A phonon scattering assisted injection and extraction based terahertz quantum cascade laser

A novel lasing scheme for terahertz quantum cascade lasers, based on consecutive phonon-photon-phonon emissions per module, is proposed and experimentally demonstrated. The charge transport of the proposed structure is modeled using a rate equation formalism. An optimization code based on a genetic algorithm was developed to find a four-well design in the $\mathrm{GaAs/Al_{0.25}Ga_{0.75}As}$ material system that maximizes the product of population inversion and oscillator strength at 150 K. The fabricated devices using Au double-metal waveguides show lasing at 3.2 THz up to 138 K. The electrical characteristics display no sign of differential resistance drop at lasing threshold, which suggests - thanks to the rate equation model - a slow depopulation rate of the lower lasing state, a hypothesis confirmed by non-equilibrium Green's function calculations.Comment: 11 pages, 10 figure

A phonon scattering assisted injection and extraction based terahertz quantum cascade laser

A novel lasing scheme for terahertz quantum cascade lasers, based on consecutive phonon-photon-phonon emissions per module, is proposed and experimentally demonstrated. The charge transport of the proposed structure is modeled using a rate equation formalism. An optimization code based on a genetic algorithm was developed to find a four-well design in the $\mathrm{GaAs/Al_{0.25}Ga_{0.75}As}$ material system that maximizes the product of population inversion and oscillator strength at 150 K. The fabricated devices using Au double-metal waveguides show lasing at 3.2 THz up to 138 K. The electrical characteristics display no sign of differential resistance drop at lasing threshold, which suggests - thanks to the rate equation model - a slow depopulation rate of the lower lasing state, a hypothesis confirmed by non-equilibrium Green's function calculations.Comment: 11 pages, 10 figure

Electrically switching transverse modes in high power THz quantum cascade lasers.

The design and fabrication of a high power THz quantum cascade laser (QCL), with electrically controllable transverse mode is presented. The switching of the beam pattern results in dynamic beam switching using a symmetric side current injection scheme. The angular-resolved L-I curves measurements, near-field and far-field patterns and angular-resolved lasing spectra are presented. The measurement results confirm that the quasi-TM(01) transverse mode lases first and dominates the lasing operation at lower current injection, while the quasi-TM(00) mode lases at a higher threshold current density and becomes dominant at high current injection. The near-field and far-field measurements confirm that the lasing THz beam is maneuvered by 25 degrees in emission angle, when the current density changes from 1.9 kA/cm(2) to 2.3 kA/cm(2). A two-dimension (2D) current and mode calculation provides a simple model to explain the behavior of each mode under different bias conditions

A case report and literature review of the late presenting congenital diaphragmatic hernia

Late presenting congenital diaphragmatic hernia is a disease associated with defective diaphragm and penetration of different organs into the thoracic cavity. In the present case, a 3-year-old boy was referred to our hospital complaining of acute abdominal pain. No other gastrointestinal symptoms including nausea, vomiting, or constipation were observed. The patient represented no respiratory problems such as dyspnea or respiratory distress syndrome. Radiograph of the thoracic and abdominal cavities showed bowel loops occupying the entire space of the left hemithorax and right-shifted mediastinum. The patient was referred to the pediatric surgery center. The defect was resolved by prompt surgical intervention. A follow-up radiograph within 6 months of surgery showed complete recovery. © 2018 Annals of Pediatric Surgery

Rate equation analysis of three phonon-photon-phonon terahertz quantum cascade lasers

A rate equation model is presented to analyze the performance of terahertz quantum cascade lasers based on consecutive phonon-photon-phonon emissions. Devices lased up to 128.5, 138, and 144 K at 2.5, 3.2 and 2.6 THz, respectively. \ua9 Optical Society of America.Peer reviewed: YesNRC publication: Ye

Effects of interface roughness scattering on device performance of indirectly pumped terahertz quantum cascade lasers

