Investigation of energy transfer between europium centers in GaN:Eu using combined excitation emission spectroscopy

摘要

Establishing an all GaN based red LED is animportant step toward micro-LED displays,which are the next step in a rapidly growing“smart society”. Since commerciallyavailable red LEDs are achieved usingAlGaNInP/GaAs, we have been working on aGaN:Eu based LED. Europium is a rare-earth,characterized by intrinsic 4f transitions,allowing for a temperature and hostindependent emission at ～620 nm. However,due to its size, Eu can create different defectenvironment in the GaN host. Using combinedexcitation emission spectroscopy (CEES), wehave established the existence of 8 differentemission centers in our organometallic vaporphase epitaxy (OMVPE) grown samples. Wehave also determined the proportion of eachcenters and their efficiency. The two maincenters are called OMVPE4 (most abundant)and OMVPE7 (most efficient). CEES is therecord of the photoluminescence (PL) as theexcitation energy is changed by using a dyelaser, while the PL is recorded with a CCDequippedmonochromator. To gain a morefundamental understanding of the energytransfer between the defect levels in the hostand the OMVPE4 and OMVPE7 Eu centers, atwo laser experimental setup was designed. Inthis set-up, one laser is used to directly exciteeach Eu center individually, and another isused to excite other defect levels within theGaN host, which can in turn transfer energy tothe Eu centers. Preliminary results indicatethat a direct excitation of OMVPE4 can lead tothe emission from OMVPE7 via a transfer ofenergy through the host. In this contribution,we will further explore the nature of this energytransfer using our two laser excitationexperiment, and discuss its possible influenceon the operation of GaN:Eu based red LEDs.