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A high-resistance buffer layer is critical for GaN-based high electron mobility transistors (HEMTs) to suppress the drain leakage current and pre-mature device breakdown. A typical method to obtain the HR buffer layers is the acceptor impurity doping that is able to provide holes to compensate the background electrons in the buffer layers. However, the intentional doped acceptor impurities such as Mg, Fe and C will result in current collapse in GaN-based HEMTs. To address this issue, in this work, we employed a polarization doping method of holes by Al-composition grading instead of the acceptor impurity doping. The sheet resistance of the GaN-based buffer layer significantly increased due to the holes generated by the polarization field. (a) Structures of the three samples; (b) Schematic illustration of polarization-induced 3DHG in (0001)-oriented graded AlGaN layer; (c) The square resistance of the three samples calculated by using CTLM. [ABSTRACT FROM AUTHOR]

In this paper, we report an experimental observation of the two-stage turn-on characteristic in normally-OFF Al2O3/GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) on Si substrate. The impact of oxide/GaN interface traps with different energy levels on the switching behavior of the device was extensively examined by simulation and verified by measurements. The interface traps at 0.4 eV below the bottom of the conduction band (Eit = EC-0.4 eV) of GaN buffer with a density of Dit = 6.5 x 1012 cm-2 was identified responsible for the ob- served two-stage turn-on characteristic. The weak Fermi-level pinning (WFLP) induced by the dynamic electron filling of interface traps may hamper the electron from accumulating in the Al2O3/GaN MOS-channel and then manifests a premature turn-on during the switching-on process. [ABSTRACT FROM AUTHOR]

In recent years, different power transistors have been developed in silicon carbide (SiC) and gallium nitride (GaN) as replacements for silicon based IGBTs. This paper presents a simulation comparison of the static and dynamic performance of silicon IGBTs with different SiC and GaN based lateral and vertical power transistors (HEMT, MOSFET and IGBT) with breakdown voltage ratings between 1.2 kV to 15 kV. The strengths and weaknesses of different technologies which make them suitable at different voltage levels have been discussed. [ABSTRACT FROM AUTHOR]

In this paper we report on the impact that the quantum well growth temperature has on the internal quantum efficiency and carrier recombination dynamics of two sets of InGaN/GaN multiple quantum well samples, designed to emit at 460 and 530 nm, in which the indium content of the quantum wells within each sample set was maintained. Measurements of the internal quantum efficiency of each sample set showed a systematic variation, with quantum wells grown at a higher temperature exhibiting higher internal quantum efficiency and this variation was preserved at all excitation power densities. By investigating the carrier dynamics at both 10 K and 300 K we were able to attribute this change in internal quantum efficiency to a decrease in the non-radiative recombination rate as the QW growth temperature was increased which we attribute to a decrease in incorporation of the point defects. [ABSTRACT FROM AUTHOR]

The mechanisms governing efficiency droop in an In0.18Ga0.82N/GaN multiple quantum well structure were investigated using a combination of ultrafast time-resolved terahertz and photoluminescence spectroscopy. From excitation fluence dependent studies, a reduction in the room temperature photoluminescence efficiency to 3% of its maximum value was observed for an excitation fluence of 0.96 mJcm-2. A correlation was found between the onset of efficiency droop and the emergence of a peak on the high-energy side of the quantum well emission with a 1/e decay time of 19.6 ps. These characteristics were attributed to the saturation of localised states and the population of higher energy delocalised states. Time-resolved studies revealed different scaling behaviours between the terahertz and photoluminescence decay dynamics, suggesting that the saturation of localised hole states may be playing a part in the onset of efficiency droop. [ABSTRACT FROM AUTHOR]

In this work, the Schottky-on-heterojunction light-emitting diodes (SoH-LED) are monolithically integrated with the AlGaN/GaN high-electron-mobility transistors (HEMT) on an AlGaN/GaN-on-Si platform commonly used for GaN lateral electronic devices. The on-chip electro-optic modulation is realized in a single device fabricated using HEMT-compatible process. Also, SoH-LED arrays are fabricated to demonstrate the on-chip addressable functionality with each SoH-LED pixel in the array individually controlled by the integrated HEMT. High-resolution micro-scale SoH-LED seven-segment displays are demonstrated to show the potential of using SoH-LEDs as a robust alternative for micro flat-panel displays. [ABSTRACT FROM AUTHOR]

In this work we employ terahertz (THz) ellipsometry to determine two-dimensional electron gas (2DEG) density, mobility and effective mass in AlGaN/GaN high electron mobility transistor structures grown on 4H-SiC substrates. The effect of the GaN interface exposure to low-flow-rate trimethylaluminum(TMA) on the 2DEG properties is studied. The 2DEGeffectivemass and sheet density are determined to be in the range of 0.30-0.32m0 and 4.3-5.5 x 1012 cm-2, respectively. The 2DEG effective mass parameters are found to be higher than the bulk effective mass of GaN, which is discussed in view of 2DEG confinement. It is shown that exposure to TMA flow improves the 2DEG mobility from 2000 cm²/Vs to values above 2200 cm²/Vs. A record mobility of 2332±61 cm²/Vs is determined for the sample with GaN interface exposed to TMA for 30 s. This improvement in mobility is suggested to be due to AlGaN/GaN interface sharpening causing the reduction of interface roughness scattering of electrons in the 2DEG. [ABSTRACT FROM AUTHOR]

In this paper, we presented AlGaN/GaN MIS-HEMT with a 6-nm ALD La2O3 as gate insulator. The gate leakage current had been greatly reduced at both positive and negative bias by using La2O3 gate dielectric. Threshold voltage for MIS-HEMT moved +1 V toward positive direction compared with the Schottky gate HEMT (HEMT) demonstrating the negatively fixed charges at La2O3/AlGaN interface. Besides, the transconductance of MIS-HEMT was not degraded. The stability of fixed and trap state introduced by La2O3 gate dielectric was discussed. [ABSTRACT FROM AUTHOR]