1556 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 12, NO. 6, NOVEMBER/DECEMBER 2006 Effect of Space Charge Region Width on Er-Related Luminescence in Reverse Biased Si:Er-Based Light Emitting Diodes Viacheslav B. Shmagin, Sergey V. Obolensky, Dmitry Yu. Remizov, Viktor P. Kuznetsov, and Zakhary F. Krasilnik Abstract—In this paper, an effect of space charge region (SCR) width on Er-related electroluminescence (EL) in reverse biased Si:Er-based light-emitting diodes (LEDs) is under investigation. It is concluded that a trivial widening of the SCR in the examined LEDs with triangular and trapezoidal electric field profiles through SCR does not result in a desirable increase in the Er-related EL intensity. The tunnel transit-time diode structure with a compli- cated electric field profile through SCR is offered to increase the Er-related EL intensity. The difficulties hampering this process in erbium EL from reverse biased LEDs are under discussion. Index Terms—Erbium-doped silicon, impact excitation, light emitting diodes, p-n junction breakdown. I. INTRODUCTION D OPING silicon with rare earth elements including erbium has been considered, so far, as an opportunity to overcome the limitation due to the indirect band gap of silicon and thus to promote wide use of silicon in optoelectronic applications. Erbium when introduced into a silicon matrix is characterized, in its 3+ state, by a radiative intra-4f shell transition 4 I 13/2 → 4 I 15/2 emitting at a wavelength of 1.54 μm (0.81 eV) which falls into the window of maximum transmission for the silica optical fibers. It is rather an attractive feature of Si:Er emitters. The next feature, not of any lesser importance, is the high Er 3+ excitation cross section stimulated by carrier-mediated processes (up to 3 × 10 −15 cm 2 under the excitation of Er 3+ via electron–hole recombination on an Er-related deep defect [1]) as opposed to the direct optical excitation of Er 3+ in dielectric matrixes (1 × 10 −20 cm 2 in SiO 2 [2]). An impact excitation of erbium ions with hot carriers real- ized in reverse biased p–n junctions was found the most ef- fective at room temperature [3]. Its advantages are connected with both the high excitation cross section (up to 2 × 10 −16 cm 2 at room temperature [4]) and the strong suppression of non- radiative Er 3+ relaxation processes in the space charge region Manuscript received October 31, 2005; revised August 28, 2006. This work was supported in part by the Russian Foundation for Basic Research under Grant 04-02-17120 and Grant 06-02-16563. V. B. Shmagin and D. Yu. Remizov are with the Institute for Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod 603950, Russia (e-mail: shm@ipm.sci-nnov.ru; remizov@ipm.sci-nnov.ru). S. V. Obolensky and V. P. Kuznetsov are with Nizhny Novgorod State Uni- versity, Nizhny Novgorod 603950, Russia (e-mail: obolensk@rf.unn.ru). Z. F. Krasilnik is with the Institute for Physics of Microstructures Russian Academy of Sciences, Nizhny Novgorod 603950, Russia, and also with Nizhny Novgorod State University, Nizhny Novgorod 603950, Russia (e-mail: zfk@ipm.sci-nnov.ru). Digital Object Identifier 10.1109/JSTQE.2006.884066 (SCR) of a reverse biased p–n junction: Auger with free carriers and back-transfer processes. Its principal shortcoming results from a small SCR width at the used dopants concentration. The SCR width determines practically the surface density of Er 3+ ions per unit of p–n junction area and influences strongly the electroluminescence (EL) intensity. Recently, the potential of an original sublimation molecular beam epitaxy (SMBE) technique in growing Si:Er based struc- tures have been demonstrated successfully by revealing the na- ture of light-emitting centers in SMBE grown Si:Er layers [5], by the development of light-emitting devices efficiently radiat- ing at 1.54 μm [6], and the observation of population inversion of the Er 3+ energy levels in Si/Si 1−x Ge x :Er/Si structures [7]. In this paper, we study the effect produced by SCR widening on the EL intensity from SMBE grown light-emitting diodes (LEDs) with different dopants and electric field distributions through SCR and discuss the possibilities to increase the Er-related EL intensity from reverse biased Si:Er based p–n junctions. II. EXPERIMENTAL The LEDs considered in this paper were grown accord- ing to an original SMBE technique, which is a modifica- tion of the standard MBE, where fluxes of Si and required dopants are produced by sublimation of a Si crystal intention- ally doped with these impurities [8]. All of the samples were grown on p-Si(1 0 0) substrates with the specific resistivity of 10–20 Ω·cm. The Er and O concentrations in Si:Er lay- ers were about (3–5) × 10 18 and (1–10) × 10 19 cm −3 respec- tively, the free-carrier concentration varied from 1 × 10 16 to 1 × 10 18 cm −3 , the layer thickness ranged from 0.01 to 1.2 μm. The growth temperature was 520 ◦ C–580 ◦ C. Mesa-like diode structures were fabricated using the conventional mesa technol- ogy; the mesa’s area was ∼ 2.5 mm 2 , with 70% of this area being transparent to the generated light. The used SMBE technique allowed growing epilayers with the thickness and the carrier concentration continuously varying along the substrate length. It eventually made it possible to produce a series of LEDs with smoothly varying parameters in a single growth cycle, which was essential in engineering the new LEDs. SMBE allowed individual variations of the erbium and donor concentrations in Si:Er layers, which made it easier to control the p–n junction breakdown mechanism. EL spectra obtained using excitation with a pulse drive cur- rent (the pulse duration was 4 ms, the frequency was 40 Hz, the current was up to 500 mA), taken in the range of 1.0–1.6 μm us- ing a single grating monochromator, an InGaAs detector (with 1077-260X/$20.00 © 2006 IEEE