Molecular-beam epitaxial growth of tensile-strained and n-doped Ge/Si(001) films using a GaP decomposition source

• Published in: Thin solid films 2014-04, Vol.557, p.70-75
• Main Authors: Luong, T.K.P., Ghrib, A., Dau, M.T., Zrir, M.A., Stoffel, M., Le Thanh, V., Daineche, R., Le, T.G., Heresanu, V., Abbes, O., Petit, M., El Kurdi, M., Boucaud, P., Rinnert, H., Murota, J.
• Format: Article
• Language: English
• Subjects: Annealing; Condensed Matter; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Decomposition; Doping; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Exact sciences and technology; Germanium; Materials Science; MBE growth; Methods of deposition of films and coatings; film growth and epitaxy; Molecular beam epitaxy; Molecular, atomic, ion, and chemical beam epitaxy; n-Doping; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optoelectronics; Photoluminescence; Physics; Silicon substrates; Substrates; Surface and interface electron states; Tensile strain Ge; Theory and models of film growth; Time measurement
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/j.tsf.2013.11.027

We have combined numerous characterization techniques to investigate the growth of tensile-strained and n-doped Ge films on Si(001) substrates by means of solid-source molecular-beam epitaxy. The Ge growth was carried out using a two-step growth method: a low-temperature growth to produce strain relaxed and smooth buffer layers, followed by a high-temperature growth to get high crystalline quality Ge layers. It is shown that the Ge/Si Stranski–Krastanov growth mode can be completely suppressed when the growth is performed at substrate temperatures ranging between 260°C and 300°C. X-ray diffraction measurements indicate that the Ge films grown at temperatures of 700–770°C are tensile-strained with typical values lying in the range of 0.22–0.24%. Cyclic annealing allows further increase in the tensile strain up to 0.30%, which represents the highest value ever reported in the Ge/Si system. n-Doping of Ge was carried out using a GaP decomposition source. It is shown that heavy n-doping levels are obtained at low substrate temperatures (210–250°C). For a GaP source temperature of 725°C and a substrate temperature of 210°C, a phosphorus concentration of about 1019cm−3 can be obtained. Photoluminescence measurements reveal an intensity enhancement of about 16 times of the direct band gap emission and display a redshift of 25meV that can be attributed to band gap narrowing due to a high n-doping level. Finally, we discuss about growth strategies allowing optimizing the Ge growth/doping process for optoelectronic applications. •We investigate the effect of tensile strain and n-doping on Ge optical properties.•We show that cyclic annealing allows getting a tensile strain up to 0.30% in Ge.•n-Doping of Ge/Si films is performed using a GaP decomposition source.•We show that n-doping is more important to enhance the photoluminescence intensity.•We present new growth strategies to develop Ge-based optoelectronic devices.