Tokyo Institute of Technology · 공학
마사히로 아사다 교수의 연구실은 반도체 레이저 및 초고주파 소자에 대한 이론적 분석을 중심으로, 양자점, 양자우드, 양자홀 등 1D~3D 나노구조에서의 전자 상태와 광학적 특성 간의 상호작용을 깊이 있게 연구하고 있습니다. 특히 전자기계적 다이폴 모멘트, 비가역적 상관관계, 그리고 비가역적 스트레스 효과를 고려한 밀도행렬 이론을 기반으로 한 고성능 레이저의 이론적 설계와 성능 최적화를 추구합니다. 또한 레이저의 이득, 임계 전류 밀도, 그리고 고주파 동작 특성에 대한 정량적 분석을 통해 실용적 응용 가능성을 확보하고 있습니다.
표시된 성과는 수집된 데이터 기준으로 산출되며, 일부 차이가 있을 수 있습니다.
Gain and threshold current density are analyzed for quantum-box lasers where electrons are confined in quantum well three-dimensionally, based on the density-matrix theory of semiconductor lasers with relaxation broadening. The electronic dipole moment and its polarization dependence are first analyzed, and it is shown that the gain becomes maximum when the electric field of light is parallel to the longest side of the quantum box. Calculated gain is about 10 times that of bulk crystal for 100 Å
The linear gain and the intervalence band absorption are analyzed for quantum-well lasers. First, we analyze the electronic dipole moment in quantum-well structures. The dipole moment for the TE mode in quantum-well structures is found to be about 1.5 times larger at the subband edges than that of conventional double heterostructures. Also obtained is the difference of the dipole moment between TE and TM modes, which results in the gain difference between these modes. Then we derive the linear g
Resonant tunneling diodes (RTDs) have the potential for use as compact and coherent terahertz (THz) sources operating at room temperature. In this paper, sub-THz and THz oscillators with RTDs integrated on planar circuits are described. Fundamental oscillation up to 0.65 THz and harmonic oscillation up to 1.02 THz were obtained at room temperature in our recent study. Limiting factors for oscillation frequency and output power are theoretically analyzed including tunneling and transit-time effec
Abstract A large increase in oscillation frequency was achieved in resonant-tunneling-diode (RTD) terahertz oscillators by reducing the conduction loss. An n + -InGaAs layer under the air-bridge electrode connected to the RTD was observed to cause a large conduction loss for high-frequency current due to the skin effect. By introducing a new fabrication process removing the InGaAs layer, we obtained 1.92-THz oscillation, which extended the highest frequency of room-temperature electronic single
The density-matrix theory of semiconductor lasers with relaxation broadening model is finally established by introducing theoretical dipole moment into previously developed treatments. The dipole moment is given theoretically by the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k . p</tex> method and is calculated for various semiconductor materials. As a result, gain and gain-suppression for a variety of crystals covering wide wavelength region a
Gain is given theoretically for quantum-well wire lasers where electrons are confined one-dimensionally. Maximum gain is obtained for a quantum-well wire perpendicular to light propagation, due to anisotropy of the dipole moment. Although the density-of-states is infinite at subband edges, gain remains finite due to the intraband relaxation. Therefore, high gain can be obtained by reducing intraband scatterings. Gain in 100 Å×100 Å Ga 0.47 In 0.53 As/InP quantum-well wires is about twice that in
Intraband relaxation time, which causes spectral broadening of optical gain and spontaneous emission spectra, is estimated theoretically for quantum-well lasers. Carrier-carrier and carrier-longitudinal-optical (LO) phonon scattering mechanisms are considered, and it is shown that hole-hole, electron-hole, and hole-LO phonon scattering are dominant in spectral broadening. Intraband relaxation time determined by all of these mechanisms increases slightly with the decrease of well width. The depen
The temperature dependence of the threshold current of GaInAsP/InP lasers was considered in terms of linear gain, loss, and carder lifetime. The linear gain was calculated taking into account electronic intraband relaxation effects. The carrier lifetime, intraband relaxation time, loss in the active region, and dipole moment, all of which determine the threshold condition, were estimated from the experiments. The main loss mechanism which determines the temperature dependence of the differential
A compact source is important for various applications utilizing terahertz (THz) waves. In this paper, the recent progress in resonant-tunneling diode (RTD) THz oscillators, which are compact semiconductor THz sources, is reviewed, including principles and characteristics of oscillation, studies addressing high-frequency and high output power, a structure which can easily be fabricated, frequency tuning, spectral narrowing, different polarizations, and select applications. At present, fundamenta
Various factors influencing the temperature dependence of the threshold current of GaInAsP/InP lasers in the wavelength region of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.5-1.6\mu</tex> m were measured in terms of the gain, the loss, the spontaneous emission, and the carrier lifetime. The effects of the intervalence band absorption influence the differential quantum efficiency or the loss, while the nonradiative recombination and the carrie
A report is presented on the dependence of oscillation frequency on antenna length in resonant‐tunnelling‐diode terahertz (THz) oscillators integrated with slot antennas. The upper limit of the oscillation frequency was maximised at an optimum antenna length. The highest oscillation frequency obtained in the experiment was 1.55 THz for a 16 μm‐long antenna at room temperature.
We investigate the effect of intrinsic and extrinsic delay times on the oscillation characteristics of resonant-tunneling-diode (RTD) terahertz oscillators. The intrinsic delay time is composed of the electron dwell time in the resonant tunneling region and the electron transit time in the collector depletion region. We obtain and discuss the structure dependence of these factors in terms of the oscillation frequency and output power measured for RTD oscillators with different quantum-well and c
Power combining with array configuration is an effective method for high output power in oscillators with resonant tunneling diodes (RTDs) in subterahertz and terahertz range. In this paper, output power and stability are analyzed for coupled oscillator array of RTDs. The coupled van der Pol equations are derived from the equivalent circuit for two-element oscillator arrays at first, and the condition in which only the fundamental oscillation mode stably oscillates is shown. The oscillation freq
