with them, however. Hence, they have limited device or integrated optics applications. Self-assembled InAs QDs can be grown on GaAs substrates through the Stranski-Krastanov growth mode.51,52 This type of QD has about 5 to 10 percent non-uniformity. However, recent advances have been made in diode lasers and semiconductor optical amplifiers53,54 to exploit QDs. These are very promising for deployment in the near future.
The top-down approach involves various lithography techniques to define the structures, using e-beam lithography, nanoimprint,55,56 or dip pen technologies57 and subsequent etching or growth of materials. These methods can lead to higher uniformity, but they still suffer from surface defects.58,59
Synthetic biology is a new field of biological research and technology development that combines science and engineering with the goal of designing and constructing novel and useful biological systems not found in nature. Synthetic biology has provided the means of both genetically engineering specific optical properties
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52 Eaglesham, D.J., and M. Cerullo. 1990. Dislocation-free Stranski-Krastanow growth of Ge on Si(100). Physical Review Letters 64:1943-1946.
53 Zhukov, A.E., A.R. Kovsh, V.M. Ustinov, Y.M. Shernyakov, S.S. Mikhrin, N.A. Maleev, E.Y. Kondrat’eva, D.A. Livshits, M.V. Maximov, B.V. Volovik, D.A. Bedarev, Y.G. Musikhin, N.N. Ledentsov, P.S. Kop’ev, Z.I. Alferov, and D. Bimberg. 1999. Continuous-wave operation of long-wavelength quantum-dot diode laser on a GaAs substrate. IEEE Photonics Technology Letters 11:1345-1347.
54 Akiyama, T., M. Ekawa, M. Sugawara, K. Kawaguchi, Hisao Sudo, A. Kuramata, H. Ebe, and Y. Arakawa. 2005. An ultrawide-band semiconductor optical amplifier having an extremely high penalty-free output power of 23 dBm achieved with quantum dots. IEEE Photonics Technology Letters 17:1614-1616.
55 Vieu, C., F. Carcenac, A. Pepin, Y. Chen, M. Mejias, A. Lebib, L. Manin-Ferlazzo, L. Couraud, and H. Launois. 2000. Electron beam lithography: Resolution limits and applications. Applied Surface Science 164:111-117.
56 Colburn, M., S.C. Johnson, M.D. Stewart, S. Damle, T.C. Bailey, B. Choi, M. Wedlake, T.B. Michaelson, S.V. Sreenivasan, J.G. Ekerdt, and C.G. Willson. 1999. Step and flash imprint lithography: A new approach to high-resolution patterning. Proceedings of the SPIE 3676:379.
57 Lee, K.B., S.J. Park, C.A. Mirkin, J.C. Smith, and M. Mrksich. 2002. Protein nanoarrays generated by dip-pen nanolithography. Science 295:1702-1705.
58 Cao, X.A., H. Cho, S.J. Pearton, G.T. Dang, A.P. Zhang, F. Ren, R.J. Shul, L. Zhang, R. Hickman, and J.M. Van Hove. 1999. Depth and thermal stability of dry etch damage in GaN Schottky diodes. Applied Physics Letters 75:232-234.
59 Tanaka, S., Y. Kawaguchi, N. Sawaki, M. Hibino, and K. Hiramatsu. 2000. Defect structure in selective area growth GaN pyramid on (111)Si substrate. Applied Physics Letters 76:2701.