High Temperature Photoluminescence and Photoluminescence Excitation Spectroscopy of Er Doped Gallium Nitride
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hosts. An important step forward in the field of Er doped semiconductors was the observation that the room-temperature Er 3÷ photoluminescence (PL) intensity strongly depends on the band gap of the host materials. It was found that for larger band gap energy, there is less detrimental temperature quenching of Er 3÷ PL occurring [3]. Therefore, doping Er 3+ ions into wide gap semiconductors is a promising approach to overcome thermal quenching of Er 3÷ PL. Consequently, current research efforts focus on studying Er 3÷ doped into wide bandgap semiconductors [2,4,5]. Among wide gap semiconductors, III-nitrides have received world-wide attention because of applications as blue lasers, flat panel displays, UV detectors as well as high temperature electronic devices [6]. Because of their wide bandgap, Ill-nitride semiconductors are expected to be excellent host for Er 3÷ ions to emit strong 1.54 p.m PL at room temperature. First results on the observation of 1.54 prm photoluminescence from Er implanted GaN and AIN were reported by Wilson et al. [7]. Subsequently, other research groups reported initial results of photoluminescence, cathodoluminescence, and electroluminescence studies of Er implanted GaN 3 [8-12]. Doping Er through ion implantation, however, limits the depth and distribution of Er + ions and can cause significant damage to the host material. Therefore, the goal for practical device applications is to incorporate Er3+ ions during epitaxial growth. First results on doping Er in GaN during growth were recently reported by Mackenzie et al. [13]. In this paper we present results of high temperature photoluminescence and photoluminescence excitation studies of Er implanted GaN and GaN: Er doped during growth by metalorganic molecular beam epitaxy (MOMBE). EXPERIMENTAL PROCEDURES The GaN film used for Er implantation was grown on a sapphire substrate using reactive ionbeam MBE [7]. Er was implanted at an energy of 300 keV and a fluence of 2x1014 cm"2 . Oxygen was co-implanted at an energy of 40 keV and a fluence of 1015 cm 2 . The 40 keV oxygen energy was chosen to overlap the oxygen and erbium implantation profiles. After implantation the sample was annealed at -6500 C for approximately 60 minutes. As previous SIMS data have shown, most of the Er is located within 0.2 ptm of the sample surface [7]. The Er doped GaN film was grown by MOMBE in an INTEVAC Gas Source Gen II on Si. The substrate temperature was 750'C. The film was preceded by a low temperature AIN buffer (Tg 425°C). Triethyl gallium (TEGa) and Dimethylethylamine alane (DMEAA) provided the group III fluxes. Reactive nitrogen species were provided by a SVT radio frequency plasma source. Details on the plasma-assisted growth technique have been published previously [14]. A shuttered effusion oven with 4N Er was used for solid source doping. SIMS data on the Er doped GaN film show that Er is located within -0.3 pim of the sample surface. In the spectral PL measurements the 325 nm line of a HeCd laser was employed. The pump beam diameter was -lmm. The lumi
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