Fabrication and Luminescence Characterization of Ge Wires with Uniaxial Tensile Strains Applied using Internal Stresses in Deposited Metal Thin Films

We examined the fabrication process of uniaxial tensile-strained Ge wires in micro-bridge structures by utilizing the internal stresses in deposited metal thin films. This method enables strain control by adjusting film-deposition conditions, which is advantageous over previous methods that utilize internal stresses unintentionally applied to Ge-on-insulator substrates. We evaluated the internal stresses in W films formed by sputtering deposition methods. Tensile and compressive stresses were determined based on the Ar gas pressure during the deposition process. We applied tensile strain to Ge wires using 100-nm-thick W films, each with a tensile stress of 890 MPa, deposited in 1.5-Pa Ar gas. We confirmed that strains of up to 1.62% can be achieved and controlled by tuning the structural parameters of the bridge structure with the Ge wires. Photoluminescence peaks shifted to lower energies with increasing strain, in good agreement with theoretical predictions. We also used strained Ge wires to fabricate light-emitting diodes that exhibited clear electroluminescence peaks indicative of band structural modulation in the Ge wires.