The development of growth of nanowires and branched nanowires (nanotrees(1)) in recent years has made such devices as resonant tunneling diodes(2) (RTD), single electron transistors (3) (SET) and high-frequency wrap-gated nanowire transistors possible. These heterostructures are formed by epitaxial growth in a step-wise procedure where each level can be individually controlled in terms of diameter, length and composition.
The advantage of using nanowires is that energy consumption of the devices will be low, they will be extremely small and, above all; more freely chosen combinations of materials with different lattice constants can be performed. This is due to the possibility for lateral strain relief already a few atomic layers away from the interfaces in the nanowire. However, the magnitude of the mismatch is not the only governing factor for a successful eptaxial growth; the sequence is also of great importance. For instance, growth of GaP on InP is quite feasible, but the opposite; InP on GaP, gives directional changes, crawling branches and crystal defects of the added part of the nanowire.
Here we will show results from detailed calculations of the strain distribution at interfaces of heterostructures derived from HREM atomic resolution images. We will also show which combinations of Si, Ge, In, Ga, P and As that are possible in real structures.
1). Kimberly A. Dick, Knut Deppert, Magnus W. Larsson, Thomas Mårtensson, Werner Seifert, L. Reine Wallenberg, Lars Samuelson. Nature Materials 3 (6): 380-384 (2004)
2). M. T. Björk, B. J. Ohlsson, C. Thelander, A. I. Persson, K. Deppert, L. R. Wallenberg, and L. Samuelson. Appl. Phys. Lett. 81 (2002) 4458
3). C. Thelander,T. Mårtensson, M. T. Björk, B. J. Ohlsson, M. W. Larsson, L. R. Wallenberg, and L. Samuelson. Appl. Phys. Lett. 83 (2003) 205237
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