Локализация носителей заряда в квантовых ямах InGaN/GaN, ограниченная объемным зарядом

The mechanism of carrier tunneling through the potential walls of InGaN/GaN quantum well in the p-n structures is studied by means of the deep center tunneling spectroscopy. A number of humps on the current and photocurrent tunneling spectra, as well as on the forward bias dependences of the intensity and the peak energy of photoluminescence band from the quantum well are detected. These findings allow us to propose a model of carrier localization in the quantum well that permit to relate the tunneling transparency of the potential walls of the QW to the space-charge of deep-level centers in the quantum well barriers and its changes under optical excitation and forward biasing of p-n structure.

Indium-contacted van der Waals gap tunneling spectroscopy for van der Waals layered materials

The electrical phase transition in van der Waals (vdW) layered materials such as transition-metal dichalcogenides and Bi2Sr2CaCu2O8+x (Bi-2212) high-temperature superconductor has been explored using various techniques, including scanning tunneling and photoemission spectroscopies, and measurements of electrical resistance as a function of temperature. In this study, we develop one useful method to elucidate the electrical phases in vdW layered materials: indium (In)-contacted vdW tunneling spectroscopy for 1T-TaS2, Bi-2212 and 2H-MoS2. We utilized the vdW gap formed at an In/vdW material interface as a tunnel barrier for tunneling spectroscopy. For strongly correlated electron systems such as 1T-TaS2 and Bi-2212, pronounced gap features corresponding to the Mott and superconducting gaps were respectively observed at T = 4 K. We observed a gate dependence of the amplitude of the superconducting gap, which has potential applications in a gate-tunable superconducting device with a SiO2/Si substrate. For In/10 nm-thick 2H-MoS2 devices, differential conductance shoulders at bias voltages of approximately ± 0.45 V were observed, which were attributed to the semiconducting gap. These results show that In-contacted vdW gap tunneling spectroscopy in a fashion of field-effect transistor provides feasible and reliable ways to investigate electronic structures of vdW materials.