PUMA
Istituto dei materiali per l'elettronica ed il magnetismo     
Frigeri C., Grillo V., Shakhmin A. A., Vinokurov D. A., Zamoryanskaya M. V. Chemical characterization of extra layers at the interfaces in MOCVD InGaP/GaAs junctions by electron beam methods. In: E-MRS Fall Meeting 2010 - Multidimensional Electrical and Chemical Characterization at the Nanometer-scale of Organic and Inorganic Semiconductors - Symposium D (Varsavia (PL), 13-17 Sept. 2010). Abstract, p. 3-4. E.MRS, 2010.
 
 
Abstract
(English)
InGaP/GaAs heterostructure is known to suffer interface roughness over some monolayers which leads to formation of an extra layer at the interface chemically different from InGaP and GaAs. Such extra layer can recombine the minority carriers more efficiently than the GaAs quantum well. This work is a contribution to the identification of such extra layer in InGaP/GaAs heterojunctions grown on GaAs substrate by low pressure MOCVD by means of spectral cathodoluminescence (CL) at 77 K, and chemically sensitive TEM methods, i.e., (200) dark field (DF) and High Angular Annular Dark Field (HAADF), and High Resolution TEM. After a GaAs buffer the sample consisted of an InGaP layer nominally followed by a 10 nm thick GaAs layer capped with AlGaAs. CL did not reveal the 10 nm GaAs QW layer. Instead, an unwanted quaternary layer of composition In0-0.15GaAsP0.02 was detected. Both (200) DF-TEM and HAADF contrast at the location of the nominal 10 nm thick GaAs layer confirmed that no GaAs is there. Theoretical calculation of the (200) DF contrast suggested that such layer can be InxGa1-xAs1-yPy for composition values of x and y that agree with the composition estimated by CL. This is also concluded from HAADF results by assuming the Z2 dependence of the contrast and by strain analysis at the GaAs-on-InGaP interface by HR-TEM. It is hypothetized that the first step for the creation of the quaternary InGaAsP layer could be the formation of GaAsP by P/As intermixing at the GaAs-on-InGaP interface made possible by the expected presence of residual P atoms when the As flux is switched on. The tensile strain field associated with GaAsP can be the driving force for In incorporation as large atoms easily segregate in regions of high tensile strain and therefore InGaAsP is formed.
Subject InGaP/GaAs
Interface
Chemical composition
Electron beam methods


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