Al x Ga 1−x N  (x=0–0.25) Schottky rectifiers were fabricated in a lateral geometry employing p+-implanted guard rings and rectifying contact overlap onto an SiO2 passivation layer. The reverse breakdown voltage (VB) increased with the spacing between Schottky and ohmic metal contacts, reaching 9700 V for Al0.25Ga0.75N and 6350 V for GaN, respectively, for 100 μm gap spacing. Assuming lateral depletion, these values correspond to breakdown field strengths of ⩽9.67×105 V cm−1, which is roughly a factor of 20 lower than the theoretical maximum in bulk GaN. The figure of merit (VB)2/RON, where RON is the on-state resistance, was in the range 94–268 MW cm−2 for all the devices.

Multi-quantum-well GaN/InGaN heterojunction diodes prepared by metalorganic chemical vapor deposition on sapphire showed effects of strong tunneling in their I–V characteristics. The space charge region was shown to be located in the GaN/InGaN superlattice (SL). The injection of moderately high forward currents through the structure for several hours enhanced the overall tunneling through the structure and facilitated faster tunneling between the layers in the GaN/InGaN SL. These results may have relevance to the aging characteristics of light-emitting diodes under bias.

The fabrication of a wide variety of GaN-based photonic and electronic devices depends on dry etching, which typically requires ion-assisted removal of the substrate material. Under conditions of both high plasma flux and energetic ion bombardment, GaN etch rates greater than 0.5 νm/min and anisotropic etch profiles are readily achieved in Inductively Coupled Plasma (ICP) etch systems. Unfortunately, under these conditions plasma-induced damage often occurs. Attempts to minimize such damage by reducing the ion energy or increasing the chemical activity in the plasma often result in a loss of etch rate or profile control which can limit dimensional control and reduce the utility of the process for device applications requiring anisotropic etch profiles. It is therefore necessary to develop plasma etch processes which couple anisotropy for critical dimension and sidewall profile control and high etch rates with low-damage for optimum device performance. In this study we report changes in source resistance, reverse breakdown voltage, transconductance, and drain saturation current for GaN MESFET structures exposed to an Ar ICP plasma. In general, device performance was sensitive to ion bombardment energy and ion flux.

GaN-based metal oxide semiconductor field effect transistors ͑MOSFETs͒ were demonstrated using a stacked gate oxide consisting of single-crystal Gd 2 O 3 and amorphous SiO 2 . Gd 2 O 3 provides a good oxide/semiconductor interface and SiO 2 reduces the gate leakage current and enhances oxide breakdown voltage. Charge modulation of the n-channel depletion mode MOSFET was achieved for gate voltage from ϩ2 to Ϫ4 V. The source-drain breakdown voltage exceeded 80 V. An intrinsic transconductance of 61 mS/mm was obtained at a gate-source and drain-source bias of Ϫ0.5 and 20 V, respectively. This is the first demonstration of epitaxial Gd 2 O 3 growth on GaN and the first use of Gd 2 O 3 as an insulating layer for nitride electronic device applications.

GaN metal oxide semiconductor diodes were demonstrated utilizing Sc 2 O 3 as the gate oxide. Sc 2 O 3 was grown at 100°C on MOCVD grown n-GaN layers in a molecular beam epitaxy system, using a scandium elemental source and an electron cyclotron resonance oxygen plasma. Ar/Cl 2 based discharges were used to remove Sc 2 O 3 , to expose the underlying n-GaN for ohmic metal deposition in an inductively coupled plasma system. Electron beam deposited Ti/Al/Pt/Au and Pt/Au were utilized as ohmic and gate metallizations, respectively. An interface trap density of 5 ϫ 10 11 eV Ϫ1 cm Ϫ2 was obtained with the Terman method. Conductance-voltage measurements were also used to estimate the interface trap density and a slightly higher value was obtained as compared to the Terman method. Results of capacitance measurements at elevated temperature ͑up to 300°C͒ indicated the presence of deep states near the interface.GaN is regarded as having tremendous potential for applications in high-temperature, high-power, and high-speed electronic devices. 1,2 Though it has a large bandgap, the device performance degrades at higher temperatures due to high gate leakage resulting from limited Schottky barrier height. Many insulators, such as Ga 2 O 3 (Gd 2 O 3 ), AlN, SiO 2 , or Si 3 N 4, have been proposed for use in GaN-based metal oxide semiconductor field effect transistor ͑MOSFET͒ structures. 2-13 Some of them are known to have very high breakdown fields, but they all have a large lattice mismatch, resulting in a relatively high interface state density for crystalline oxides. For example, Gd 2 O 3 , which has a bandgap of 5.3 eV, has a large lattice mismatch of ϳ20% to GaN. Sc 2 O 3 has a similar bixbyite structure but also has a larger bandgap of 6.3 eV and a smaller lattice mismatch ϳ9.2%.In this work, scandium oxide (Sc 2 O 3 ) was deposited as gate insulator on GaN at 100°C to avoid crystalline formation. Electron microscopy showed the resulting interface to be smooth. MOS diodes were fabricated and characterized with current-voltage ͑IV͒, capacitance-voltage ͑CV͒, and conductance-voltage ͑GV͒ measurements. CV measurements under ultraviolet light and at higher temperature were also performed. ExperimentalScandium oxide was deposited epitaxially on ͑0001͒ GaN in a molecular beam epitaxy ͑MBE͒ system using elemental Sc and an electron cyclotron resonance ͑ECR͒ oxygen plasma. All oxide growths were performed in a modified Riber 2300 MBE equipped with a reflection high-energy electron diffraction ͑RHEED͒ system. Oxygen was supplied from a Wavemat MPDR 610 ECR plasma source ͑2.54 GHz͒ with 200 W forward power at 1 ϫ 10 Ϫ4 Torr oxygen pressure. A standard effusion cell operating at 1130-1170°C was used for the evaporation of the scandium. The oxide was either dry etched in an inductively coupled plasma ͑ICP͒ system or wet etched using hot H 2 SO 4 based solutions before depositing Ti/Al/ Pt/Au ͑200/700/400/1000 Å͒ ohmic contact. Pt/Au ͑200/1000 Å͒ was deposited as the gate contact.An HP 4145 parameter analyzer was employed to measure cur...