Stimulated Terahertz Stokes Emission of Silicon Crystals Doped with Antimony Donors

Abstract

Stimulated Stokes emission has been observed from silicon crystals doped by antimony donors when optically excited by radiation from a tunable infrared free electron laser. The photon energy of the emission is equal to the pump photon energy reduced by the energy of the intervalley transverse acoustic (TA) g phonon in silicon ( 2:92 THz). The emission frequency covers the range of 4.6 -5.8 THz. The laser process occurs due to a resonant coupling of the 1s E and 1s A 1 donor states (separation 2:97 THz) via the g-TA phonon, which conserves momentum and energy within a single impurity center. DOI: 10.1103/PhysRevLett.96.037404 PACS numbers: 78.47.+p, 41.60.Cr, 42.65.Es, 71.55.Cn In the past few years, significant progress has been made towards silicon based lasers. Silicon is an indirect band gap semiconductor. Therefore, it is difficult to realize an efficient process for light amplification. This fact compels the search for nontraditional approaches for light generation. In the near infrared region, numerous approaches (see Ref.[1] for a review) to overcome this difficulty, such as silicon nanocrystals [2,3], Si=SiO 2 [4] and Si=SiGe [5] superlattices, porous silicon [6], erbium-doped silicon [7], and silicon light-emitting diodes [8], have been attempted. Recently, the first silicon lasers operating at 1:540 and 1:675 m based on stimulated Raman scattering have been reported [9,10]. The Raman effect in silicon occurs via scattering of photons by optical phonons of the crystal. The strongest Stokes emission is due to the threefold degenerate short-wavelength optical modes at the center of the Brillouin zone of silicon [11].The first silicon laser was realized by infrared optical excitation of group-V donor centers embedded in a silicon host lattice [12,13]. For this type of laser, the interaction between phonons and electrons is essential. Except zonecentered optical phonons, intervalley acoustic and optical phonons have been found to play a decisive role in energy and momentum relaxation for nonequilibrium charge carriers in silicon [14,15]. Strong resonant intervalley phononimpurity interaction has been observed in absorption spectra of Bi donors in silicon [16]. When the phonon energy does not exactly coincide with the energy between two impurity states, the contributions from the electronic impurity state and the phonon-related part form a ''mixed'' state, as in silicon doped by Ga [17]. These interactions play an important role in the formation of population inversion between excited states, eventually leading to lasing on particular intracenter transitions in Si:Bi [18] as well as in Si:As [19]. A different situation occurs in silicon doped by antimony (Si:Sb). The energy of the transverse acoustic g-TA intervalley phonon and the energy between the 1s E and 1s A 1 states are almost equal ( 12 and 12.27 meV, respectively). This enhances the nonradiative electronic relaxation between these states. Terahertz intracenter laser emission in Si:Sb has been observed when the crystal was excited by radiation fr...

Isotope effect on the lifetime of the 2p0state in phosphorus-doped silicon

“…These include using shallow donors embedded in a Si matrix as active elements in qubits for quantum computing and spintronics, [6][7][8][9] terahertz lasers operating on donor optical transitions, 10 and terahertz Raman lasers. 11 All of these applications require a detailed understanding of the lifetimes of excited states.…”

The physical principles of terahertz silicon lasers based on intracenter transitions

“…At resonant pumping into one www.pss-b.com of the donor states, such as into the 3p 0 state, the donor emission pulse has the same duration as the pump pulse. But it is shortened in the case of simultaneous generation of donor and Raman lasing, i.e., when pumping into the 2p 0 or 2p AE states [19]. This indicates a competition of these mechanisms, resulting in the suppression of donor lasing on the 2p 0 !…”

“…In these materials the intervalley acoustic g-TA phonon couples the 1s(E) and 1s(T 2 ) states with the 1s(A 1 ) ground state. This dominates the relaxation mechanism and finally makes Si:Sb the most efficient material for Raman lasing [19].…”

“…When both conditions are satisfied, the lowest threshold for the Raman lasing is obtained. In the case of simultaneous donor and Stokes lasing (e.g., pumping into the 2p 0 state) the emission spectra are hardly spectrally resolved without time gating [19,20,85] (see Section 4.5).…”

“…In 2002-2004 several donor silicon lasers utilizing intracenter optical transitions of all group-V donors in silicon were demonstrated [16][17][18]. The first THz Raman-type intracenter silicon laser was reported in 2006 [19]. In the following years this type of Raman laser has been extended to silicon doped with other shallow donors [20][21][22].…”