Antifuse injectors for SOI LEDs Giulia Piccolo ,Tu Hoang * , Jisk Holleman, Alexey Y. Kovalgin, Jurriaan Schmitz. MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 7500AE Enschede, The Netherlands e-mail: G.Piccolo@ewi.utwente.nl Abstract - A novel carrier-confinement structure is proposed and realized to generate light in a silicon diode. A significant enhancement of the external power efficiency is observed compared to reference silicon diodes on SOI. I. INTRODUCTION ILICON’s indirect band gap makes an efficient Si LED difficult to make. Yet, such an LED would bring the integration of electronics and photonics a major step further, explaining the significant research interest on the subject [1, 2]. The efficiency of a silicon LED is in practice determined by the ratio between radiative and non-radiative recombination. The radiative recombination rate in silicon is low (as an indirect, phonon-assisted process is necessary). Efforts to improve the efficiency focus on enhancing the radiative recombination through chemical or structural modifications of silicon [3-6], or by confining the carriers [7, 8]. Meanwhile, the nonradiative recombination rate must be kept low, implying high purity silicon (to suppress SRH recombination), good quality Si-SiO surfaces and an injection level below a few times 10 cm (to suppress Auger recombination) [9, 10]. A high concentration of carriers is though needed both to obtain an intense emission and to achieve good ohmic contact in electrically driven devices. The proximity of the contacts (where nonradiative recombination takes place) to the active volume can therefore also play a role in devices without carrier confinement. To overcome this obstacle, one can replace the large junctions between the contacts and the active region (i.e., 3D injectors) with smaller injectors (e.g. 2D and 1D) that confine strongly the carriers in the emitting volume. A tight confinement can result in high concentration of carriers without the need to force large currents through the device, leading to increased power efficiency. As the 2-D injectors have already proved to be beneficial [8], we therefore propose to carry out the next step and investigate the effectiveness of 1-D injectors. 2 17 -3 Our studies focus on a compact, fast-switching silicon LED made with standard CMOS manufacturing techniques and operated at room-temperature. In this work, we investigate the light emission from a small SiO -encapsulated Si volume (around 100 µm ), using antifuses as 1-D injectors for electrons and holes. We report a significant enhancement of the band-to-band radiative recombination as compared to the reference p-i-n SOI-LED with classical 3D injection from junctions, supporting the carrier confinement method. 2 3 II. EXPERIMENTAL Our devices consist of a lowly p-doped central region, electrically isolated by a 10-nm thick thermally grown SiO 2 from an n+ and a p+ polysilicon electrode (see Fig. 1 and Fig. 2a). The electrical isolation is meant to spatially confine electrons and holes in the central region, to increase the probability of their recombination inside this volume (as in [8]). The electrical conduction between the polysilicon electrodes through the mono-Si region was achieved by forcing a breakdown current through the thin dielectrics. Thus, a nanoscopic link, called antifuse, is formed [11], which is then trimmed by forcing a well-defined stress current to obtain the desired conductivity. It appears that the size and resistance of the link-antifuse can be properly adjusted by the programming current. Provided that the programming current is not exceeded, the link is stable and its resistance can hardly be changed by a frequent use of the device. Exceeding the programming current results in a larger link and, therefore, a lower link resistance. The devices were fabricated from a high quality p-type SOI substrate with a resistivity of 14-22 Ω⋅cm. Firstly, the central regions were patterned by dry etching the 300-nm thick SOI layer with a plasma etcher based on Cl 2 chemistry. Secondly, 10 nm of thermal oxide were grown at 900°C in dry oxygen atmosphere. Subsequently, a 340-nm thick LPCVD polysilicon layer was deposited (T=610°C) and then patterned to realize the electrodes. A dose of 5×10 15 cm -2 of P + and B + was implanted to dope the n+ and p+ regions respectively. Dopants were activated by a 30 minutes anneal at 850°C. Metal contact areas were realized by sputtering and patterning Ti/W, as barrier layer, and Al (+1 % Si). A variety of reference n+-p-p+ diodes was fabricated on the same wafer. The reference diodes have standard junctions as injectors, monosilicon p+ and n+ regions instead of polysilicon, and no isolating oxide, The devices were characterized on wafer level both electrically and optically. Their electroluminescence (EL) was measured using a Karl Suss probe station equipped with a spectral XenICs camera with an InGaAs sensor for IR detection. The measurement data were corrected for the losses in the optical system (as in [12]), to obtain the absolute emission. S 573