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ELECTRICAL AND OPTICAL PROPERTIES OF Yb, Er doped GaAs

T.BENYATrOU*, D. SEGHIER*, G. BREMOND*, S.MONEGER*, A. KALBOUSSI*, G. MARRAKCHI* AND G. GUILLOT*, C. LHOMER* *, B. LAMBERT**, Y. TOUDIC** AND A. LE CORRE ** *INSA de Lyon, Bit 502, LPM URA CNRS 358, 20 Av Albert Einstein 69621 Villeurbanne C&lex France

**CNET/LAB/OMC/MPA, 22301 Lannion, France

ABSTRACT In this paper we report results from electrical and optical measurements carried out on GaAs:Yb, Er. For GaAs:Yb electrical experiments such as photoconductivity (PC) and Photo Induced Current Transient Spectroscopy (PICTS) show that there is a level at 0.65eV related to Yb. This explains why no Yb 3 + photoluminescence (PL) emission is detected, the recombination energy of the trapped

excitons is too low (- 0.6eV) to excite the Yb3 + internal transition(- 1.24eV). We also present results on Er doped GaAs materials. From PL experiments we deduce an estimate of 1019 cm 2 'for the stimulated emission cross section. By PICTS and PC, we have evidenced a trap at 0.67eV related to Er ions in GaAs. And we think that in this case, the rare earth ions are excited via formation of bound excitons.

INTRODUCTION Rare earth (RE) doped 11I-V materials are very attractive for new emitting device applications such as lasers and LEDs [1-6]. In this case, the emission is no more based on band to band recombination but on the internal emission of the doping ions. Among them, Er 3 + is very promising because of its 1.54 jam emission which is well adapted to silica based optical fiber telecommunication. However, electrical properties of these systems are not fully understood as well as their relations to the optical activity of the RE impurity. In order to improve our understanding of the RE excitation mechanism, we have carried out photoluminescence (PL), photo-induced current spectroscopy (PICTS), and photoconductivity (PC) measurements on Er, Yb doped GaAs materials.

EXPERIMENTAL Yb-doped GaAs epitaxial layers have been successfully obtained by the gas MBE technique at

Centre National d'Etude des T6l6communications. A gaseous source ( AsH3 ) was used to obtain the V element and a solid source to obtain the RE element (Yb). A 1.2 pm thick layer was grown on a semi-insulating GaAs substrate with a growth rate of about 1 jm h-1 . Yb concentration measured by 3 Secondary Ion Mass Spectroscopy (SIMS) in the layer was found to be 2 x 1017 cm- . SIMS analysis also indicated the poor quality of the Yb source (4N) since metallic impurities such as Si, Ca,

and Mg were detected in the sample with concentrations below 1016 Cm-3 . At room temperature the sample is semi-insulating. Details concerning the growth technique are reported elsewhere [7M. Er-doped GaAs samples have been grown in the Laboratoire Central de Recherche of

THOMSON-CSF, by MBE. All details concerning the growth technique are reported in the reference[81.

The PL measurements were carried out using a 5145 A line of argon ion laser with a power of 200 mW focused on a 150 jm diameter Spot. The PL signal was detected wi