Lionel R. Friedman

Intersubband lasing lifetimes of SiGe/Si and GaAs/ AlGaAs multiple quantum well structures

The feasibility of population inversion is studied for the SiGe/Si system and compared with that of GaAs/AlGaAs. Because of the absence of strong polar optical phonon scattering in SiGe/Si, the lifetime difference of the upper and lower lasing levels, to which the population inversion and laser gain are proportional, is consistently an order of magnitude larger than that of GaAs/AlGaAs; nor does it show the sudden drop to zero or negative values when the lasing energy exceeds the optical phonon energy. Both systems studied are superlattices, each period of which consists of three coupled quantum wells and barriers.

Comparative analysis of optically pumped intersubband lasers and intersubband Raman oscillators

A new tunable source of the far‐infrared radiation based on intersubband electronic Raman scattering in semiconductor quantum wells is proposed. The gain and threshold of the proposed Raman oscillator are estimated and compared with the intersubband laser.

Progress toward silicon-based intersubband lasers

Design results are presented for the quantum parallel laser (QPL) at 1–20 μm wavelengths and the cryogenic 4–20 μm quantum cascade laser (QCL). For 1–2 μm lasing, the optimum multiple quantum well heterostructures are Si quantum wells (QWs) confined by wide-gap lattice-matched semiconductor layers, especially the Si/ZnS, Si/BeSeTe, Si/γ–Al2O3, Si/CeO2, and Si/SiOx systems (SiOx is a crystalline suboxide). The electrically pumped 300 K unipolar p-i-p. QPL consists of tightly coupled QWs exhibiting coherent transport of carriers on superlattice (SL) minibands. A good QPL candidate is the symmetrically strained Gen–Sin SL grown on relaxed Si0.5Ge0.5. Local-in-k population inversion is engineered between two valence minibands. Our calculations indicate that the p-i-p QCL is feasible in Ge–Si or in lattice-matched Si0.63Ge0.33C0.04/Si. The oscillator strength fz=0.1 calculated for the 8 ML×8 ML Si/ZnS zone-folded SL is insufficient for 1.1 μm band-to-band lasing; however, the in-plane dispersion of Si QWs in S...

Intersubband lasing in silicon-based multiple quantum wells

Because of the absence of polar optical scattering, the lifetime difference of the upper and lower lasing levels, to which population inversion and laser gain are proportional, is an order of magnitude larger in silicon-based structures than in the III-Vs. Further enhancements are due to phonon confinement. For lasing wavelengths 10 micrometers and longer, GexSi1-x/Si is used. For operation at near infrared wavelengths, high barrier materials are needed. To avoid large operating voltages, designs are considered which rely on parallel rather than sequential operation.

Optically pumped intersubband electron Raman lasers

A new tunable source of infrared radiation based on intersubband electron Raman scattering in semiconductor quantum wells is theoretically studied. The structure consisting of three levels in two coupled GaAs/AlGaAs quantum wells is optimized for a maximum Raman gain at zero bias. Raman gain as large as 400/cm can be achieved according to our calculations. Lasing wavelengths are tuned by applying external dc bias field along the growth direction. An infrared tuning range of 8 to 12 micrometers , with moderate Raman gain, is predicted as the electric field is varied from -40 to 40 kV/cm.

Electro-optical modulation in silicon-silicon/germanium quantum-well structures

A new, fast, intersubband 1.55 micrometers electro-optic modulator in the SiGe/Si/CaF2-on- Si stepped-quantum-well system is proposed and analyzed. At applied electric fields of +/- 8 V/micrometers , resonant 1 - 3 conduction-intersubband absorption is predicted to given 18 dB of optical extinction for narrow-linewidth transitions. The procedure for incorporating conduction band nonparobolicity for higher lying subbands is described, and the issue of narrow linewidths is discussed.