Luminescence of TM 3+ in Gallium Arsenide Grown by Metal-Organic Vapor Phase Epitaxy
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LUMINESCENCE OF TM 3+ IN GALLIUM ARSENIDE GROWN BY METAL-ORGANIC VAPOR PHASE EPITAXY ACHIM DORNEN, KLAUS PRESSEL*, CHRISTOPH HILLER, DIETER HAASE, JURGEN WEBER,*- and FERDINAND SCHOLZ 4. Physikalisches Institut, Universitit Stuttgart, D-W-7000 Stuttgart 80, Box 80 11 40, Federal Republic of Germany *now with: Institut fuir Halbleiterphysik, D-O-1200 Frankfurt/Oder, Walter-Korsing-Str. 2, Federal Republic of Germany **now with: ALCATEL-SEL Research Center, ZFZ1 WO, Lorenzstr. 10, D-W-7000 Stuttgart 40, Federal Republic of Germany ABSTRACT 3 We investigate the excitation mechanism of the characteristic 4f luminescence H 5 This luminescence photoluminescence excitation spectroscopy. 'H6 of TmS+ in GaAs by transition is also used to study the incorporation of thulium into the GaAs lattice by angular dependent Zeeman spectroscopy.
INTRODUCTION When thulium is introduced into various host crystals a characteristic 4f luminescence at 1.2 pm (1.0 eV) and 1.9 pm (0.68 eV) can be observed [1]. This emission is due to the Tm3+ 2 charge state. The Tm3+ ion has a 4f" electron configuration. By spin orbit coupling the electronic ground state (L = 5, S = 1) is threefold split into the 3 H6 , 3 IH4, and 3 H5 levels. The latter two are separated from the 3 H6 ground state by 0.68 and 1.0 eV, respectively. In III-V semiconductors each level is additionally split by the tetrahedral crystal field, when the ion occupies a simple substitutional lattice site. The electric dipole transitions uH5-- 'H6 and 'H4__-3 H6 then give rise to both luminescence bands. The luminescence of Tm3+ in III-V semiconductors has recently been observed after Tm implantation by G. Pomrenke and coworkers [2, 3] and after doping during metal-organic vapor phase epitaxy (MOVPE) by K. Pressel et al. [4]. The intention of the present work is to investigate the lattice site on which Tm is incorporated into GaAs. For this purpose angular dependent Zeeman measurements on the 3H5 -_* 3 H6 1.0-eV luminescence were carried out. Another topic of the present study focusses on the excitation mechanism and the excitation efficiency of the characteristic 4f luminescence transitions 3 H5 --- 3H6 at 1 eV. EXPERIMENTAL For photoluminescence measurements the samples were excited by the 647 nm line of a krypton-ion laser. The light was dispersed with a 3/4m Spex grating monochromator and detected by a high sensitive Northcoast germanium detector. When high sensitivity was required a BOMEM DA3.01 Fourier spectrometer was used instead of the grating monochromator. Photoluminescence excitation (PLE) spectra were recorded by using a Titanium/sapphire laser which is tunable from 1100 to 700 nm wavelength. All PLE spectra were corrected for the spectral response of the laser. Zeeman measurements were carried out with a 3/4m Spex grating monochromator. Magnetic fields up to 7.5 T could be applied with a split-coil magnet, allowing measurements in Voigt and Faraday configuration (perpendicular and parallel to the magnetic field), respectively. The samples were grown by MOVPE using Tris(
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