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Type: Article × Subject: gallium nitride ×

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    Temperature-Dependent Charge Carrier Diffusion in [0001¯] Direction of GaN Determined by Luminescence Evaluation of Buried InGaN Quantum Wells
    (Weinheim : Wiley-VCH, 2020) Netzel, Carsten; Hoffmann, Veit; Tomm, Jens W.; Mahler, Felix; Einfeldt, Sven; Weyers, Markus
    Temperature-dependent transport of photoexcited charge carriers through a nominally undoped, c-plane GaN layer toward buried InGaN quantum wells is investigated by continuous-wave and time-resolved photoluminescence spectroscopy. The excitation of the buried InGaN quantum wells is dominated by charge carrier diffusion through the GaN layer; photon recycling contributes only slightly. With temperature decreasing from 310 to 10 K, the diffusion length in [0001⎯⎯] direction increases from 250 to 600 nm in the GaN layer. The diffusion length at 300 K also increases from 100 to 300 nm when increasing the excitation power density from 20 to 500 W cm−2. The diffusion constant decreases from the low-temperature value of ∼7 to 1.5 cm2 s−1 at 310 K. The temperature dependence of the diffusion constant indicates that the diffusivity at room temperature is limited by optical phonon scattering. Consequently, higher diffusion constants in GaN-based devices require a reduced operation temperature. To increase diffusion lengths at a fixed temperature, the effective recombination time has to be prolonged by reducing the number of nonradiative recombination centers.
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    Effects of post metallization annealing on Al2O3 atomic layer deposition on n-GaN
    (Bristol : IOP Publ., 2022) Tadmor, Liad; Brusaterra, Enrico; Treidel, Eldad Bahat; Brunner, Frank; Bickel, Nicole; Vandenbroucke, Sofie S. T.; Detavernier, Christophe; Würfl, Joachim; Hilt, Oliver
    The chemical, physical and electrical properties and the robustness of post metallization annealed Al2O3 atomic layers deposited on n-type GaN are investigated in this work. Planar metal insulator capacitors are used to demonstrate a gate-first with following ohmic contacts formation at elevated temperature up to 600 °C process flow. X-ray photoelectron spectroscopy indicates that no new bonds in the Al2O3 layer are formed due to exposure to the elevated annealing temperature. X-ray diffraction measurements show no crystallization of the oxide layer. Atomic force microscopy shows signs of degradation of the sample annealed at 600 °C. Electrical measurements indicate that the elevated annealing temperature results in an increase of the oxide depletion and the deep depletion capacitances simultaneously, that results in a reduction of the flat band voltage to zero, which is explained by fixed oxide charges curing. A forward bias step stress capacitance measurement shows that the total number of induced trapped charges are not strongly affected by the elevated annealing temperatures. Interface trap density of states analysis shows the lowest trapping concentration for the capacitor annealed at 500 °C. Above this temperature, the interface trap density of states increases. When all results are taken into consideration, we have found that the process thermal budget allows for an overlap between the gate oxide post metallization annealing and the ohmic contact formation at 500 °C.