Eye-safe 2μm luminescence from thulium-doped silicon

Abstract

We report on photoluminescence in the 1:7-2:1 μm range of silicon doped with thulium. This is achieved by the implantation of Tm into silicon that has been codoped with boron to reduce the thermal quenching. At least six strong lines can be distinguished at 80 K; at 300 K, the spectrum is dominated by the main emission at 2 μm. These emissions are attributed to the trivalent Tm 3þ internal transitions between the first excited state and the ground state. © 2011 Optical Society of America OCIS codes: 250.5230, 140.3070, 160.5690, 160.6000. Light emission in the eye-safe 2 μm region is of considerable interest, in particular for medical applications, but also for gas sensing systems and direct free space optical communications. Although 2 μm Tm lasers are now commercially available [1], they are fabricated only in insulating crystals and fiber materials and as a result can be pumped only optically. To achieve electrical pumping, a semiconductor host is required. Because competing radiative transitions across the bandgap are detrimental, indirect rather than direct gap semiconductors are the preferred host, and of these, silicon is by far the most technologically important. In addition, loss mechanisms such as two-photon absorption are reduced by orders of magnitude in indirect rather than direct gap transitions because of the need for the involvement of phonons to conserve momentum. The incorporation of rare-earth (RE) elements into semiconductors, crystals, and glass fibers has been extensively used as optical sources in such materials. The optical transitions that originate from the RE partially filled inner 4f shell are sharp and generally insensitive to the host and temperature variations and can enable light emission throughout the visible to the IR regions. Among the RE elements, thulium is a particularly interesting optical source. The transitions between the three Tm 3þ lower excited states ( 3 H 4 , 3 H 5 , and 3 F 4 ) and the ground state ( 3 H 6 ) can lead to light emission in the 0.8, 1.2, and 2:0 μm regions [2]. Luminescence in the 1:2 μm range has been observed in silicon substrates incorporating Tm, and a Tm:Si-based LED operating at low forward bias has been demonstrated [3,4]. Light emission in the 0:8-2:0 μm range from III-V substrates doped with Tm has also been shown-a summary of previously published work can be found in [3]. A Tm:YAG laser operating at 2 μm was first demonstrated in 1965 [5] and has led to commercial lasers being fabricated in a variety of host crystals and fiber materials [1]. In this Letter, we report on photoluminescence (PL) in the 1:7-2:1 μm region from silicon substrates doped with Tm.Samples were fabricated by ion implantation of 10 13 Tm cm −2 at 400 keV into an n-type Si [100] substrate (2-7 Ω cm) previously implanted with 10 15 B cm −2 at 30 KeV. Subsequently samples were annealed in a nitrogen atmosphere at 850°C for 1, 5, and 15 min. As a reference, Tm was also implanted at the same dose and energy into a Si substrate that did not contain boron and subsequentl...

Role of heavy ion co-implantation and thermal spikes on the development of dislocation loops in nanoengineered silicon light emitting diodes

“…The incorporation of Tm leads to emission of light over two important wavelength regions, 1.2-1.4 lm and 1.7-2.1 lm, which can both support lasing and indeed form the basis of commercially available, optically pumped lasers. In addition, the electrical excitation of the Tm emission has been demonstrated in silicon light emitting diodes under ordinary forward bias 4 and, most recently, 5 room temperature luminescence has been reported at the important, eye-safe, 2 lm wavelength. Significantly, efficient Tm emission in silicon is only achieved in samples coimplanted with B, when dislocation loops are introduced.…”

Silicon‐Modified Rare‐Earth Transitions—A New Route to Near‐ and Mid‐IR Photonics

“…[15][16][17][18][19][20][21] PL and EL from silicon and III-V semiconductors incorporating the RE thulium have also been achieved-transitions between the Tm 3+ lowest excited states and the ground state lead to emissions around 0.8, 1.2, and 2 µm. [22][23][24] Both Er and Tm in silicon, and indeed all others RE reported in silicon Silicon-Modifi ed Rare-Earth Transitions-A New Route to Near-and Mid-IR Photonics Manon A. Lourenço , * Mark A. Hughes , Khue T. Lai , Imran M. Sofi , Willy Ludurczak , Lewis Wong , Russell M. Gwilliam , and Kevin P. Homewood Silicon underpins microelectronics but lacks the photonic capability needed for next-generation systems and currently relies on a highly undesirable hybridization of separate discrete devices using direct band gap semiconductors. Rare-earth (RE) implantation is a promising approach to bestow photonic capability to silicon but is limited to internal RE transition wavelengths.…”

High temperature luminescence of Dy^3+ in crystalline silicon in the optical communication and eye-safe spectral regions

“…The dislocation loops form a barrier for carrier diffusion, thus reducing competing nonradiative recombination. This has led to efficient luminescence [photoluminescence (PL) and electroluminescence] at 1.1 μm from undoped silicon devices [8], at 1.5 μm from Er-doped structures [9], and at 1.3 and 2 μm from Tm-doped [5][6][7] structures.The RE Dy as an emissive optical center has the potential to be utilized in technologically important optoelectronics and medical applications due to its spectral range emission that extends from the UV to the near infrared. …”

“…Luminescence from other RE ions in III-V materials has also been achieved, and an Eu-doped GaN visible laser has been demonstrated [3]. In contrast to III-V materials, light emission from RE-doped crystalline silicon has been restricted to Er [2] and, more recently, Tm [4][5][6][7]. Early reports [2] on the Er:Si system indicated that the solubility of Er in silicon is low, making the incorporation of high concentrations of erbium difficult and leading to very poor luminescence at room temperature.…”

“…The dislocation loops form a barrier for carrier diffusion, thus reducing competing nonradiative recombination. This has led to efficient luminescence [photoluminescence (PL) and electroluminescence] at 1.1 μm from undoped silicon devices [8], at 1.5 μm from Er-doped structures [9], and at 1.3 and 2 μm from Tm-doped [5][6][7] structures.…”