Efficient Point Defect Engineered Si Light-emitting Diode at 1.218 µm Jiming Bao 1 , Malek Tabbal 1* , Taegon Kim 1 , Supakit Charnvanichborikarn 2 , James S. Williams 2 , Michael. J. Aziz 1 and Federico Capasso 1 1 Division of Engineering and Applied Sciences, Harvard University Cambridge, MA, 02138 2 Research School of Physical Sciences and Engineering, Australian National University, Canberra, Australia, 0200 *Department of Physics, American University of Beirut, Riad El Solh, Beirut, 1107 2020, Lebanon jmbao@deas.harvard.edu, capasso@deas.harvard.edu Abstract: We have demonstrated a Si LED with an internal quantum efficiency ~ 10 % using a novel approach to enhance light emission based on point defect engineering, which uses state-of- the art technology. ©2007 Optical Society of America OCIS Codes: 230.3670 Light-emitting diodes; 160.6000 Semiconductors. The inset of Fig. 1 shows a schematic cross section of the light-emitting diode (LED). The LED consists of an optically active region, an n + top layer and a p-type substrate. It was fabricated on a Si(001) p-type (5 Ωcm) wafer, which was ion implanted at 77 K with 80 keV 28 Si + to a dose of 10 15 /cm 2 and subsequently with 80 keV 34 S + to a dose of 10 14 /cm 2 . Samples were subsequently irradiated by a single 1.4 J/cm 2 pulse from a spatially homogenized pulsed XeCl + excimer laser (308 nm wavelength, 25 ns full width at half maximum, 50 ns total pulse duration). A 2.8 µm deep, 120 µm × 3 mm ridge structure was then defined on the wafer by photolithography, reactive ion etching (RIE) and mechanical cleaving. The metallic contacts (back contact Al, 1500 nm; front contact Ti, 5 nm followed by Au, 100 nm) were fabricated using electron-beam evaporation. Finally, the device was processed with rapid thermal annealing (RTA) for two minutes at 275 o C. The ion implantation, together with pulsed laser melting (PLM) not only induce a n + top layer[1], but also create a Si-interstitial rich layer which is a ~1 µm thick region lying immediately beneath the implantation-doped region[2,3]. This interstitial-rich region defines the active region of our device where electroluminescence at wavelength λ = 1.218 µm is generated[4]. Photoluminescence (PL) and electroluminescence (EL) measurements were performed in a continuous flow optical cryostat at various temperatures. The 458 nm line from an argon ion laser was used to optically excite samples, and luminescence was collected and analyzed by a single grating spectrometer equipped with an InGaAs infrared detector. Fig. 1 shows a typical surface-emission PL spectrum of a sample. The sample was prepared as other LED samples, except that it had no metallic contacts. The PL spectrum shows a strong W-line at 1.218 µm, as well as other weaker lines at longer wavelength[2-4]. These long wavelength weak lines are phonon replicas of the W-line. Current (I) vs. voltage (V) characteristics at 6 K is shown in the inset of Fig. 2. The I-V curves show a very good rectifying behavior. The increase of turn-on voltage at low temperature is attributed to the high resistance of the p- type substrate due to carrier freeze out effects. Electroluminescence is obtained from a cleaved edge of the device. Spectrum at 6 K is shown in Fig. 2. Similar to the PL spectrum at low temperature, a strong W-line is about three orders of magnitude stronger than that of band-edge emission. The high intensity of the W-line emission compared to Si band-edge emission at low temperature indicates two important properties of the device. First, W-line defects have an efficient electronic transition, in contrast to the forbidden transition near the Si bandgap. Second, the injected electrons and holes are efficiently captured and then recombine near the defect-rich active region. Because the band-edge luminescence of silicon has an internal quantum efficiency of ~10 -4 [5], the internal quantum efficiency of our W-line LED is estimated to be ~10%. This estimate assumes that the wavelengths are so close that the optics are similar, and that the presence of W-line defects does not change the band-edge luminescence. a929_1.pdf JTuA95.pdf