Mono- and Polycrystalline Silicon for Terahertz Intracenter Lasers

The performance of optically pumped terahertz silicon lasers with active media made from mono- and polycrystalline silicon doped by phosphorus has been investigated. The polycrystalline silicon samples consist of grains with a characteristic size distribution in the range from 50 to 500 µm. Despite of significant changes of the principal phonon spectrum and increased scattering of phonons at grain boundaries, the silicon laser made from polycrystalline material has a laser threshold and an operation temperature only slightly worse than that of monocrystalline silicon lasers

Fast relaxation of free carriers in compensated n- and p-type germanium

The relaxation of free holes and electrons in highly compensated germanium doped by gallium (p-Ge:Ga:Sb) and antimony (n-Ge:Sb:Ga) has been studied by a pump-probe experiment with the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. The relaxation times vary between 20 ps and 300 ps and depend on the incident THz intensity and compensation level. The relaxation times are about five times shorter than previously obtained for uncompensated n-Ge:Sb and p-Ge:Ga. The results support the development of fast photoconductive detectors in the THz frequency range

Multi-crystalline silicon as active medium for terahertz intracenter lasers

Stimulated emission at terahertz frequencies has been obtained from multi-crystalline silicon doped by phosphor under optical excitation by a mid-infrared laser. The silicon samples consist of grains with a characteristic size distribution in the range from 50 to 500 μm. The maximum operation temperature of the laser made from multi-crystalline silicon is 6 K less than that of monocrystalline lasers and the maximum output power is three times less while its laser threshold is only slightly higher and the emission frequency is the same. These effects are attributed to internal strain and enhanced phonon scattering induced by grain boundaries

Terahertz Emission from Phosphor Centers in SiGe and SiGe/Si Semiconductors

Terahertz-range photoluminescence from silicon-germanium crystals and superlattices doped by phosphor has been studied under optical excitation by radiation from a mid-infrared CO2 laser at low temperature. SiGe crystals with a Ge content between 0.9 and 6.5 %, doped by phosphor with a concentration optimal for silicon laser operation, do not exhibit terahertz gain. On the contrary, terahertz-range gain of ~ 2.3 - 3.2 1/cm has been observed for donor-related optical transitions in Si/SiGe strained superlattices at pump intensities above 100 kW/cm2

Towards a life-time-limited 8-octave-infrared photoconductive germanium detector

Ultrafast, ultra-broad-band photoconductive detector based on heavily doped and highly compensated germanium has been demonstrated. Such a material demonstrates optical sensitivity in the more than 8 octaves, in the infrared, from about 2 mm to about 8 μm. The spectral sensitivity peaks up between 2 THz and 2.5 THz and is slowly reduced towards lower and higher frequencies. The life times of free electrons/holes measured by a pump-probe technique approach a few tenths of picoseconds and remain almost independent on the optical input intensity and on the temperature of a detector in the operation range. During operation, a detector is cooled down to liquid helium temperature but has been approved to detect, with a reduced sensitivity, up to liquid nitrogen temperature. The response time is shorter than 200 ps that is significantly faster than previously reported times

Polarization of the induced THz emission of donors in silicon

The polarization of the terahertz (4.9–6.4 THz) stimulated emission of Group-V (Sb, P, As, Bi) donors in single-crystal silicon under pumping (photoionization) by a CO2 laser (photon energy 117 meV), depending on the uniaxial compressive deformation of the crystal along the [100] axis, is experimentally investigated. The influence of the field direction of the pump wave on its efficiency is discussed

Pump-Probe Measurements of Free Carrier Lifetimes in Extrinsic Germanium at FELBE

The capture of free holes and electrons in germanium (Ge) doped by gallium (Ga) or antimony (Sb) as well as is highly doped and compensated germanium has been studied by a time-resolved pump-probe experiment with the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. Results were presented with focus on data evaluation of pump-probe signals

Fast relaxation of free carriers in compensated germanium

We reported on the observation of ultrafast recombination of free electrons and holes in conventionally doped from a melt n-Ge:Sb:Ga and p-Ge:Ga:Sb crystals (net concentration > 2×1015 cm-3) with high level of compensation, up to 50%