Far-infrared semiconductor lasers

Gornik, E.; Andronov, A. A.

doi:10.1007/bf00619760

“…One need only sum over one set of polarizations. We obtain 24) where n is the index of refraction at the frequency ω 0 = (E i − E f )/h, and c is the speed of light in a vacuum. As shown above, the spontaneous emission rate can be expressed in terms of the dipole matrix element, or the scaled oscillator strength …”

Section: Spontaneous Emission Lifetimementioning

confidence: 99%

Terahertz quantum-cascade lasers

Williams

¹

2007

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The development of the terahertz frequency range (1-10 THz, λ ≈ 30-300 µm) has long been impeded by the relative dearth of compact, coherent radiation sources of reasonable power. This thesis details the development of quantum cascade lasers (QCLs) that operate in the terahertz with photon energies below the semiconductor Reststrahlen band. Photons are emitted via electronic intersubband transitions that take place entirely within the conduction band, where the wavelength is chosen by engineering the well and barrier widths in multiple-quantum-well heterostructures. Fabrication of such long wavelength lasers has traditionally been challenging, since it is difficult to obtain a population inversion between such closely spaced energy levels (hω ≈ 4-40 meV), and because traditional dielectric waveguides become extremely lossy due to free carrier absorption.This thesis reports the development of terahertz QCLs in which the lower radiative state is depopulated via resonant longitudinal-optical phonon scattering. This mechanism is efficient and temperature insensitive, and provides protection from thermal backfilling due to the large energy separation (∼36 meV) between the lower radiative state and the injector. Both properties are important in allowing higher temperature operation at longer wavelengths. Lasers using a surface plasmon based waveguide grown on a semi-insulating (SI) GaAs substrate were demonstrated at 3.4 THz (λ ≈ 88 µm) in pulsed mode up to 87 K, with peak collected powers of 14 mW at 5 K, and 4 mW at 77 K.Additionally, the first terahertz QCLs have been demonstrated that use metalmetal waveguides, where the mode is confined between metal layers placed immediately above and below the active region. These devices have confinement factors close to unity, and are expected to be advantageous over SI-surface-plasmon waveguides, especially at long wavelengths. Such a waveguide was used to obtain lasing at 3.8 THz (λ ≈ 79 µm) in pulsed mode up to a record high temperature of 137 K, whereas similar devices fabricated in SI-surface-plasmon waveguides had lower maximum lasing temperatures (∼92 K) due to the higher losses and lower confinement factors.This thesis describes the theory, design, fabrication, and testing of terahertz quantum cascade laser devices. A summary of theory relevant to design is presented, 3 including intersubband radiative transitions and gain, intersubband scattering, and coherent resonant tunneling transport using a tight-binding density matrix model. Analysis of the effects of the complex heterostructure phonon spectra on terahertz QCL design are considered. Calculations of the properties of various terahertz waveguides are presented and compared with experimental results. Various fabrication methods have been developed, including a robust metallic wafer bonding technique used to fabricate metal-metal waveguides. A wide variety of quantum cascade structures, both lasing and non-lasing, have been experimentally characterized, which yield valuable information about the transport ...

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“…The number of electromagnetic modes in a differential volume d 3 q in q space is 24) where n is the index of refraction at the frequency ω 0 = (E i − E f )/h, and c is the speed of light in a vacuum. As shown above, the spontaneous emission rate can be expressed in terms of the dipole matrix element, or the scaled oscillator strength …”

