Physical properties of ion-implanted laser annealed n-type germanium

Abstract

An investigation is made of the impurity distribution and carrier concentration in n-type germanium layers doped with P, As, and Sb by ion implantation and recrystallized by laser annealing. The impurity distribution is determined with SIMS. The electron concentration is obtained from Hall effect and from ir reflectivity measurements. Impurity concentrations as high as 2 × 10²¹ cm⁻³ are reached, with carrier concentrations N_e as high as 2.4 × 10²⁰ cm⁻³, much higher than in bulk doped samples (N_e ≦ 4 × 10¹⁹ cm⁻³). For the P-doped samples the implanted layers are found to have a lattice constant larger than the substrate for small implantation doses and smaller for larger doses. An analysis of these data leads to the conclusion that most of the ions are implanted substitutionally and, at high concentrations, they are compensated by pairing defects, probably vacancies. With this hypothesis it is also possible to interpret the dependence of the strength of the phosphorus local mode on implantation dose, as found with Raman spectroscopy. The softening of the Raman phonon with dose observed experimentally is also compatible with this hypothesis. A softening of the acoustic phonons with dose found with Brillouin spectroscopy is also reported and discussed.