Radiative and Non-Radiative Recombinations at Er Centers in GaAlAs
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RADIATIVE AND NON-RADIATIVE RECOMBINATIONS AT Er CENTERS IN GaA1As TAHA BENYATTOU *, DJELLOUL SEGHIER* AND GERARD GUILLOT * RICHARD MONCORGE** PIERRE GALTIER*** AND MARIE-NOELLE CHARASSE ***
INSA de Lyon, LPM,Bat 502, 69621 Villeurbanne cedex, France. **UCB,Bat 205,Laboratoire de Physico-Chimie des Mat6driaux Luminescents,69622 Villeurbanne cedex,France *
** *Thomson CSF/LCR, 91404 Orsay cedex, France.
ABSTRACT Photoluminescence (PL) of Molecular Beam Epitaxy grown Er doped Ga0.5 5 A10 .45 As has been studied under continuous and pulsed laser excitation. The observdPL lines are attributed to4 transitions from the first excited state 4 113/2 to the ground state 41 15/2. The life time of the 1132 level is found to be 1 ms at 10K, which is comparable to the decay time observed in insulators. Using two-beam experiments we show that there are losses (Auger effect) that occur during the PL excitation.We propose the following model for the Er PL excitation process: excitons bound to Er are created and decay non radiatively by energy transfer to the rare earth (which is the cause of the Er related PL) or to free carriers by Auger effect (which is the cause of the observed losses). INTRODUCTION Incorporating rare earth (RE) in Ill-V compounds is very interesting because of their internal transitions which give rise to narrow emission lines in the near infrared region that are practically independent of the III-V host. In particular, erbium doping [1- 7] seems very attractive due to the possibility of realising new emitting devices at 1.54 gim which corresponds to a minimum of absorption of silica based optical fibers. However, there is a poor knowledge of the excitation-deexcitation processes of these luminescent centers. The aim of this work is to
investigate these processes with PL and two-beam experiments. We propose a simple PL excitation model which accounts for the observed experimental results and show that Auger losses [8] are predominant. MATERIAL AND TECHNIQUES Our study was made on one sample of Gao. 5 5 AI0. 4 5 As doped with an Er concentration
of 3xl0 17 cm- 3 . It was grown by Molecular Beamr Epitaxy at the Laboratoire Central de Recherche THOMSON CSF. Details concerning the growth technique used here are reported elsewhere [5]. For the PL study the excitation was provided, in the CW excitation experiments, by the 5145A line of an Argon ion laser or the 6328A line of an He-Ne laser. The luminescence was then analysed through a 0.6m JOBIN YVON HRS2 monochromator and detected with Ge photodetector cooled to 77K coupled to a lock-in amplifier. Pulsed excitation experiments were also performed. For that we used a YAG : Nd pumped dye laser from QUANTEL which delivered excitation pulses of 15ns duration at 6200A . The PL signal was selected through an adapted broad band interferential filter (X=1.545 +0.024 tim) and detected with a fast response Ge photodetector cooled to 77K. The signal was then analysed with a digital oscilloscope. EXPERIMENTAL DATA Figure 1(a) shows the PL spectrum recorded at 10K under CW
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