UC Irvine

The narrow gap semiconductor alloys SnxGe1 - x and SnxSi1 - x offer the possibility for engineering tunable direct energy gap Group IV semiconductor materials. For pseudomorphic SnxGe1 - x alloys grown on Ge (001) by molecular beam epitaxy, an indirect-to-direct bandgap transition with increasing Sn composition is observed, and the effects of misfit on the bandgap analyzed in terms of a deformation potential model. Key results are that pseudomorphic strain has only a very slight effect on the energy gap of SnxGe1 - x alloys grown on Ge (001) but for SnxGe1 - x alloys grown on Ge (111) no indirect-to-direct gap transition is expected. In the SnxSi1 - x system, ultrathin pseudomorphic epitaxially-stabilized α-SnxSi1 - x alloys are grown on Si (001) substrates by conventional molecular beam epitaxy. Coherently strained α-Sn quantum dots are formed within a defect-free Si (001) crystal by phase separation of the thin SnxSi1 - x layers embedded in Si (001). Phase separation of the thin alloy film, and subsequent evolution occurs via growth and coarsening of regularly-shaped α-Sn quantum dots that appear as 4-6 nm diameter tetrakaidecahedra with facets oriented along elastically soft 〈100〉 directions. Attenuated total reflectance infrared absorption measurements indicate an absorption feature due to the α-Sn quantum dot array with onset at ∼0.3 eV and absorption strength of 8 × 103 cm-1, which are consistent with direct interband transitions. © 2001 Elsevier Science B.V. All rights reserved.