Sn-based Group-IV Semiconductors on Si: New Infrared Materials and New Templates for Mismatched Epitaxy
- PDF / 685,480 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 110 Downloads / 169 Views
0891-EE12-08.1
Sn-based Group-IV Semiconductors on Si: New Infrared Materials and New Templates for Mismatched Epitaxy
John Tolle, Radek Roucka, Vijay D’Costa, Jose Menendez, Andrew Chizmeshya and John Kouvetakis Arizona State University, Tempe AZ 85287 U.S.A. ABSTRACT We report growth and properties of GeSn and SiGeSn alloys on Si (100). These materials are prepared using a novel CVD approach based on reactions of Si-Ge hydrides and SnD4. High quality GeSn films with Sn contents up to 20%, and strain free microstructures have been obtained. The lattice mismatch between the films and Si is relieved by Lomer edge dislocations located at the interface. This material is of interest due to the predicted cross-over to a direct gap semiconductor for moderate Sn concentrations. We find that the direct band gap, and, consequently, the main absorption edge, shifts monotonically to lower energies as the Sn concentration is increased. The compositional dependence of the direct band gap shows a strong bowing, such that the direct band gap is reduced to 0.4 eV (from 0.8 eV for pure Ge) for a concentration of 14% Sn. The ternary SiGeSn alloy has been grown for the first time on GeSn buffer layers. This material opens up entirely new opportunities for strain and band gap engineering using group-IV materials via decoupling of strain and composition. Our SiGeSn layers have lattice constants above and below that of pure Ge, and depending on the thickness and composition of the underlying buffer layer they can be grown relaxed, with compressive, or with tensile strain. In addition to acting as a buffer layer for the growth of SiGeSn, we have found that GeSn can act as a template for the subsequent growth of a variety of materials, including III-V semiconductors.
INTRODUCTION It has been known for many years-on theoretical grounds-that the Si-Ge-Sn system possesses new potential for direct gap IR applications. This has stimulated intense experimental efforts to prepare such compounds, but to date materials approaching device quality have not been reported. We have recently demonstrated the fabrication of Ge1-xSnx and Ge1-x-ySixSny singlephase alloys with variable and controllable concentrations and device quality morphological and microstructural properties using, for the first time, new CVD heteroepitaxy methods. This is an important development for several reasons. First, Ge1-xSnx alloys have been predicted to undergo an indirect- to direct-gap transition so that this system may lead to the first direct-gap semiconductor fully integrated with Si technology [1]. Second, device-quality Ge1-xSnx layers of arbitrary thickness can be deposited directly on Si and these can be used as "virtual substrates" for the growth of Ge1-x-ySixSny analogs. These layers represent a new class of lattice-matched templates for the monolithic integration of technologically important II-VI and III-V compounds with Si [2]. Finally, the synthesis of Ge1-x-ySixSny makes it possible, for the first time, to decouple strain and band gap, leading to the design
Data Loading...
