tailieunhanh - Germanium band gap engineering induced by tensile strain for si-based optoelectronic applications

We show that the value of the tensile strain in the Ge layers lineally increases with increasing the growth temperature and reaches a saturation value of ∼ in the temperature range of 700-770˚C. Post-grown cyclic thermal annealing has allowed to increase the tensile strain up to , which is the highest value ever reported to date. Finally, photoluminescence measurements reveal both an enhancement of the Ge direct band gap emission and a reduction of its energy due to the presence of tensile strain in the layers. | Communications in Physics, Vol. 23, No. 4 (2013), pp. 367-375 GERMANIUM BAND GAP ENGINEERING INDUCED BY TENSILE STRAIN FOR SI-BASED OPTOELECTRONIC APPLICATIONS LUONG THI KIM PHUONG Aix Marseille University, CNRS, CINaM-UMR 7325, F-13288 Marseille, France and Hong Duc University, 565 Quang Trung St., Thanh Hoa City, Vietnam NGUYEN MANH AN Hong Duc University, 565 Quang Trung St., Thanh Hoa City, Vietnam Received 19 August 2013 Accepted for publication 24 December 2013 Abstract. We have combined structural and optical characterizations to investigate the tensilestrained state and the band gap engineering of Ge layers grown on Si(001) using molecular beam epitaxy. The tensile strain is generated in the Ge layers due to a difference of thermal expansion coefficients between Ge and Si. The Ge growth on Si(001) was proceeded using a two-step growth process: a low-temperature step to produce relaxed buffer layers, followed by a high-temperature step to generate the tensile strain in the Ge layers. For the low-temperature step, we have evidenced the existence of a substrate temperature window from 260 to 300˚C in which the well-known StranskiKrastanov Ge/Si growth mode transition from two-dimensional to three-dimensional growth can be completely suppressed. We show that the value of the tensile strain in the Ge layers lineally increases with increasing the growth temperature and reaches a saturation value of ∼ in the temperature range of 700-770˚C. Post-grown cyclic thermal annealing has allowed to increase the tensile strain up to , which is the highest value ever reported to date. Finally, photoluminescence measurements reveal both an enhancement of the Ge direct band gap emission and a reduction of its energy due to the presence of tensile strain in the layers. I. INTRODUCTION Silicon (Si), germanium (Ge) and their alloys are the main materials that are used as active layers in microelectronics. However, due to their indirect band gap the realization of .