The impacts of interface roughness (IR) scattering on device performance of indirectly-pumped (IDP) terahertz quantum cascade lasers are studied. Three different active region designs with almost the same lasing frequency at threshold and comparable oscillator strength are experimentally investigated and the measurement data are analyzed and compared with numerical simulation. The simulation results show that all structures suffer from the detrimental effect of intersubband roughness scattering in terms of threshold current density, and probably operating temperature. The intrasubband IR scattering time could also to be a limiting factor in the IDP structures due to the employed high energetic barrier.Peer reviewed: YesNRC publication: Ye

Nanoscopically resolved dynamic charge-carrier distribution in operating interband cascade lasers

Abstract Dynamic charge carriers play a vital role in active photonic quantum/nanodevices, such as electrically pumped semiconductor lasers. Here we present a systematic experimental study of gain-providing charge-carrier distribution in a lasing interband cascade laser. The unique charge-carrier distribution profile in the quantum-well active region is quantitatively measured at nanometer scales by using a noninvasive scanning voltage microscopy technique. Experimental results clearly confirm the accumulation and spatial segregation of holes and electrons in the beating heart of the device. The measurement also shows that the charge-carrier density is essentially clamped in the presence of stimulated emission at low temperatures. The threshold charge-carrier density exhibits a linear but fairly weak temperature dependence, in contrast to the exponential temperature dependence of the threshold current. The experimental approach will lead to a deeper understanding of fundamental processes that govern the operation and performance of nanoelectronic devices, quantum devices and optoelectronic devices

Electronic temperatures of terahertz quantum cascade active regions with phonon scattering assisted injection and extraction scheme

We measured the lattice and subband electronic temperatures of terahertz quantum cascade devices based on the optical phonon-scattering assisted active region scheme. While the electronic temperature of the injector state (j=4) significantly increases by \u25b3T=Te 4 -TL 3c40 K, in analogy with the reported values in resonant phonon scheme (\u25b3T 3c70-110 K), both the laser levels (j=2,3) remain much colder with respect to the latter (by a factor of 3-5) and share the same electronic temperature of the ground level (j=1). The electronic population ratio n2/n1 shows that the optical phonon scattering efficiently depopulates the lower laser level (j=2) up to an electronic temperature Te 3c180 K. \ua9 2013 Optical Society of America.Peer reviewed: YesNRC publication: Ye

A high carrier injection terahertz quantum cascade laser based on indirectly pumped scheme

A Terahertz quantum cascade laser with a rather high injection coupling strength based on an indirectly pumped scheme is designed and experimentally implemented. To effectively suppress leakage current, the chosen quantum cascade module of the device is based on a five-well GaAs/Al[subscript 0.25]Ga[subscript 0.75]As structure. The device lases up to 151 K with a lasing frequency of 2.67 THz. This study shows that the effect of higher energy states in carrier transport and the long-range tunnel coupling between states that belong to non-neighbouring modules have to be considered in quantum design of structures with a narrow injector barrier. Moreover, the effect of interface roughness scattering between the lasing states on threshold current is crucial.Natural Sciences and Engineering Research Council of CanadaCanadian Foundation for InnovationCMC Microsystems (Firm)Ontario Research Foundatio

Effect of oscillator strength and intermediate resonance on the performance of resonant phonon-based terahertz quantum cascade lasers

We experimentally investigated the effect of oscillator strength (radiative transition diagonality) on the performance of resonant phonon-based terahertz quantum cascade lasers that have been optimized using a simplified density matrix formalism. Our results show that the maximum lasing temperature (T max) is roughly independent of laser transition diagonality within the lasing frequency range of the devices under test (3.2-3.7 THz) when cavity loss is kept low. Furthermore, the threshold current can be lowered by employing more diagonal transition designs, which can effectively suppress parasitic leakage caused by intermediate resonance between the injection and the downstream extraction levels. Nevertheless, the current carrying capacity through the designed lasing channel in more diagonal designs may sacrifice even more, leading to electrical instability and, potentially, complete inhibition of the devices lasing operation. We propose a hypothesis based on electric-field domain formation and competition/switching of different current-carrying channels to explain observed electrical instability in devices with lower oscillator strengths. The study indicates that not only should designers maximize Tmax during device optimization but also they should always consider the risk of electrical instability in device operation.Peer reviewed: YesNRC publication: Ye