1486 JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 26, NO. 11, JUNE 1, 2008 Microwatt MOSLED Using SiO With Buried Si Nanocrystals on Si Nano-Pillar Array Gong-Ru Lin, Senior Member, IEEE, Member, OSA, Yi-Hao Pai, and Cheng-Tao Lin Abstract—Microwatt light emission from a metal–oxide–semi- conductor light-emitting diode (MOSLED) made by using SiO film with buried Si nanocrystals on Si nano-pillar array is demon- strated. The Si nano-pillar array obtained by drying the rapidly self-aggregated Ni nano-dot-masked Si substrate exhibit size, as- pect ratio, and density of 30 nm, 10, and 2.8 cm , re- spectively. These high-aspect-ratio Si nano-pillar array helps to enhance the Fowler–Nordheim tunneling-based carrier injection and to facilitate the complete relaxation on total internal reflec- tion, thus increasing the quantum efficiency by one order of mag- nitude and improving the light extraction from the nano-rough- ened device surface by three times at least. The light-emission in- tensity, turn-on current and power-current slope of the MOSLED are 0.2 mW/cm , 20-30 A, and 3 0.5 mW/A, respectively. At a biased current of 400 A, the highest external quantum efficiency is over 0.2% to obtain the maximum EL power of W. Com- pared with the same device made on smooth Si substrate under a power conversion ratio of 1 10 , such an output power perfor- mance is enhanced by at least one order of magnitude. Index Terms—Metal–oxide–semiconductor light-emitting diode (MOSLED), plasma-enhanced chemical vapor deposition (PECVD), Si nano-pillar array. I. INTRODUCTION P LASMA-enhanced chemical vapor deposition (PECVD)- grown Si-rich SiO or SiO with embedded Si nanocrys- tals (referred hereafter as SiO -Si) of extremely high density have been extensively investigated as a new class of light-emit- ting material over decades [1]–[3]. The SiO -Si-based metal–oxide–semiconductor light-emitting diode (MOSLED) is indeed a potential candidate for next-generation opto- electronic applications such as optical interconnect, optical communication, and microdisplay panels. The advantages of SiO -Si-based MOSLEDs include wavelength-tunable and full-color emission, processing compatibility with other MOS devices, system feasibility, and low cost of fabrication. Electroluminescence (EL) from the SiO -Si film grown by the anomalous PECVD recipe has previously been ob- served [4]–[8]; however, the EL intensity and external quantum efficiency is extremely low due to the nature of indirect re- combination, the insulating property of the host oxide, and Manuscript received Septeber 30, 2007; revised Febuary 26, 2008. This work was supported in part by the National Science Council of Taiwan, R.O.C., and U.S. Air-Force AOARD Office under Grants NSC96–2215-E-002–099 and FA 4869-07-1-4081. The authors are with the Graduate Insistitute of Photonics and Optoelec- tronics, Department of Electrical Engineering, National Taiwan University, Taipei 106, Taiwan, R.O.C. (e-mail: grlin@ntu.edu.tw). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2008.922177 the tunneling dependent carrier injection. Versatile methods were proposed to improve the efficiency of carrier injection into nc-Si, which include the increasing on density of the nc-Si embedded in SiO film, the decreasing thickness of the nc-Si layer, and the bandgap engineering of the contact metal. However, an efficient approach to improve the carrier injection into the nc-Si embedded in the SiO film via the Si nano-roughened surface-based electrode has never been reported. Recently, the fabrication of the Si nano-pillar array based on the electron-beam (E-beam) lithography and induc- tively couple-plasma reactive ion etching (ICP-RIE) process were introduced [9]–[12]. The Si nano-pillar array with its rod size of -nm can be reproduced under the control of E-beam lithography [12]. In addition, the self-assembled metallic nano-dots have also emerged to function as nano-sensor for ei- ther bio-photonics or etching-mask for nano-electronics. Ni has been considered as an alternative to the other noble metals (Au or Ag) for dry-etching the high-aspect-ratio Si nano-pillars on Si substrate [12]–[15]. It is thus worthy discussing the external quantum efficiency for light emission from a SiO -Si-based MOSLED made on such a high-aspect-ratio Si nano-pillar array on Si. In principle, there is an inherent limitation on the quantum efficiency since the light extraction efficiency of most conventional LEDs is limited by the total internal reflection (TIR) of the emitting light from the active region of the LED, which always occurs due to the large difference in the refractive index at the interface between LED top-surface and air. [16] In this letter, we demonstrate a novel SiO -Si MOSLED made on the dense Si nano-pillar array to enhance both the carrier injection and light extraction efficiencies, in which the Si nano-pillars is fabricated by reactive-ion etching an oxide-cov- ered Si substrate encapsulated with the self-assembled Ni nano-dot mask. Anomalous photoluminescence (PL) spectra of Si nano-pillars at visible and near-infrared spectral regions are also investigated. Such a Si nano-pillar array is proposed to enable a microwatt power emitting from the SiO -Si-based MOSLED. The broadband electroluminescent (EL) spectrum and improved turn-on characteristics of such a novel MOSLED, with its external quantum efficiency increasing by enhanced carrier injection and light-extracting mechanisms, are reported. II. SAMPLE PREPARATION To fabricate a SiO -based MOSLED on Si nano-pillar array, the Si nano-pillar roughened Si substrate surface is obtained by rapid thermal annealing a 5-nm-thick Ni film evaporated on a 20-nm-thick SiO layer covered Si substrate to induce self-ag- gregation of a two-dimensional randomized Ni nano-dots mask [17]. Subsequently, a large-area Si nano-pillar array with rod 0733-8724/$25.00 © 2008 IEEE Authorized licensed use limited to: National Taiwan University. Downloaded on February 10, 2009 at 22:57 from IEEE Xplore. Restrictions apply.