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EXCITATION AND RELAXATION PROCESSES OF IMPACT EXCITATION EMISSION OF Er3+ IONS IN InP T. KIMURA, H. ISHIDA, S. YUGO, R. SAITO, H. ISSHIKI* AND T. IKOMA*° University of Electro-Communications, Department of Electronics Engineering, 1-5-1 Chofugaoka, Chofu-shi, Tokyo 182, Japan, * Frontier System, Riken Institute, 2-1 Hirosawa, Wako-shi, Saitama 351-01, Japan, ** Institute of Industrial Science, University of Tokyo, 7-22-1 Roppongi, Minatoku, Tokyo 106, Japan ABSTRACT Time-resolved excitation and relaxation processes of the impact excitation emission (EL) at 1.54pm of Er 3+ ions doped in InP were investigated in the temperature range from 77K to 330K. The decay process was almost exponential in all the measured temperature range and showed little thermal quenching. The decay time of 2ms at 77K decreased only to tms at 330K. This result contrasted with the large thermal quenching and nonexponential characteristics of the photoluminescence (PL) time decay at higher temperatures, suggesting different Er3+ centers excited between EL and PL. A two-emission-center model is proposed and the different behaviors of thermal quenching and time decay between EL and PL emissions are consistently explained. INTRODUCTION Studies on the emission of rare earth (RE) ions in III-V compounds have mostly been carried out by means of photoluminescence (PL) technique. However, the impact excitation emission (electroluminescence-EL) at 1.54pm of Er3+ ions doped in InP which we have observed for the first time [?],[2] shows different emission characteristics from those of PL emission; little thermal quenching of the EL emission intensity in contrast to strong thermal quenching of PL and different fine structures of PL and EL emission spectra from the same sample. It was considered that Er3+ ions located on different lattice sites were excited between EL and PL. Similar differences have also been presented recently for Er ions doped in MOCVD GaAs [3], and the above characteristics may, therefore, be common to rare earth ions doped in III-V compounds. It is expected that the analysis of the excitation and relaxation processes of EL emission in comparison with those of PL emission will give us some clue to the mechanisms for the excitation and relaxation processes and physical key factors limiting the emission efficiency of RE ions doped in III-V semiconductors. This paper deals with the time-resolved characteristics of the 1.54pm EL emission processes. The temperature dependence of the time decay is presented and the different behaviors of the relaxation process between EL and PL are discussed. A two-emissioncenter model is proposed to explain differences in the relaxation processes between PL and EL.

SAMPLE FABRICATION AND MEASUREMENTS Er ions were implanted into n-type (n ,,• 5 x 10' 5 /cm 3 ) InP at 150 keV to a dose of 7 x 1014 /cm 2 and thereafter annealed at 6000C for 20 hrs in a quartz ampoule with As over pressure. Au/Sn ohmic contacts were evaporated and alloyed on both surfaces. As the Er+-implanted region became high resistive, the