Si-SiGe Quantum Dot-Based Light Emitting Diodes
With the reduction of the minimum feature size in semiconductor microelectronics, more and more information can be stored in a unit area on a microchip. The speed and capacity of digital information transfer will soon be limited by the electrical connections on the chips as well as on the board level. This requires the development of a faster and low cost technology such as so called 'optical interconnects'. As we know, the dominant material used in the microelectronics industry is silicon, which is no good for optoelectronic devices due to its indirect bandgap, while most of the light emitting devices are based on III-V compounds, which are technologically incompatible with Si-technology. Our need here is an effecient light emitting device which could be monolithically integrated into Si-microchips using Si-technology. This has led to extensive studies of the ultrathin In our pioneering work on Si-SiGe nanostructrues, we have found that when a Si-SiGe superlattice is cut into quantum dots of less than about 100nm diameter, the optical efficiency can be improved by over two orders of magnitude, which is likely originated from process-induced strain and lattice structure change, which is supported by optical and synchrotron sourced X-ray diffraction experiments, and should be interesting for both physics studies and device applications. Recently, we have used our finding and fabricated the world's first Si-SiGe quantum dot-based light emitting diodes, and observed efficient ROOM TEMPERATURE electroluminescence from them (see diagram). Such devices may be ideal in fulfilling the role of light source in the optical interconnects which could be directly integrated into Si-chips.
(m+n=10) superlattices which were theoretically predicted to have pseudo-direct bandgap. Here in Glasgow, we have taken another approach, i.e., using artificially fabricated small Si-SiGe quantum dots.
We are currently working on both the physical origins of the phenomenon and the device technology aspects, and intend to fabricate a Si-based monolithic integrated unit suitable for the microelectronics industry in the future.
[1] Y.S.Tang, C.M.Sotomayor Torres, R.A.Kubiak, T.E.Whall, E.H.C.Parker, H.Presting & H.Kibbel, 'Photoluminescence and photorelectance study of Si/SiGe quantum dots' presented at the 36th Int. Conf. on Electron. Mater., Colorado, June 1994; and J. Electron. Mater. 24, 99(1995)
[2] Y.S.Tang, C.M.Sotomayor Torres, S.Nilsson, B.Dietrich, W.Kissinger, T.E.Whall & E.H.C.Parker, 'Photoluminescence and Raman spectroscopy of Si-SiGe quantum dots' presented at the 95ÔSi-MBE, France, May 1995; and J. Cryst. Growth 157, 280(1995)
[3] Y.S.Tang, C.M.Sotomayor Torres, B.Dietrich, W.Kissinger, T.E.Whall & E.H.C.Parker, 'Raman sepctroscopy of dry etched Si-SiGe quantum dots' Solid State Commun. 94, 369(1995)
[4] Y.S.Tang, C.M.Sotomayor Torres, T.E.Whall, E.H.C.Parker, H.Presting & H.Kibbel, 'Optical properties of Si-SiGe and Si-Ge nanostructures ' J. Mater. Sci.: Materials for Electronics 6, 356(1995)
[5] Y.S.Tang, C.M.Sotomayor Torres, S.Nilsson, B.Dietrich, W.Kissinger, T.E.Whall, E.H.C.Parker, H.Presting & H.Kibbel, 'Residual strain in Si-SiGe quantum dots' presented at the 7th Int. Conf. on Modulated Semiconductor Structures, Madrid, Spain, Sept. 1995; and Solid State Electronics (1995) (in press)
[6] Y.S.Tang, W.X. Ni, C.M.Sotomayor Torres & G.V.Hansson, 'Fabrication and characterisation of Si-SiGe quantum dot light emitting diodes' Electron. Lett. 31, 1385(1995)
[7] Y.S.Tang, C.M.Sotomayor Torres, et al, 'Elastic strains in dry etched Si-SiGe quantum dots' presented at the 37th Int. Conf. on Electronic Materials, Viginia, USA, June 1995J. Electron. Mater. 25, 287(1996)
[8] Y.S.Tang, W.X.Ni & C.M.Sotomayor Torres, 'Photoluminescence and electroluminescence study of Si-Si0.7Ge0.3 quantum dots' presented at the Int. Symp. on 'Si Heterostructures: From Physics To Devices', Crete, Greece, Sept. 1995; and Appl. Surf. Sci. (Jan. 1996) (in press)
