Si/Ge MIST - 7128
Work Area: Microelectronics
Keywords Si/Ge heterostructure system, Si/Ge quantum wells, SimGen strained layer superlattices, Si MBE, characterisation of heterostructures
Start Date: 1 July 92 / Duration: 36 months / Status: running
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Abstract Si/Ge microstructures grown on <100>Si substrates offer the possibility of integrating optical devices (LED and photodiode) with Si-based conventional integrated circuits (ICs). These microstructures have a variety of multifunctional device capabilities (eg SiGe Gunn diode) making use of novel bandstructure effects and transport phenomena in strained Si/Ge heterostructures. Their properties are predicted and investigated with theoretical models and their structural and material properties measured using extensive characterisation techniques. Simple two-terminal devices (eg mesa and waveguide diodes) serve as demonstrators for the device performance capability.
The goal is to study the SiGe heterostructure system with special emphasis on atomically thin layers deposited on an Si substrate by MBE. The project aims to exploitat novel effects and material properties such as optical transitions in the near-infrared regime, strain effects, non-linear optical properties and change of carrier mobility. Simple demonstrator devices showing the performance and characteristics of Si-based optoelectronic devices are planned.
Approach and Methods
The work is divided into the following major tasks:
- Growth of the SiGe microstructures by molecular beam epitaxy (MBE) methods on
<001> Si substrates. The previous ESPRIT Action 3174 led to the growth of superlattices with a period length smaller than the lattice constant of silicon (2 monolayers period L=0.28nm, a0=0.5431nm bulk lattice constant of Si).
- Structural characterisation of the SiGe microstructures by transmission electron microscopy (TEM), X-ray diffraction and Raman spectroscopy.
- Study of the electronic and optical properties of the Si/Ge microstructures by photoluminescence (PL), photoconductivity, absorption and Hall measurements. Also modulation techniques such as photoreflectance and electroreflectance as well as junction space charge techniques such as photocapacitance and short circuit current measurements will be applied.
- Fabrication and characterisation of mesa and waveguide diodes as test vehicles for novel SiGe devices. The electrical characteristic of Si/Gep-n junctions (I-U and C-U curves) will state the progress in the material growth, device technology and functions. Optical responsivities or electronic transport times will be measured and compared with existing Sidevices.
- Achievement of the qualitative and quantitative understanding of the electronic bandstructure of the SimGen superlattices, Si/Ge and Si/Si1-xGex quantum well structures and Si1-xGex alloy layers based on ab initio and empirical pseudopotential calculations. Also an understanding of the microscopic mechanism of the SiGe growth and interface formation especially under MBE growth conditions. The influence of various parameters such as substrate temperature, growth rate, dopant incorporation and surface segregation on the grown layer quality will be studied theoretically and compared with experiment. Special emphasis will be given to ordering phenomena during growth.
- Search for novel effects and their possible applications. It is planned to study inter sub-band and miniband absorption to extend the possible wavelength range to the mid- infrared region. In addition we plan to examine nonlinear optical effects.
Progress and Results
Major achievements so far are:
- Growth of a Si17Ge2 SL on Si substrate (pseudomorphic growth) with sub-monolayer interface sharpness.
- Substantial improvement of material quality by applying the technique of "surfactant" growth in terms of interface sharpness, reduction of defect density and planarity of grown layers.
- Breakthrough in buffer quality in terms of reduction of threading dislocation (TD) density and improvement of material quality by growth of a Ge graded Si1-y(z)Gey(z) buffer layer followed by a constant composition, fully relaxed Si1-yGey buffer layer [H.Presting, H.Kibbel, Thin Solid Films 222, 215 1992].
- Strong PL signals observed in the near-infrared regime (0.75 eV < hv < 0.85 eV; (1.45 micron < lambda <1.65 micron).
- Shift of PL wavelength as a function of SL composition in agreement with expected behaviour of quasi direct transition [U.Menczigar et al., Phys.Rev. B47, p.4099 1993].
