AS = 4 x lo4 cmls. The influence of the implantation process on the effectivo carrier lifetime is discussed.Frequency properties of semiconductor devices are mainly determined by the lifetime of non-equilibrium charge carriers (NCC). Applying ion-implantation technology the lifetime of NCC can be controlled in a wide range of time scale [l to 51. The exact influence of ion implantation on the behaviour of Si substrate NCC system is still unknown.I n this paper some experimental results are presented regarding the relaxation processes in high-excited ion-implanted silicon using transient reflectivity and dynamic grating methods. The used well-known excite and probe techniques are based on the generation of free carriers by a laser pulse (Aex = 0.53 pm, zi = 25 ps) and the test of the photoinduced optical properties by a time-delayed probe pulse (A, = 1.06 pm, zi = 30 ps). Dynamic gratings are induced by two identical doublefrequency picosecond pulses of a Nd:YAG laser with angle of intersection 0 = 2.6" and energy density I = 10-2 J/cma. The diameters of the pump and probe beams are d,, = 0.3 mm and d,, = 0.1 mm, respectively.In our time-resolved reflectivity measurements the strong second-harmonic pulse and the attenuated fundamental one act as excitation and probe pulses, their diameters correlate as 10: 1, respectively. The excitation pulse is perpendicularly incident on 1) Sauletekio al. 9-3, SU-292054 Vilnius, USSR.