Competing Inversion-Based Lasing and Raman Lasing in Doped Silicon

We report on an optically pumped laser where photons are simultaneously generated by population inversion and by stimulated Raman scattering in the same active medium, namely crystalline silicon doped by bismuth (SiBi). The medium utilizes three electronic levels: ground state [|

Cascade capture of charge carriers in highly doped semiconductors

We analyze the cascade capture of charge carriers due to the interaction with acoustic phonons in highly doped semiconductors using a model that describes the recombination of photo-ionized carriers as a continuous relaxation of carriers in the energy space at both positive and negative energies in the field of a set of impurity ions. Such description enables simultaneous calculation of non-equilibrium carrier distribution formed by interaction with acoustic phonons in the presence of impurity traps, and the time of recombination in a wide range of concentrations of capture centers and phonon temperatures. Additionally, we calculated the time of cascade recombination in the presence of fast scattering processes forming a Maxwellian distribution of free carriers. We show that experimentally observed concentration and temperature dependence of carrier life times in highly doped semiconductors can be described within the model of the cascade capture to uniformly spaced capture centers, and the main factor that determines the regime of cascade capture is the ratio of the thermal energy and the energy of the overlap of impurity potentials

Time-resolved electronic capture in germanium doped with hydrogen-like impurity centers

The capture of free holes and electrons in germanium (Ge) doped by gallium (Ga) or antimony (Sb) has been studied by a time-resolved pump-probe experiment with the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. For Ga acceptors the relaxation times decrease with increasing pump power from approximately 3 ns to 1 ns (2 ns and 1 ns for Sb donors, respectively). The results support the development of fast photoconductive detectors in the terahertz frequency range

Time-resolved electronic capture in germanium doped with hydrogen-like impurity centers

The capture of free holes and electrons in germanium (Ge) doped by gallium (Ga) or antimony (Sb) has been studied by a time-resolved pump-probe experiment with the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. For Ga acceptors the relaxation times decrease with increasing pump power from approximately 3 ns to 1 ns (2 ns and 1 ns for Sb donors, respectively). The results support the development of fast photoconductive detectors in the terahertz frequency range

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

Stimulated Raman emission in the far-infrared range from doped silicon enabled by FELIX

Stimulated Raman emission has been realized in the range 47-67μm from natural and isotopically enriched crystals with various dopants when the FELIX wavelength was between 19 and 41 μm. Typical Raman lasing thresholds are from 10^24 photon/cm2/s. The observed Stokes shifts of the stimulated emission enable the determination of transition energies of even-parity excited donor states that are not accessible by conventional infrared absorption spectroscopy

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

Photoassisted ionization spectroscopy of few implanted bismuth orbitals in a silicon-on-insulator device

The electrically detected orbital spectrum of a mesoscopic silicon device containing a small number of donors has been investigated. The device was fabricated on silicon-on-insulator with an optically active channel containing 6 x 105 substitutional bismuth centers introduced by ion implantation. The 1s(A₁) → 2p± orbital transition at the energy associated with isolated bismuth donors was detected via a change in photocurrent when illuminated by THz light from a free electron laser. The spectral dependence on bias, temperature, and laser intensity is explored to determine optimum conditions for detecting orbital transitions in smaller devices with fewer donors. These results suggest that photo-induced impact ionization can offer a route for the spectroscopic detection of few impurities providing a useful tool for the development of solid-state quantum technologies

Extremely fast electron capture in moderately doped germanium

We report the observation of ultrafast capture of free electrons (n-Ge:Sb:Ga) and holes (p-Ge:Ga:Sb) in moderately doped (net concentration > 2×10^15/cm3) Ge with high compensation, up to 50%. The typical range of the relaxation times for photoinduced (far-infrared photo- ionization) transmittance is in the range of 20-300 ps dependent on the sample characteristics and the far-infrared light intensity. Measurements of the photoinduced decay have been carried out by a contactless pump-probe technique at the infrared free electron laser facility at HZDR, Dresden. The observed relaxation times of free charge carriers are up to two orders of magnitude shorter than the ~ 2 ns response time observed in the photoconductive response of neutron transmutation doped isotope-fixed compensated p-Ge:Ga:Se:As. This indicates the potential for very fast broad band detection of infrared pulses by extrinsic photoconductive germanium detectors with optimized doping, compensation, geometry and an appropriate electrical readout circuit