Optical and Structural Properties of Er 3+ -Doped GaN Grown by MBE
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Cite this article as: MRS Internet J. Nitride Semicond. Res. 4S1, G3.80(1999)
ABSTRACT We report the morphological and compositional characteristics of Er-doped GaN grown by MBE on Si( 111) substrates and their effect on optical properties. The GaN was grown by molecular beam epitaxy using solid sources (for Ga and Er) and a plasma gas source for N2. The films emit by photoexcitation in the visible and near infrared wavelengths from the Er atomic levels. The morphology of the GaN:Er films was examined by AFM. Composition was determined by SIMS depth profiling that revealed a large Er concentration at 4.5x 102 atoms/cm3 accompanied by a high oxygen impurity concentration. INTRODUCTION Interest in GaN for optoelectronic devices has taken center stage recently since the fabrication of blue lasers by several research groups. These and other optical nitride devices are based on varying Al, In, and Ga composition in heterostructures to achieve wavelength-specific emission. Rare earth (RE) elements are also known to sharply emit light at specific wavelengths independent of the host, which is due to atomic transitions. As a result, devices based on RE materials should be easier to fabricate and require less materials or device design manipulation. Rare earth elements have found wide use in a variety of light-emitting applications, from RE-doped fibers for infrared transmission to upconversion lasers to the phosphors found in CRT
tubes.
In most cases, the RE emits light at wavelengths specific to the atomic transitions
between its 4f energy levels. For years, study of REs incorporated into a semiconductor matrix proceeded because of the possibility that carrier injection from the host could provide the energy necessary to stimulate emission. In addition, semiconductors can be easily integrated into existing electronics. Er is a rare earth well known' for its near-infrared (IR) emission (1.5 pm) which corresponds to the optical fiber loss minimum. Although other Er atomic levels exist, transitions with photonic emission from these states are normally observed only in glass hosts. Typically, the IR transitions seen from RE elements represent the lowest energy transition or GaAs6 78 9 has been the most commonly possible between 4f levels. Er incorporated into Si' studied system, with its characteristic emission only well documented at infrared wavelengths. Recently, we have reported'" '112. the successful in-situ incorporation of Er into GaN by molecular beam epitaxy (MBE) on both sapphire and silicon, which produces room temperature
visible and IR emission by both photoluminescence (PL) and electroluminescence (EL). We also
4 have reported' on Pr-doped GaN grown on Si (11l) substrates and the resulting novel visible red emission at 650 nm by EL and PL, not previously observed outside of glass hosts.
G 3.80 Mat. res. Soc. Syrup. Proc. Vol. 537 0 1999 Materials Research Society
3 Spectroscopically, these specific RE atomic levels in the visible region for Pr" (TP 0) and Er " (2H,,/ 2, 4s /,) are both known to have high
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