[9] Y.S.Tang & C.M.Sotomayor Torres, ' An analysis of residual strain in semiconductor nanostructures' presented at the 95ÕGADEST, Berlin, Germany, Sept. 1995; and Proceedings in Solid State Phenomena 47-48, 613(1996)
[10] C M Sotomayor Torres, P D Wang, N N Ledentsov and Y-S Tang, 'Luminescence from semiconductor quantum wires and dots: bottleneck and localization issues', Proc. 13th Pfefferkorn Conference on Luminescence in Niagara Falls, Canada, 13-18 may 1994
[11] Y.S.Tang, C.M.Sotomayor Torres, R.A.Kubiak, T.E.Whall & E.H.C.Parker, 'High efficiency optical emission in Si/SiGe quantum dots' Presented at the 1993 Condensed Matter and Materials Physics Conference (CMMP-93), Leeds, Dec. 1993 (Late News)
[12] Y.S.Tang, C.M.Sotomayor Torres, C.D.W.Wilkinson, D.W.Smith, R.A.Kubiak, T.E.Whall, E.H.C.Parker, H.Presting & H.Kibbel, 'Optical emission from Si/SiGe quantum wires and dots' Proc. of 22nd Int. Conf. on Phys. of Semicond., Vancouver, Aug. 1994, ed. by D.J.Lockwood (World Scientific, Singapore, 1994) p.1735
[13] C.M.Sotomayor Torres, P.D.Wang, Y.S.Tang & N.N.Ledentsov, 'Quantum Dots for optoelectronics ' IEE Colloquium on 'Micro-engineering and Optics' (Digest No. 1994/043) (IEE, London, 1994), p.3
[14] B.Dietrich, Y.S.Tang & C.M.Sotomayor Torres, 'Comparison of strain in Si/SiGe pseudomorphic heterostructures and quantum dots' 95ÕGADEST, Berlin, Germany, Sept. 1995
[15] Y.S.Tang, W-X Ni & C.M.Sotomayor Torres, 'Si-SiGe quantum dot light emitting diodes' 2nd ECAMI workshop (ESPRIT sponsored collabrotaion between PHANTOMS and the NRC), Glasgow, Aug. 1995
[16] C.M.Sotomayor Torres & Y.S.Tang, 'Emissions from Si-SiGe quantum dots' (invited talk) N=N UK-Japan Workshop on Nanostructure Physics and Technology, Thornbridge, UK, 12-14 August 1995
[17] Y.S.Tang, W.X.Ni, C.M.Sotomayor Torres & G.V.Hansson, 'Photoluminescence and Electroluminescence of Si-Si0.7Ge0.3 quantum dot diodes' 188th Meeting of the Electrochemical Society: Luminescent and Display Materials, Chicago, USA, Oct. 1995; in Advanced Luminescent Materials, edited by D.J.Lockwood (Electrochem. Soc. Pennington Press, USA, 1996)
[18] Y.S.Tang, W.X.Ni, C.M.Sotomayor Torres & G.V.Hansson, 'Si-Si0.7Ge0.3 quantum dot based light emitting diodes' PHASDOM'95, Cambridge, Oct. 1995
[19] Y.S.Tang & C.M.Sotomayor Torres, 'Damage, strain and quantum confinement issues in dry etched semiconductor nanostructures' 1995 MRS Fall Meeting, Boston, Nov. 1995; to appear in 'Surface/Interface and Stress Effects in Electronic Material Nanostructures', Eds S M Prokes, R C Cammarata, K L Wang and A Christou, MRS Proc. (Pittsburgh, PA, USA) Vol 405, (1996)
[20] Y.S.Tang, C.M.Sotomayor Torres,W.-X.Ni,G.V.Hansson and S.P.Beaumont, "Optical properties of Si-Si1-xGex quantum dots and anti-dots" Accepted to 23rd Int. Conf. on Phys. Semicond., July 1996, Berlin, Germany
[21] Y.S.Tang, S.E.Hicks, C.M.Sotomayor Torres, C.D.W.Wilkinson, W.-X.Ni and G.V.Hansson, "Light emission from Si-Si1-xGex quantum dots coated with stressed SiNx", Accepted to 23rd Int. Conf. on Phys. Semicond., July 1996, Berlin, Germany
[22] Y.S.Tang,S.E.Hicks,W.-X.Ni,C.M.Sotomayor Torres,G.V.Hansson and C.D.W.Wilkinson, "Improving process stability and light emission from Si-Si1-xGex quantum dot diodes", Submitted to 54th Annual DRC, June 1996, Sanda Barbara, USA
[23] Y.S.Tang,S.E.Hicks,W.-X.Ni,C.M.Sotomayor Torres,G.V.Hansson and C.D.W.Wilkinson, "Controlling the strain and light emission from Si-Si1-xGex quantum dots", Invited Contribution to 1996 E-MRS Spring Meeting, June 1996, Strathboug, France
[24] W.-X.Ni, J.Birch, Y.S.Tang, K.B.Joelsson, C.M.Sotomayor Torres, A.Kvick & G.V.Hansson, "Lattice distortion in dry etched Si/SiGe quantum dot arrays studied by 2D-reciprocal space mapping using synchrotron X-ray diffraction", Invited Contribution to 1996 E-MRS Spring Meeting, June 1996, Strathboug, France
[25] Y.S.Tang,C.M.Sotomayor Torres,W.-X.Ni & G.V.Hansson, "Room Temperature Electroluminescence of Nanofabricated Si-Si1-xGex Quantum Dot Diodes" Accepted for NanoMES'96, Sanda Fe, May 1996
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