Silicon light-emitting diodes with strong near-band-edge luminescence
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Silicon Light-Emitting Diodes with Strong Near-Band-Edge Luminescence A. M. Emel’yanov^ and N. A. Sobolev^^ Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia ^e-mail: [email protected] ^^e-mail: [email protected] Submitted May 17, 2007; accepted for publication May 28, 2007
Abstract—Electroluminescence (EL) in the region of interband transitions from silicon light-emitting diodes (LEDs) fabricated by cutting a solar cell with an area of 21 cm2 and external quantum efficiency ηext of EL up to 0.85% has been studied at room temperature. Despite the considerable decrease in ηext because of the cutting and Auger recombination, record-breaking values of the total power emitted by a diode (up to W = 8 mW) and emitted power per unit area (up to P0 = 65 mW/cm2) were achieved at pulse currents of up to 10 A and structure areas in the range S = 0.1–0.9 cm2. The EL decay kinetics was measured for LEDs with different areas. The emission pattern of a Si LED with a textured surface and the emission intensity distribution along different directions in the plane of the emitting area of the LED were measured. PACS numbers: 78.60.Fi, 78.60.-b, 78.55.Ap DOI: 10.1134/S1063782608030160
1. INTRODUCTION Single-crystal silicon (c-Si) is a nondirect-gap semiconductor and, therefore, has been regarded as an inefficient source of luminescence until recently, when it was shown [1–3] that the external quantum efficiency (ηext) of luminescence in the region of interband transitions in cSi at room temperature may be comparable with ηext of light-emitting structures based on direct-gap semiconductors. For example, the following values were obtained at room temperature: ηext ≈ 1% for electroluminescence (EL) [1] and ηext ≈ 6% for photoluminescence (PL) in c-Si [2]. These high (for nondirect-gap semiconductors) values of ηext were provided by the use of high-quality c-Si wafers with large minority carrier lifetimes, preservation of these large values in finished devices, passivation of the silicon surface, and a special diode design aimed to minimize the interfacial recombination. In addition, surface texturing was used to raise significantly (approximately by an order of magnitude) the ratio between the external and internal quantum efficiencies. It was suggested in the literature that high-efficiency (ηext ≈ 0.1%) Si light-emitting diodes (LEDs) can be formed by ion implantation of boron into n-Si and subsequent annealing at 1000°C [3]. The dislocation loops introduced in this case form, as assumed by the authors of [3], a spatial confinement for minority carriers, which precludes their nonradiative recombination and thereby substantially raises the quantum efficiency of the interband EL. However, later studies of the effect of
the postimplantation annealing temperature on the quantum efficiency and on the spectrum of extended structural defects have shown [4–6] that the model suggested in [3] is incorrect. Thus, only the technology described in [1] enables rep
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