Origin of anomalous temperature dependence and high efficiency of silicon light-emitting diodes

Abstract

Efficient electroluminescence with power efficiency up to 0.12% is observed from silicon pn diodes prepared by boron implantation with boron concentrations above the solubility limit at the postimplantation annealing temperature. The electroluminescence spectra exhibit a transition from two bound-exciton bands towards the free electron-hole pair recombination with an anomalous increase in the total intensity with increasing temperature. The implantation dose and temperature dependences of the relative peak intensities provide evidence for the relevance of excitonic traps as a supply for free electron-hole pairs and thus for the origin of the enhanced electroluminescence at elevated temperatures. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1626809͔The implementation of silicon-based optoelectronics requires the realization of light emitters, waveguides, and photodiodes compatible with standard silicon processing technology. 1 Light emitters, such as silicon nanoclusters, Erdoped Si-rich SiO 2 , SiGe quantum dots, and silicon pn junctions are presently considered as potential light sources. 2 The latter ones are especially attractive, since they are fully compatible with silicon ultralarge-scale integration technology including low operation voltages. Although bulk silicon, being an indirect semiconductor with inefficient radiative recombination, has been neglected for this purpose for a long time, significant improvements in the electroluminescence ͑EL͒ efficiency from bulk silicon pn diodes have been reported recently. 3,4 The main concept for improving the light emission from silicon is based on a decrease of nonradiative decay channels possibly with carrier confinement in the active region of the device. Green et al. 3 employed surface texturing in combination with efficient surface passivation of high-purity float-zone silicon to improve the light extraction from the pn junction. Ng et al. 4 prepared silicon lightemitting diodes by high boron-dose implantation for the p-type doping in silicon pn junctions. They explained the increased EL efficiency by carrier confinement introduced by dislocation loops formed during implantation, where the strain-induced potential at dislocations loops prevents carriers from diffusing to nonradiative channels, thus leading to a strong band edge electron-hole recombination. Similar high EL efficiency was also reported in silicon p ϩ n junctions prepared by thermal diffusion of high boron concentrations (3 ϫ10 19 cm Ϫ3 ) in the surface layer. 5 All these pn diodes with highly boron-doped surface layers have in common the interesting feature of an anomalous increase in EL efficiency with temperature, which is in stark contrast to the conventional behavior of photoluminescence from bulk silicon. A study of this anomalous temperature dependence is essential for the understanding of the enhancement of the EL with increased boron doses. However, up to now no detailed experimental investigation has been reported for clarifying the origin of the anomalous temperature depende...

Below-band-gap electroluminescence related to doping spikes in boron-implanted siliconpndiodes

“…In this paper, we present a detailed study on the origin of the two luminescence peaks observed at low lattice temperatures from bound excitons in silicon, which are relevant for the efficient EL from silicon pn diodes produced by ion implantation. 10 A close relationship between the boundexciton luminescence and the formation of locally enhanced boron doping spikes is observed. This relationship is supported by results of cross-sectional transmission electron microscopy (XTEM), by introducing excess defects with Si + implantation, as well as by changing the boron doses and annealing times.…”

“…The doping spikes significantly contribute to the efficient EL from band edge recombination via the release of free electron-hole pairs at elevated temperatures, thus playing an important role for the efficiency of the diodes at room temperature as observed in our previous work. 10 This paper is organized as follows: In Sec. II we summarize the fabrication steps of the pn diodes and the experimental methods applied.…”

Bright green electroluminescence from Tb3+ in silicon metal-oxide-semiconductor devices

“…4 Recently, several approaches for gaining light from silicon-based systems have been reported with the prospect of sufficient electroluminescence ͑EL͒ efficiency. The most prominent systems are porous silicon, 5 silicon nanocrystals in SiO 2 , 6 p-n diodes, 7,8 Ge + -implanted SiO 2 , 9 and Er-doped silicon-rich SiO 2 sensitized with silicon nanocrystals. 10,11 The latter ones, realized as metal-oxide-semiconductor ͑MOS͒ light emitters, are especially attractive, since they are fully compatible with silicon complementary metal-oxidesemiconductor ͑CMOS͒ technology.…”

Silicon-on-insulator microcavity light emitting diodes with two Si/SiO2 Bragg reflectors

“…In more recent attempts, photonic-crystal structures were integrated into Si based LEDs [5][6][7]. Here we use highly boron doped Si pn junction LEDs, which have been shown to show room-temperature EL at a wavelength of 1150 nm with a reasonably high power efficiency of 40.1% [8,9]. In continuation of our work using a buried CoSi 2 mirror [10], we present here the design and fabrication of a RCLED with two distributed Bragg reflectors (DBR).…”