Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

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We report recessed-gate Al2O3/AlGaN/GaN normally-OFF metal–oxide–semiconductor high-electron-mobility transistors (MOS-HEMTs) on 8 in. Si. The MOS-HEMTs showed a maximum drain current of 300 mA/mm with a high threshold voltage of +2.4 V. The quite low subthreshold leakage current (∼10−8 mA/mm) yielded an excellent ON/OFF current ratio (9 × 108) with a small, stable subthreshold slope of 74 mV/dec. An atomic-layer-deposited Al2O3 layer effectively passivates, as no significant drain current dispersions were observed. A high OFF-state breakdown voltage of 825 V was achieved for a device with a gate-to-drain distance of 20 µm at a gate bias of 0 V.

Al 2 O 3 deposited by atomic layer deposition (ALD) was focused as an insulator in metal-insulator-semiconductor (MIS) structures for GaN-based MIS-devices. As the oxygen precursors for the ALD process, water (H 2 O), ozone (O 3), and both H 2 O and O 3 were used. The chemical characteristics of the ALD-Al 2 O 3 surfaces were investigated by an X-ray photoelectron spectroscopy (XPS). After fabrication of MIS-diodes and MIS-high-electron-mobility transistors (MIS-HEMTs) with the ALD-Al 2 O 3 , their electrical properties were evaluated by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The threshold voltage of the C-V curves for MIS-diodes indicate that the fixed charge in the Al 2 O 3 layer is decreased by using both H 2 O and O 3 as the oxygen precursors. Furthermore, MIS-HEMTs with the H 2 O+O 3-based Al 2 O 3 showed the good DC I-V characteristics with the forward bias over 6 V, and the drain leakage current in the off-state region was suppressed by seven orders of magnitude.

Frequency dependent conductance measurements were employed to study the trapping effects of in-situ metal-organic chemical vapor deposition grown AlN/AlGaN/GaN metal-insulator-semiconductor heterostructures (MISHs). Conventional fitting method could not be used to explain the experimental parallel conductance (Gp/ω ) results. Alternatively, experimental Gp/ω values were resolved into two fitting curves for gate voltages (−1.2 to −1.8 V) near the threshold voltage (Vth) by a fitting model. In the low frequency region (≤50 kHz), the Gp/ω values can be fitted into a single curve. On the other hand, in the high frequency region, two fitting curves were necessary. The results using this model explicitly yielded two types of traps existing in the AlN/AlGaN/GaN MISHs, one due to the insulating AlN layer and the other caused by the AlGaN barrier layer.

We report novel GaN fully vertical p–n diode on Si grown by metalorganic chemical vapor deposition. The thick strained layer superlattice is effective in controlling a doping level of 1016 cm−3 in an n−-GaN drift layer. The GaN p–n diode exhibits a differential on-resistance R on of 7.4 mΩ cm2, a turn-on voltage of 3.4 V, and a breakdown voltage V B of 288 V. The corresponding Baliga’s figure of merit (FOM) is 11.2 MW/cm2. A good FOM value for the GaN-on-Si vertical p–n diode is realized for a drift layer thickness of 1.5 µm without using substrate removal technology.

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