Erbium Doped Gallium Arsenide a Self-Organising Low Dimensional System
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ERBIUM DOPED GALLIUM ARSENIDE A SELF-ORGANISING LOW DIMENSIONAL SYSTEM A.R.PEAKER*, H.EFEOGLU*, J.M.LANGER**, A.C.WRIGHT***, I.POOLE* AND K.E.SINGER* Centre for Electronic Materials and Electrical Engineering &Electronics Department, UMIST, Manchester, M60 1QD, England ** Institute of Physics, Polish Academy of Science, Al Lotnikow 32/46, Warsaw 02668, Poland ***Advanced Materials Laboratory, North East Wales Institute, Connah's Quay, Wales *
ABSTRACT
The growth of erbium doped gallium arsenide by MBE at normal substrate temperatures (-580"C) is constrained by a solubility limit of 8x1 017 cm-3 . This is much less than is desirable for optical emitters using the forbidden 4f transitions of Er3+ to produce radiation at 1.54pm. We have developed an MBE technique where it is possible to produce spherical mesoscopic precipitates containing erbium as a matrix element within the gallium arsenide. Structural and analytical studies indicate that the precipitate is cubic (rock salt) erbium arsenide. The physical size of the precipitates is self limiting as a result of surface migration occurring during MBE growth. By adjusting the growth conditions it is possible to produce an array of uniform erbium arsenide quantum dots of a size chosen from the range 10-20A. The dot density can be varied by changing the erbium flux. INTRODUCTION
Semiconductors doped with rare earths can provide temperature insensitive luminescence with narrow, almost atomic-like, linewidths. This is because the luminescence derives from the internal f shell transitions which are well screened from the matrix lattice. As a result the emission is almost host independent. Erbium is of particular interest because it has a characteristic emission at 1.54pm which is near to the minimum absorption window of silica-based optical fibres. A wide variety of experimental techniques, including liquid phase epitaxy (LPE)1, ion1 implantation2,2 metal or4ganic chemical vapour deposition (MOCVD) 3 and molecular beam epitaxy (MBE) 4'., have been employed to incorporate erbium into the binary semiconductor gallium arsenide. For the latter technique, optimum growth conditions and erbium concentrations for maximum luminescence efficiency have been deduced 4, but few structural studies have been undertaken. Using MBE we have grown and undertaken detailed structural characterisation of gallium arsenide doped with erbium in the range 4 x 1016 cm 3 to 2 x 1020 cm3. Secondary ion mass spectroscopy (SIMS) has been used to study the concentration of erbium incorporated into gallium arsenide as a function of both substrate and erbium cell temperature. Transmission electron microscopy (TEM) has been used to determine the concentration, size and chemical composition of erbium-related microprecipitates present in the gallium arsenide doped with erbium at concentrations beyond the solubility limit. Mat. Res. Soc. Symp. Proc. Vol. 301. ©1993 Materials Research Society
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EXPERIMENTAL [Er) SIMS cmr-
The samples were grown ina RIBER 2300 2 X 10'8 MBE system employing conventional t
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