Section: Spontaneous Emission Lifetimementioning

confidence: 99%

Terahertz Quantum Cascade Lasers

Williams

¹

2008

Asia Optical Fiber Communication and Optoelectronic Exposition and Conference

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The development of the terahertz frequency range (1-10 THz, λ ≈ 30-300 µm) has long been impeded by the relative dearth of compact, coherent radiation sources of reasonable power. This thesis details the development of quantum cascade lasers (QCLs) that operate in the terahertz with photon energies below the semiconductor Reststrahlen band. Photons are emitted via electronic intersubband transitions that take place entirely within the conduction band, where the wavelength is chosen by engineering the well and barrier widths in multiple-quantum-well heterostructures. Fabrication of such long wavelength lasers has traditionally been challenging, since it is difficult to obtain a population inversion between such closely spaced energy levels (hω ≈ 4-40 meV), and because traditional dielectric waveguides become extremely lossy due to free carrier absorption.This thesis reports the development of terahertz QCLs in which the lower radiative state is depopulated via resonant longitudinal-optical phonon scattering. This mechanism is efficient and temperature insensitive, and provides protection from thermal backfilling due to the large energy separation (∼36 meV) between the lower radiative state and the injector. Both properties are important in allowing higher temperature operation at longer wavelengths. Lasers using a surface plasmon based waveguide grown on a semi-insulating (SI) GaAs substrate were demonstrated at 3.4 THz (λ ≈ 88 µm) in pulsed mode up to 87 K, with peak collected powers of 14 mW at 5 K, and 4 mW at 77 K.Additionally, the first terahertz QCLs have been demonstrated that use metalmetal waveguides, where the mode is confined between metal layers placed immediately above and below the active region. These devices have confinement factors close to unity, and are expected to be advantageous over SI-surface-plasmon waveguides, especially at long wavelengths. Such a waveguide was used to obtain lasing at 3.8 THz (λ ≈ 79 µm) in pulsed mode up to a record high temperature of 137 K, whereas similar devices fabricated in SI-surface-plasmon waveguides had lower maximum lasing temperatures (∼92 K) due to the higher losses and lower confinement factors.This thesis describes the theory, design, fabrication, and testing of terahertz quantum cascade laser devices. A summary of theory relevant to design is presented, 3 including intersubband radiative transitions and gain, intersubband scattering, and coherent resonant tunneling transport using a tight-binding density matrix model. Analysis of the effects of the complex heterostructure phonon spectra on terahertz QCL design are considered. Calculations of the properties of various terahertz waveguides are presented and compared with experimental results. Various fabrication methods have been developed, including a robust metallic wafer bonding technique used to fabricate metal-metal waveguides. A wide variety of quantum cascade structures, both lasing and non-lasing, have been experimentally characterized, which yield valuable information about the transport ...

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“…Such a mechanism of the nearly periodic electron motion leads to electric field induced resonances in high-frequency conductivity [the so-called optical phonon transient time resonance (OPTTR)] [13]. The OPTTR provides an operating principle for electrically pumped semiconductor sub-THz and THz sources [13], that has been practically realized in n-InP crystals [14].…”

Section: Introductionmentioning

confidence: 99%

High-frequency response of GaN in moderate electric and magnetic fields: interplay between cyclotron and optical phonon transient time resonances

Syngayivska¹,

Korotyeyev²,

Kochelap³

2013

Semicond. Sci. Technol.

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Abstract. We have studied the high-frequency properties of the non-equilibrium electron gas in GaN samples subjected to electric and magnetic fields. Spectra of the complex tensor of the dynamical mobility have been calculated for THz frequency range. For the compensated GaN and low temperatures, in the intervals of electric fields of the few kV /cm and magnetic fields of the few T the existence of the cyclotron and optical phonon transit-time resonances has been identified. We have shown that interplay of two resonances gives rise to specific spectra of THz transmission and absorption (or gain). We suggest that experimental investigation of these effects will facilitate elaboration of field controlled devices for THz optoelectronics.

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Far-infrared semiconductor lasers

Cited by 64 publications

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Terahertz quantum-cascade lasers

Terahertz quantum-cascade lasers

Terahertz Quantum Cascade Lasers

High-frequency response of GaN in moderate electric and magnetic fields: interplay between cyclotron and optical phonon transient time resonances

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