Strain distributions and electronic property modifications in Si/Ge axial nanowire heterostructures

Abstract

Molecular dynamics simulations were carried out for Si/Ge axial nanowire heterostructures using modified effective atom method ͑MEAM͒ potentials. A Si-Ge MEAM interatomic cross potential was developed based on available experimental data and was used for these studies. The atomic distortions and strain distributions near the Si/Ge interfaces are predicted for nanowires with their axes oriented along the ͓111͔ direction. The cases of 10 and 25 nm diameter Si/Ge biwires and of 25 nm diameter Si/Ge/Si axial heterostructures with the Ge disk 1 nm thick were studied. Substantial distortions in the height of the atoms adjacent to the interface were found for the biwires but not for the Ge disks. Strains as high as 3.5% were found for the Ge disk and values of 2%-2.5% were found at the Si and Ge interfacial layers in the biwires. Deformation potential theory was used to estimate the influence of the strains on the band gap, and reductions in band gap to as small as 40% of bulk values are predicted for the Ge disks. The localized regions of increased strain and resulting energy minima were also found within the Si/Ge biwire interfaces with the larger effects on the Ge side of the interface. The regions of strain maxima near and within the interfaces are anticipated to be useful for tailoring band gaps and producing quantum confinement of carriers. These results suggest that nanowire heterostructures provide greater design flexibility in band structure modification than is possible with planar layer growth.

Counterintuitive strain distribution in axial (In,Ga)N/GaN nanowires

“…The results obtained in this work for 0001 -oriented (In,Ga)N/GaN NWs are also valid for other axial semiconductor NW heterostructures, including all 0001 -oriented wurtzite NWs, but also 111 -oriented NWs composed of diamond and zincblende materials such as Ge/Si [33][34][35], Si/GaP [36], InAs/InP [37,38], CdTe/ZnTe [39]. For all these materials systems, the strain anomaly investigated in the present work is not only of academic interest, but has potentially far-reaching consequences for their application in electronic and optoelectronic devices.…”

Strain and Stability of Ultrathin Ge Layers in Si/Ge/Si Axial Heterojunction Nanowires

“…In these thin and highly strained layers, the stress is expected to lead to band structure changes and carrier confinement effects analogous to that predicted for an ideal 1 nm Ge layer embedded in a Si nanowire. 2 We find that Si/Ge biwire structures can also be grown with sharp compositional gradients and no defects. Figure 2 shows a TEM image of a Si/Ge biwire with a 6 nm thick Ge layer with GPA measurements of strain and lattice rotation.…”

(Invited) Fabrication and Properties of Abrupt Si-Ge Heterojunction Nanowire Structures

“…Theoretical calculations have shown that such a structure should show large straininduced effects on the electron energy band structure and deeper carrier confinement than the Si-Ge single junction structure [20]. The slow growth kinetics using the AlAu 2 catalyst at low temperature that were demonstrated in Fig.…”