| AVS 62nd International Symposium & Exhibition | |
| Electronic Materials and Processing | Monday Sessions |
| Session EM+NS+PS-MoA |
| Session: | More Moore! II |
| Presenter: | Nalin Fernando, New Mexico State University |
| Authors: | N. Fernando, New Mexico State University T.N. Nunley, New Mexico State University S. Zollner, New Mexico State University D. Zhang, University of Delaware R. Hickey, University of Delaware J. Kolodzey, University of Delaware |
| Correspondent: | Click to Email |
We calculate the dependence on composition and strain of the band structure of Ge1-ySny alloys grown pseudomorphically on Ge and compare with spectroscopic ellipsometry measurements. Germanium is an indirect band gap material with limited optoelectronic applications. Because the band structure of Ge is a strong function of strain, a transition from an indirect to a direct band gap has been found for Ge under a tensile strain, which constrains the layer thickness and the composition of the substrate for heterostructure growth. Indirect to direct band gap crossover of unstrained Ge1-ySny has been reported for y~6-10% indicating the possibility of widespread applications of Ge-based photonic devices and paving the way for the design of Ge1-ySny lasers. Hence it is important to study the compositional dependence of the Ge1-ySny band structure through measurements of the optical properties of Ge1-ySny alloys. The complex pseudodielectric functions of pseudomorphic Ge1-ySny alloys grown on Ge by MBE were measured using spectroscopic ellipsometry at 300 K in the 0.76-6.6 eV energy range for Sn contents up to 11%. Dielectric functions of Ge1-ySny alloys were obtained to investigate the compositional dependence of the E1 and E1+ Δ1 critical point (CP) energies. CP energies and related parameters were obtained by analyzing the second-derivative of the dielectric function. Our experimental results are in good agreement with the theoretically predicted E1 and E1+ Δ1 CP energies of compressively strained Ge1-ySny on Ge based on deformation potential theory. We will discuss the compositional and strain dependence of the direct and indirect band gaps as well as E1 and E1+ Δ1 CP energies and related parameters of Ge1-ySny alloys. We will present the nature of the band gap of pseudomorphic Ge1-ySny on Ge and will discuss the effects of strain which critically depend on the bowing parameter of the lattice constant.