Stress-controlled phonon-impurity resonances in terahertz silicon lasers
- PDF / 1,028,211 Bytes
- 11 Pages / 612 x 792 pts (letter) Page_size
- 10 Downloads / 228 Views
1221-CC09-02
Stress-controlled phonon-impurity resonances in terahertz silicon lasers Sergey G. Pavlov Institute of Planetary Research, German Aerospace Center, 2 Rutherfordstr., Berlin, 12489, Germany ABSTRACT Optically pumped terahertz silicon lasers utilize transitions between shallow donor states at low lattice temperatures. Population inversion in these lasers is built-up due to selective relaxation routes of optically excited electrons into impurity ground state. Each relaxation step of the electron occurs under assistance of intervalley and intravalley phonons with energies approaching the particular energy gaps between interacting excited donor states. These impurity phonon interactions determine, at the end, the lifetimes of the laser levels, and, therefore, efficiency of intracenter silicon lasers. Deformation of silicon crystal is a classical example of controllable influence on energy spectrum of shallow donor levels due to specific splitting and shifts of conduction band valleys. Using moderate (up to 400MPa) external uniaxial deformation of a crystal, one can radically modify the impurity spectra while the phononic spectra remain almost unchanged. We have demonstrated significant improvement of efficiency for intracenter silicon lasers followed by changes of lifetime for the upper and the lower laser levels due to moving the impurity levels either into or out of resonance with corresponding intervalley phonon frequencies. INTRODUCTION Terahertz-range intracenter silicon lasers operate on optical transitions between particular states of the group-V donor centers (see, for a review [1]) under optical excitation and low lattice temperatures. Together with the Raman-type near-infrared [2,3] and far-infrared [4,5] silicon lasers, they represent the successful demonstration of stimulated light emission under optical excitation of silicon. All these lasers use interaction with high-energy principal phonons of a host lattice to build up the stimulated emission. The characteristic feature of such interactions is its very short time and certain probability, which makes electron-phonon interaction dominating in most of processes forming strongly non-equilibrium populations of electronic, photonic and phononic distributions in silicon. An alternative to optical pumping electrical excitation approach is preferably seen for development of silicon-based photonic devices. Several approaches to realize electrically excited lasers have been studied. Electrically-induced luminescence from electrically excited silicon doped by shallow impurities [6,7], from silicon nanocrystals [8], and from silicon-based heterostructures [9] as well as from erbium doped silicon [10,11] has been thoroughly studied over past years. The population inversion in terahertz silicon lasers is formed entirely as a result of capture and relaxation of photoionized electrons through excited donor states towards ground donor state. The rates of these processes are fully determined by electron-phonon interaction. For donor states with a large interst
Data Loading...
