Defect production in strained p-type Si1-xGex by Er implantation

Abstract

Strained p-Si1−xGex (x = 5.3%, 10.2%, and 15.4%) was irradiated at room temperature with 160 keV 166Er2+ ions to a fluence of 1×1010 or 3×1013 Er/cm2. The defects induced by ion implantation were investigated experimentally using high-resolution x-ray diffraction, Rutherford backscattering and channeling spectroscopy, and deep level transient spectroscopy. X-ray diffraction indicates that the damage induced by Er implantation produces a slight perpendicular expansion of the SiGe lattice. For all compositions, channeling measurements reveal that Er implantation in p-Si1−xGex to a fluence of 3×1013 Er/cm2 induces an amorphous region below the Si1−xGex surface. Annealing at 850 °C for 30 s, results in a reduction in damage density, a relaxation of the implantation-induced perpendicular expansion of the SiGe lattice in the implanted region, while a more pronounced relaxation of the compressive strain SiGe is observed for higher Ge content (x = 0.10 and 0.15). On the other hand, for the annealed SiGe samples that were implanted with Er at the fluence of 1010 Er/cm2, the compressive strain in the SiGe layer is nearly completely retained. Deep level transient spectroscopy studies indicate that two prominent defects with discrete energy levels above the valence band are introduced during Er implantation. Their activation energy was found to decrease with increasing Ge content. However, the relatively large local strain induced by high fluence Er implantation reduces the activation energy by 40 meV with respect to the low fluence Er implanted p-Si1−xGex. This shift (40 meV) in the activation energy remains constant regardless of the Ge content, suggesting that the Si1−xGex layers remained fully strained after Er implantation. The observed defects are further compared to those introduced by alpha particle irradiation and electron beam metal deposition. The results indicate that defects introduced by Er implantation have similar electronic properties as those of defects detected after electron beam deposition and alpha particle irradiation. Therefore, it is concluded that these defects are due to the Er implantation-induced damage and not to the Er species specifically.