28 research outputs found

    Enhancement of Intersubband Absorption in GaInN/AlInN Quantum Wells

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    GaInN/AlInN multiple quantum wells were grown by RF plasma--assisted molecular beam epitaxy on (0001) GaN/sapphire substrates. The strain-engineering concept was applied to eliminate cracking effect and to improve optical parameters of intersubband structures grown on GaN substrates. The high quality intersubband structures were fabricated and investigated as an active region for applications in high-speed devices at telecommunication wavelengths. We observed the significant enhancement of intersubband absorption with an increase in the barrier thickness. We attribute this effect to the better localization of the second electron level in the quantum well. The strong absorption is very important on the way to intersubband devices designed for high-speed operation. The experimental results were compared with theoretical calculations which were performed within the electron effective mass approximation. A good agreement between experimental data and theoretical calculations was observed for the investigated samples

    Zero Field Spin Splitting in GaN/AlGaN Heterostructures Probed by the Weak Antilocalization

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    We present the magnetoconductivity measurements of a high mobility two-dimensional electron gas confined at GaN/AlGaN interface. The sensitive measurements of low field conductivity revealed both quantum corrections, the weak localization and antilocalization effects. It indicates the importance of the spin-orbit coupling in this wide band gap material. The analysis of the data provided the information about the temperature dependence of the dephasing time and total spin-orbit relaxation time. The conduction band spin splitting energy amounts to 0.23 meV and 0.35 meV at electron densities 2.2×1012cm22.2×10^{12} cm^{-2} and $5.7×10^{12} cm^{-2}, respectively

    Electron-Electron Interaction Effects in Quantum Hall Regime of GaN/AlGaN Heterostructures

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    We measured the activation of resistivity at quantum Hall minima in high mobility two-dimensional electron gas confined at AlGaN/GaN interface. The effective g-factor and effective mass was deduced. The electron-electron interactions modify both quantities compared to their bare band values. It is found that the influence of interactions is much more pronounced onto g-factor than effective mass. The relative spin susceptibility was also calculated and compared with available theories. The best agreement was found with the ideal two-dimensional gas model in random phase approximation

    Influence of strain on the indium incorporation in (0001) GaN

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    The incorporation of indium in GaN (0001) surfaces in dependence of strain is investigated by combining molecular-beam epitaxy (MBE) growth, quantitative transmission electron microscopy, and density-functional theory (DFT) calculations. Growth experiments were conducted on GaN, as well as on 30±2 partially relaxed In0.19Ga0.81N buffer layers, serving as substrates. Despite the only 0.6 larger in-plane lattice constant of GaN provided by the buffer layer, our experiments reveal that the In incorporation increases by more than a factor of two for growth on the In0.19Ga0.81N buffer, as compared to growth on GaN. DFT calculations reveal that the decreasing chemical potential due to the reduced lattice mismatch stabilizes the In-N bond at the surface. Depending on the growth conditions (metal rich or N rich), this promotes the incorporation of higher In contents into a coherently strained layer. Nevertheless, the effect of strain is highly nonlinear. As a consequence of the different surface reconstructions, growth on relaxed InxGa1-xN buffers appears more suitable for metal-rich MBE growth conditions with regard to achieving higher In compositions. © 2020 American Physical Society

    Waveguide Design for Long Wavelength InGaN Based Laser Diodes

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    One-dimensional optical waveguide calculations were performed to study the dependence of waveguide design on confinement factor (Γp) and optical losses (αi\alpha_i) of nitride laser diodes for emission wavelength ranging from 405 nm to 520 nm. We found that the conventional waveguide design containing GaN waveguide and AlGaN cladding layers known from violet laser diode does not support sufficient confinement of the optical mode for long wavelength devices (λ > 450 nm). We proposed a new design consisting of a thick InGaN waveguide which enhances the confinement. We compared the theoretical predictions with laser diodes grown by plasma assisted molecular beam epitaxy

    Electrostatic Gates for GaN/AlGaN Quantum Point Contacts

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    We report on AlGaN/GaN quantum point contacts fabricated by using e-beam lithography and dry ion etching. The tunable nano-constrictions are defined by the integration of side and top gates in a single device. In this configuration, the planar gates are located on the both sides of a quantum channel and the metallic top gates, which cover the active region, are separated from the substrate by an insulating and passivating layers of HfO2HfO_2 or Al2O3//HfO2Al_2O_3//HfO_2 composite. The properties of devices have been tested at T = 4.2 K. For side gates we have obtained a very small surface leakage current Ig<1011I_g < 10^{-11} A at gate voltages Vg|V_g| < 2 V, however, it is not enough to close the quantum channel. With top gates we have been able to reach the pinch-off voltage at VgV_g = - 3.5 V at a cost of Ig106AI_g ≈ 10^{-6} A, which has been identified as a bulk leakage current