Infrared Measurement of Carrier Density, Lattice Temperature and Melt Depth during Nanoseoond Pulsed Laser Annealing of
- PDF / 414,108 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 29 Downloads / 216 Views
INFRARED MEASURMEMN OF CARRIER EENSITY, LAWTICE TI1ERATURE AND MELT DEPTH DURING NANOSEKX)ND PUISED LASER ANNEALING OF SILICOtN AND GERMANIUM J. S. Preston, H. M. van Driel and J. E. Sipe Department of Physics and Erindale College University of Toronto Toronto, Ontario, Canada, M5S IA7 ABSTRACT We have performed infrared reflectivity measurements using 5.3 and 10.6pm probes to determine the plasma density, lattice temperature and melting kinetics of silicon and germanium following excitation by 25 nanosecond, 0.53 and 1. 06pm pulses. Below the threshold of melting, the 3 maximum plasma densities are approximately 1020 am- for both materials; these values and the spatial and temporal evolution of the plasma are consistent with well known generaticn, diffusion and recombination processes. Above the threshold for melting we have taken advantage of the large skin depth at infrared wavelengths to determine the melt front kinetics for depths up to 1000 A using a contactless technique. INTRODULTION The threshold characteristics of pulsed laser induced phase transitions and annealing phenomena in semicanductors continues to be of keen interest particularly with respect to the role of high-density electron-hole plasmas produced by the laser. Although it is widely acknowledged that the induced phase transitions are purely thermal (conventional melting) in nature, knowledge of the plasma characteristics are potentially important because it is the plasma in which the laser energy is initially deposited, and the diffusion, recombination and lattice coupling of the plasma determine the spatial and temporal scales over which energy is released to the lattice. In addition, for high plasma densities, such optical properties of the material as interband and free-carrier absorption or reflectivity may be modified, thereby influencing the energy deposition processes. Over the past fifteen years [1] visible laser sources have been used to identify the onset of the molten phase through the large change in reflectivity which accompanies the semiconductor to metal transition while the lattice undergoes a solid-liquid structural transition. Several authors [2] have also used nanosecond and picosecond visible and near-visible probes to study transient states of the laser-induced solid-state plasmas, but only qualitative information [3] can be obtained because of the weak (and complex) density and band structure dependence of the dielectric function in this frequency region; interband contributions are comparable to intraband (Drude-like) contributions and temperature induced changes can dominate plasma induced changes. In the infrared, for frequencies less than the optical absorption edge, the Drude contribution dominates and is a strong function of plasma density. Gallant, Hein and van Driel [4] have recently demonstrated the use of a 10.6pm probe to determine the plasma density in Ge following 80 nsec, 1. 06pnm excitation. In addition, because the Drude dielectric function also depends on the temperature dependent carrier lattice collisic
Data Loading...
