A far-infrared laser concept based on intersubband transitions of holes in p-type periodically delta-doped semiconductor films is studied using numerical Monte Carlo simulation of hot-hole dynamics. The considered device consists of monocrystalline pure Ge layers periodically interleaved with delta-doped layers and operates with vertical hole transport in the presence of an in-plane magnetic field. Population inversion on intersubband transitions arises due to light-hole accumulation in E Ќ B fields, as in the bulk p-Ge laser. However, the considered structure achieves spatial separation of hole accumulation regions from the doped layers, which reduces ionized-impurity and carrier-carrier scattering for the majority of light holes. This allows a remarkable increase of the gain in comparison with bulk p-Ge lasers. Population inversion and gain sufficient for laser operation are expected up to 77 K. Test structures grown by chemical-vapor deposition demonstrate feasibility of producing the device with sufficient active thickness to allow quasioptical electrodynamic cavity solutions.

Transitions between valence subbands resulting from hole-hole scattering in cubic semiconductors have been analyzed in the frame of Coulomb interaction of valence electrons in the Luttinger-Kohn representation. Expressions for transition rates are derived. Calculated rates for transitions between light-and heavy-hole bands are presented for germanium. Hole-hole scattering has remarkably different transition probabilities and scattering-angle dependence than for scattering of holes on ionized impurities. These results are particularly important for hole lifetimes and relative subband populations in unipolar p-type devices, such as the hot hole p-Ge laser. Features of hole-hole scattering for spin polarized hole distributions are also discussed.

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY) SPONSOR/MONITOR'S ACRONYM(S) AFRL-RY-HS SPONSOR/MONITOR'S REPORT NUMBER(S) AFRL-RY-HS-TP-2008-0020 DISTRIBUTION / AVAILABILITY STATEMENTDISTRIBUTION A: APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED. SUPPLEMENTARY NOTESThe U. S. Government is joint author of this work and has the right to use, modify, reproduce, release, perform, display, or disclose the work. Published in Proc. of SPIE, Vol 6212 (2006). Cleared for Public Release by ESC/PA number: ESC-06-0670. ABSTRACTA concept for a terahertz laser in vapor-phase-grown homoepitaxial GaAs with spatially periodic doping profile was theoretically explored. Monte Carlo simulation of hole transport in multilayer delta-doped p-GaAs/GaAs structures in crossed electric and magnetic fields was performed to investigate possibilities of the terahertz amplification on intervalence-band light-to-heavy hole transitions. The results are compared to those calculated for uniformly doped bulk p-GaAs and recently proposed p-Ge/Ge structures. The improvement in the gain for delta-doped p-GaAs structures is about ~ 2 -3 times over bulk p-GaAs. Terahertz laser generation in the considered GaAs device concept appears feasible, as is growth of structures with active thicknesses sufficient to support quasioptical cavity solutions at 100 m vacuum wavelengths. Potential applications for the considered laser device include sensing of chem/bio agents and explosives, biomedical imaging, non-destructive testing, and communications. . SUBJECT TERMSterahertz, far infrared, laser, germanium, silicon, gallium arsenide, epitaxy. ABSTRACT A concept for a terahertz laser in vapor-phase-grown homoepitaxial GaAs with spatially periodic doping profile was theoretically explored. Monte Carlo simulation of hole transport in multilayer delta-doped p-GaAs/GaAs structures in crossed electric and magnetic fields was performed to investigate possibilities of the terahertz amplification on intervalence-band light-to-heavy hole transitions. The results are compared to those calculated for uniformly doped bulk pGaAs and recently proposed p-Ge/Ge structures. The improvement in the ga...

Amplification of terahertz radiation on intersubband transitions has been analyzed by numerical Monte Carlo simulation for p-type delta-doped Ge films with in-plane transport configuration of applied electric and magnetic fields. A significant increase of the gain is found, compared to existing bulk p-Ge lasers, due to spatial separation of light and heavy hole streams, which reduces scattering of light holes on ionized impurities and heavy holes. The considered device has potential as a widely tunable (2–4THz) laser with high duty cycle and operating temperatures up to 50K.

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A far-infrared p-type germanium laser with active crystal prepared from ultra pure single-crystal Ge by neutron transmutation doping ͑NTD͒ is demonstrated. Calculations show that the high uniformity of Ga acceptor distribution achieved by NTD significantly improves average gain. The stronger ionized impurity scattering due to high compensation in NTD Ge is shown to have insignificant negative impact on the gain at the moderate doping concentrations sufficient for laser operation. Experimentally, this first NTD laser is found to have lower current-density lasing threshold than the best of a number of melt-doped laser crystals studied for comparison.

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The formula for the nonpolar optical phonon scattering rate of holes in cubic semiconductors is obtained in the case of strong valence band anisotropy. The deformation potential approximation is used. A three-band, 6×6, k∙p Luttinger-Kohn representation includes states belonging to the heavy, light, and split-off bands. Mixing with the latter causes strong anisotropy in the transition matrix elements as well as in the density of final states. The derived formula is recommended for silicon, where inter- and intravalence-band scattering rates are much more strongly anisotropic and have significantly different values than those estimated from the usual two-band 4×4, “warped spheres” approximation that neglects the split-off band. Results for the more isotropic case of germanium are presented for comparison.