Single-crystal gallium oxide (Ga 2 O 3) metal-oxide-semiconductor field-effect transistors were fabricated on a semi-insulating b-Ga 2 O 3 (010) substrate. A Sn-doped n-Ga 2 O 3 channel layer was grown by molecular-beam epitaxy. Si-ion implantation doping was performed to source and drain electrode regions for obtaining low-resistance ohmic contacts. An Al 2 O 3 gate dielectric film formed by atomic layer deposition passivated the device surface and significantly reduced gate leakage. The device with a gate length of 2 lm showed effective gate modulation of the drain current with an extremely low off-state drain leakage of less than a few pA/mm, leading to a high drain current on/off ratio of over ten orders of magnitude. A three-terminal off-state breakdown voltage of 370 V was achieved. Stable transistor operation was sustained at temperatures up to 250 C. V

The process of charge injection plays an important role in organic semiconductor devices. We review various experimental techniques that allow injection to be separated from other competing processes, and quantify the injection efficiency of a contact. We discuss the dependence of the injection efficiency on parameters such as the energy barrier at the interface, the carrier mobility of the organic semiconductor, its carrier density (doping level), the presence of mobile ions, and the sample geometry. Based on these findings, we outline guidelines for forming ohmic contacts and present examples of contact engineering in organic semiconductor devices.

No abstract

We describe the development of N-polar GaN-based high electron mobility transistors grown by N 2 plasma-assisted molecular beam epitaxy on C-face SiC substrates. High mobility AlGaN / GaN modulation-doped two-dimensional electron gas channels were grown, and transistors with excellent dc and small-signal performance were fabricated on these wafers. Large-signal dispersion was observed, and the trap states responsible for this were identified, and layer designs to remove the dispersive effects of these traps were demonstrated. Finally, an AlGaN-cap layer was used to reduce gate leakage in these devices, and a low-dispersion high breakdown voltage device was achieved. This detailed study of dispersion and leakage in N-polar GaN-based transistors establishes a technological base for further development of field effect devices based on N-polar III-nitrides.

The band alignment of Al2O3/n-Ga2O3 was investigated by x-ray photoelectron spectroscopy (XPS). With a band gap of 6.8 ± 0.2 eV measured for Al2O3, the conduction and valence band offsets at the interface were estimated to be 1.5 ± 0.2 eV and 0.7 ± 0.2 eV, respectively. The conduction band offset was also obtained from tunneling current in Al2O3/n-Ga2O3 (2¯01) metal-oxide-semiconductor (MOS) diodes using the Fowler-Nordheim model. The electrically extracted value was in good agreement with the XPS data. Furthermore, the MOS diodes exhibited small capacitance-voltage hysteresis loops, indicating the successful engineering of a high-quality Al2O3/Ga2O3 interface.

No abstract

This paper reviews the progress of N-polar (000 1) GaN high frequency electronics that aims at addressing the device scaling challenges faced by GaN high electron mobility transistors (HEMTs) for radio-frequency and mixed-signal applications. Device quality (Al, In, Ga)N materials for N-polar heterostructures are developed using molecular beam epitaxy and metalorganic chemical vapor deposition. The principles of polarization engineering for designing N-polar HEMT structures will be outlined. The performance, scaling behavior and challenges of microwave power devices as well as highly-scaled depletion-and enhancement-mode devices employing advanced technologies including self-aligned processes, n+ (In,Ga)N ohmic contact regrowth and high aspect ratio T-gates will be discussed. Recent research results on integrating N-polar GaN with Si for prospective novel applications will also be summarized.

Deep acceptor doping of β-Ga2O3 with Mg and N was demonstrated by implantation of the impurity ions into n-type bulk substrates. Systematic physical and electrical characterizations were performed to demonstrate recovery of the implantation-damaged crystals and electrical activation of the dopant atoms by thermal annealing at 1000–1200 °C in an N2 atmosphere. N was found to exhibit much lower thermal diffusivity than Mg, thus enabling the use of higher annealing temperatures to maximize N activation efficiency without significantly altering the impurity profile. Consequently, an n-Ga2O3/Ga2O3:N/n-Ga2O3 structure was capable of sustaining a much larger voltage across its end terminals than its Mg-doped counterpart. The development of an ion implantation technology for acceptor doping of β-Ga2O3 creates unique opportunities for designing and engineering a variety of high-voltage β-Ga2O3 devices.