Design optimization of optically pumped terahertz lasers in stepped quantum wells

Abstract

Asymmetric stepped quantum wells (QWs) have been used in many optoelectronic devices. This paper proposes a modulation doping position at the edge of the stepped well to minimize the potential distortion caused by the doping. As a result, parasitic potential wells are eliminated, and the sensitivity of the energy levels to dopant concentrations is substantially reduced. We also suggest a stacked design to juxtapose two QW slabs in order to improve the waveguide mode overlap in optically pumped terahertz lasers using the structure. The percentage of overlap between the active QWs layers and the laser mode increases from 9.8% for a thinned substrate single slab scheme to 68.4% for the stacked double slabs, respectively, with two highly doped layers acting as plasma waveguide. A diffraction integral model is established to simulate the laser cavity tolerance to possible misalignment in the stacked design. Our modelling result shows that the diffraction loss due to small (few micrometre) misalignment or difference in slab length is negligible compared to other losses in the laser system.

Numerical design of AlGaN/GaN double quantum wells for intersubband absorption in the wavelength range ofλ9.3–10.6 μm

“…(2) the energy difference between the lower laser state and the ground state should be near 6 to the optical phonon energy (here, 0.091eV) in order to maximize the population inversion by the resonant LO-phononn scattering. Based on these two points, we design three and four-level systems, and further investigate intersubband absorption in these two systems, respectively.…”

Influence of thin AlAs layer insertion on intersubband optical transitions in GaAs/AlGaAs quantum- well structures

“…Terahertz (THz) intersubband lasers, which can be realized by optically pumped [1][2][3][4] or electrically excited [5][6] quantum well structures, is based on intersubband (ISB) transitions between specific subbands within a multiple quantum well (QW) heterostructure. The typical designs of the active region for the optically pumped THz lasers are based on a three-level system [7][8][9].…”

Intersubband absorption energy shifts in 3-level system for asymmetric quantum well terahertz emitters

“…[1][2][3][4][5][6][7][8][9] Those researches have aimed at making infrared lasers and photodetectors based on ISBTs. In order to overcome these shortcomings, another kind of THz generator by making use of asymmetric step quantum well structure is proposed [11][12][13] in which one has to consider 3-level model to realize population inversion between the first and second excited levels. 10 Among all kinds of THz radiators, THz quantum cascade laser ͑QCL͒ is a promising one due to its higher output power and monochromaticity, while, as well known, making QCL needs complicated technique procedure and high cost.…”

“…Recently, compact solid-state source of terahertz ͑THz͒ radiator attract great interests and efforts for its numerous potential applications in both imaging and wireless communications. Besides, optical pumping 11,14 allows great simplification in device design and fabrication compared to the electrical injection. In order to overcome these shortcomings, another kind of THz generator by making use of asymmetric step quantum well structure is proposed [11][12][13] in which one has to consider 3-level model to realize population inversion between the first and second excited levels.…”