- First room-temperature electroluminescence from a strain-symmetrised Si6Ge4 SL diode [J.Engvall et al., Appl.Phys.Lett. 63 (4), 1993].
- Theoretical understanding of interface stability and ordering effects (Sb as surfactant) [P.C.Kelires et al., submitted to PR B, 1993].
- Theoretical investigation of novel Si/Ge QW structures with large optical oscillator strength in the near-infrared and simpler growth structure [K.B.Wong and M.Jaros, to be published, 1993].
- Study of non-linear and electric field induced properties of Si/Ge QWs and SimGen SLS.
- Observation of inter sub-band transitons in the far-infrared regime (10 micron < lambda < 15 micron) from pseudomporphically grown as well as strain-adjusted Si/Si1-xGex QWs.
- Evaluation of strain and composition of a relaxed Si1-yGey buffer layers by reciprocal space mapping in the TAD analysis of a strain-adjusted SimGen SL.
In general, the Si/Ge microstructure system can serve as model system to study strain effects, mismatch accomodation and growth techniques for other strained heterostructure systems. The results obtained here for growth parameters, characterisation techniques and numerical tools for calculating the bandstructure of SiGe microstructures are of broad usage and can be applied in other heterostructure systems such as for example in the III-V material area (egInGaAs/GaAs) as well.
- Presting H and Kibbel H Buffer Concepts of Ultrathin SimGen Superlattices Thin Solid Films 222, pp. 215-220, UNC (1992)
- Jaros M, Beavis A W, Hagon P J, Turton R J, Miloszewski A and Wong K B Quantitative theory of optical properties of Si-Ge heterostructures Thin Solid Films 222, pp. 205-208 (1992)
- Brunner J, Menczigar U, Gail M, Friess E and Abstreiter G Band gap luminescence in pseudomorphic Si1-xGex quantum wells grown by molecular beam epitaxy Thin Solid Films 222, pp. 27 (1992) 27
- Menczigar U, Abstreiter G, Kibbel H, Presting H, Kasper E, Olajos J, Grimmeiss H G Enhanced band-gap luminescence in strain-symmetrised (Si)n/(Ge)n superlattices Phys. Rev. B 47, pp. 4099 (1993)
- Theodorou G, Tserbak C and Polatoglou H L Electronic properties of strained Si/Ge superlattices: tight binding approach Thin Solid Films 222, pp. 209 (1992)
- Engvall J, Olajos J, Grimmeiss H G, Presting H, Kibbel H and Kasper E Electroluminescence at room temperature of a SinGem strained layer superlattice Appl. Phys. Lett. 63 (1993)
- Frommherz T, Helm M, Bauer G, Kibbel H and Kasper E In-plane and vertical high frequency conductivity in SiGe short period superlattices Thin Solid Films 222, pp. 251-53 (1992)
Information Dissemination Activies
Conferences: NATO ARW, Riva Sept. 92; 21th ICPS Beijing, China, 8/92; Symposium "Si-based heterostructures", AVS Meeting, Chicago 11/92; Spring Meeting of MRS, Symposium "Si-based optoelectronic materials", San Francisco, 4/93; Modulated Semiconductor Structures , Garmisch-Partenkirchen, 8/93. Two symposia and conferences on related topics have been organised by partners of this research action :
- Kasper E., Symposium A of EMRS Spring Meeting 1992, SiGe based Heterostructures. Strasbourg (France) 1992.
- Abstreiter G., Sixth International Conference on Modulated Semiconductor Structures, Garmisch-Partenkirchen (Germany), 1993.
Daimler-Benz AG (DB) - D
Research Center Ulm
Wilhelm-Runge Str. 11
D - 89081 Ulm
University of Newcastle (UNC) - UK
Technische Universität München (TUM) - D
Foundation of Research and Technology-Helas (FORTH) - GR
University of Lund - S
Universität Linz - A
Dr. H. Presting
tel +49/731 505-2049
fax +49/731 505-4102
Si/Ge MIST - 7128, August 1994
please address enquiries to the ESPRIT Information Desk
html version of synopsis by Nick Cook