Spatial distribution of defects and the kinetics of nonequilibrium charge carriers in GaN wurtzite crystals doped with S
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TRONIC AND OPTICAL PROPERTIES OF SEMICONDUCTORS
Spatial Distribution of Defects and the Kinetics of Nonequilibrium Charge Carriers in GaN Wurtzite Crystals Doped with Sm, Eu, Er, Tm, and Supplementary Zn Impurities M. M. Mezdroginaa^, V. V. Krivolapchuka, and Yu. V. Kozhanovab aIoffe
Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia ^e-mail: [email protected] bSt. Petersburg State Polytechnical University, St. Petersburg, 195251 Russia Submitted May 31, 2007; accepted for publication June 13, 2007
Abstract—By analyzing time-resolved and steady-state photoluminescence spectra, it is established that the spatial distribution of rare-earth ion dopants in wurtzite GaN crystals doped with Sm, Eu, Er, or Tm is governed by the type and concentration of defects in the initial semiconductor matrix as well as by the type of the impurity (its capacity for segregation). Doping with multicharged rare-earth impurities and additionally introduced Zn impurity leads to an intensification of emission. The effect of intensification of emission in the case of n- and p-GaN crystals is considered with the use of the model of isoelectronic traps. PACS numbers: 71.55.Eq, 78.47.+p, 78.55.Cr DOI: 10.1134/S1063782608020073
1. INTRODUCTION Extensive studies of the effect of rare-earth ions (REIs) on the intensity and wavelength of emission from nitrides of III elements have made it possible to conclude that these materials can be used in various fields, specifically, in optoelectronics for the development of displays and in microelectronics for the development of light emitting devices operating as monochromatic emitters in a wide spectral region, from short wavelengths (when doped with Tm) to the near-infrared region (when doped with Eu, Sm, or Er), or as diode emitters of white light. At the same time, there are some unsolved problems in accomplishing intense emission from the wide-gap GaN semiconductor matrix based on f–f intracenter transitions in the REIs, since one is led to meet a number of contradictory requirements in this case. First, it is necessary to provide a maximal concentration of optically active ions, and this should be done without formation of a second phase and without concentrationinduced quenching of the emission; second, the surrounding of the REI should be optimal for energy transfer from the semiconductor matrix to the REI; third, it is necessary to provide occupancy of the f–f levels. Solutions to the above problems have been suggested in a number of studies [1–5]. In particular, among the suggestions have been to use III nitride crystals with the lowest possible concentration of defects, to follow different procedures of introduction of REIs into the semiconductor matrix, to introduce the supplementary Zn or Mg dopants (codopants), to introduce REIs into quantum-confined structures (structures with quantum dots
or quantum wells instead of ordinary p–n junctions), and to subject the system to postgrowth annealing. By now, intense emission (laser effect) typical of the
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