HAL Id: jpa-00226692
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Submitted on 1 Jan 1987
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THE ROLE OF STRAIN AND SURFACE STOCHIOMETRY IN THE SYNTHESIS OF InAs/GaAs (100) MULTILAYER COMPOUNDS
F. Grunthaner, J. Liu, B. Hancock
To cite this version:
F. Grunthaner, J. Liu, B. Hancock. THE ROLE OF STRAIN AND SURFACE STOCHIOMETRY IN THE SYNTHESIS OF InAs/GaAs (100) MULTILAYER COMPOUNDS. Journal de Physique Colloques, 1987, 48 (C5), pp.C5-75-C5-76. �10.1051/jphyscol:1987511�. �jpa-00226692�
JOURNAL DE PHYSIQUE
Colloque C5, suppl6ment au noll, Tome 48, novembre 1987
THE ROLE OF STRAIN AND SURFACE STOCHIOMETRY IN THE SYNTHESIS OF InAs/GaAs ( 1 0 0 ) MULTILAYER COMPOUNDS
F.J. GRUNTHANER, J.K. LIU and B. HANCOCK
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, C A 91109, U . S . A .
Lattice-mismatched or strained-layer epitaxy is a particularly intriguing problem because of the promise of new materials systems and novel electronic properties derived from strain- induced modification of local structure. In addition to the interest in strained-layer systems related to the development of new electronic and optoelectronic devices, the study of the dynamics of their growth using MBE promises to strongly enhance our understanding of III- V MBE growth mechanisms. Using our RHEED controlled growth techniques, we find that in the InAs/GaAs system these materials grow in registration to the substrate, giving rise to a tetragonal distortion of the local coordination. This modification of the bonding and symmetry of t h e growing film has serious ramifications for the physisorbed and chemisorbed species which establish the growth front and the surface stochiometrym. The surface transport of In or Ga, the chemical incorporation of As2 or As4 and the details of the terrace and step distributions all show a sensitivity to bond strain and lattice mismatch. The interfacial roughness of heterojunction boundaries in these superlattice systems is likewise affected by local strain and potential variations.
In this paper, we address the issues of strain and surface stoichiometry and their effect on the growth kinetics of InAs/GaAs superlattices grown on GaAs<100> substrates through an analysis of Reflection High Energy Electron Diffraction. Using a digitized video system to record RHEED patterns during film growth, we analyze the diffraction on a frame-by-frame basis. This permits a continuous description of the surface lattice constant of the growing film and the intensity modulation along a diffraction streak. Each RHEED pattern corresponds to the deposition of 0.01 monolayers of material. We demonstrate that the surface lattice constant is a function of film converage, temperature and the relative fluxes of Group I11 and Group V components which control the dynamic surface stoichiometry. Under conditions which approximate bilayer deposition, the InAs layers give surface lattice constants identical to the bulk GaAs substrate. We observe a sharp transition of the surface lattice constant with a period corresponding to integral monolayer coverage of 1nAs. Under As-rich conditions, extensive dislocations are generated, relieving the strain and giving rise to an lnAs surface lattice constant identical to the bulk lnAs value. Under In-stabilized conditions, we observed both pseudomorphic and unstrained material simultanenusly within !he coherence length of the RHEED. This two phase region and the reIative spatial extent of each growth region is directly related to surface stochiometry. Using our growth interruption technique we observed
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987511
C5-76 JOURNAL DE PHYSIQUE
dislocation densities f o r inAslGaks superlattices of 10 t o 100 per cm2 when t h e thickness of t h e GaAs layers a r e equal t o twice t h a t of t h e InAs layers of t h e superlattice. For continuous growth, we find densities of 104 t o 105 per cm2. These observations a r e interpreted in t e r m s of a model which explicitly t a k e s into account t h e contribution of strain t o t h e kinetic processes a t t h e growth front and some of t h e s t r e s s induced ramifications f o r t h e extended i n t e r f a c e s of t h e superlattices. Finally, we describe t h e unique stability of these s t r u c t u r e s in t e r m s of t h e synthesis of a new crystal s t r u c t u r e consisting of highly perfect interlayers t h e binary components giving a structural formula ( l n A ~ ) ~ ( G a A s ) ~ , where b>a, and both a band b a r e integers taking values less than 10.
This work is supported by NASA, ISTC-SDI0 and ONR a t JPL.
