Energy-Back-Transfer Process in Rare-Earth Doped AlGaN
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Energy-Back-Transfer Process in Rare-Earth Doped AlGaN A.Wakahara, T.Fujiwara, H.Okada, A.Yoshida, T.Ohshima1, and H.Itho1 Department of Electrical & Electronic Engineering, Toyohashi University of Technology, Toyohashi 441-8580, JAPAN 1 Department of Material Development, JAERI-Takasaki, Takasaki, 370-1292, Japan ABSTRACT Temperature dependence of time-resolved photoluminescence (PL) properties for rare-earth ions (REIs: Eu, Tb, and Er) implanted AlxGa1-xN (x=0~1) is investigated. Thermal quenching for RE-related PL becomes small when increasing the Al contents. The PL decay time of REIs used in the present work becomes shorter when increasing the temperature and/or PL peak energy. The temperature dependence of PL intensity and the decay time are analysed by assuming phonon assisted energy-back-transfer model, in which the energy in REIs escape to trap levels. From the results, the improvement of PL properties can be well explained by the model, in which the activation energy for energy-back-transfer process is increased as increasing the Al contents. INTRODUCTION Light emission from rare-earth ions (REIs) in a semiconductor has been paid much attention in order to realize a temperature stable light emitting device for optoelectronic systems, because 4f-4f electron level transitions in REIs have narrow bandwidth and less temperature sensitive peak position [1]. Recently, room-temperature operation of injection type light emitting diode was achieved by using GaAs simultaneously doped with Er and O [2]. However, thermal quenching REIs-related photoluminescence (PL) in conventional semiconductors, such as Si and GaAs, is large because of relatively narrow band-gap. Recent progress in III-nitride leads to studies of REIs doped GaN, and some research groups reported on development of visible electroluminescent devices [3-5]. Recently, it is found that PL properties of REIs (Eu, Tb, Tm, and Er) in AlxGa1-xN are strongly affected with the AlN molar fraction [6-11]. The PL intensity related to RE3+ increases with increasing the AlN molar fraction and the thermal quenching is also improved. The results suggest that there is a possibility to improve the luminescence efficiency due to REIs and/or suppression of energy back-transfer rate. However, there are only a a few reports on the effects of AlN molar fraction on the REIs related photoemission, and thus effect of AlGaN on the energy-transfer and/or back-transfer processes is not deeply understood. In this study, we investigated time-resolved photoluminescence to clarify the energy-back-transfer process in AlGaN with various AlN molar fractions. EXPERIMENTAL DETAILS Eu, Tb, and Er were used in the present work. These were implanted into AlxGa1-xN (0≤x≤1) epitaxial layers, which were grown on a sapphire (0001) substrate with a 2µm-thick GaN epitaxial template. The ion implantation was carried out at room temperature with the acceleration energy of 200keV. The dose of the implanted REIs was set to 1×1015cm-2. The project range and peak concentration estimated by using
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