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Electrical activation studies of Si-implanted GaN layers on sapphire were made as a function of annealing temperature (1100–1400 °C). For an ion dose of 1.0×1014 cm-2, the optimum annealing temperature was 1400 °C, exhibiting a nearly 100% electrical activation efficiency and a low sheet resistance of ∼450 Ω/square at room temperature. From variable temperature Hall-effect measurements, Si-implanted GaN films annealed below 1200 °C displayed deep ionization levels of ∼280 meV, whereas samples annealed above 1300 °C had shallow ones of ∼11 meV. For lateral Schottky diodes fabricated on Si-implanted GaN layers annealed below 1200 °C, capacitance frequency and thermal admittance measurements showed a typical dispersion effect characteristic of a single deep donor with an activation energy of ∼133 meV. These results illustrate that deep donor levels created by the Si implantation in GaN layers apparently annihilate and transit to shallow levels produced by the Si ion substitution for Ga in the GaN lattice (SiGa) by annealing at temperature greater than ∼1300 °C at these doses. [ABSTRACT FROM AUTHOR]

The fabrication of GaN merged p–i–n/Schottky (MPS) diodes using Si+ ion implantation into p-epi layers on bulk, free-standing GaN substrates is reported. Diode diameters from 50 to 500 μm were investigated. These initial MPS diodes show larger turn-on voltage (∼30 V) than the unimplanted p–i–n diodes (∼10 V) fabricated on the same wafer but lower reverse leakage current density. The Si+ implant activation efficiency is ∼25% for 1150 °C anneals, reaching ∼30% for 1200 °C anneals. [Copyright &y& Elsevier]

Type conversion of p-GaN by direct Si+ ion implantation and subsequent annealing was demonstrated by the fabrication of lateral Schottky diodes. The Si+ activation percentage was measured as a function of annealing time (30--300 sec) and temperature (1,000--1,200°C), reaching a maximum of ∼30% for 1,200°C, 2-min anneals. The resulting n-type carrier concentration was 1.1 x 1018 cm-3 for a moderate Si+ ion dose of ∼2 x 1014 cm-2. The lateral Schottky diodes displayed a negative temperature coefficient of -0.15 V.K for reverse breakdown voltage. [ABSTRACT FROM AUTHOR]

Junction termination extension (JTE) structures for GaN power Schottky rectifiers were investigated using a quasi-three-dimensional simulator. The use of single JTE edge termination was found to produce an almost fivefold increase in reverse breakdown voltage (VB) over an unterminated rectifier fabricated on the same bulk GaN substrate. The use of p+ guard rings or planar junction termination with oxide field plates also offers significant enhancements in VB relative to unterminated rectifiers. VB was found to be a strong function of the JTE doping concentration and the p+ guard-ring spacing. [Copyright &y& Elsevier]

Multiple-energy Si+ implantation in the range 30–360 keV into Al0.13Ga0.87N for n-type doping was carried out at room temperature, followed by annealing at 1150–1375 °C for 5 min. Activation efficiencies close to 100% were obtained for ion doses of 1.0×1015 cm-2 after annealing at 1375 °C, with a resulting sheet resistance of 74 Ω/square. By sharp contrast, the activation efficiency at 1150 °C was only 4% for this dose, with a sheet resistance of 1.63×104 Ω/square. The activation efficiency was also a function of dose, with a maximum activation percentage of only 55% for lower doses of 1.0×1014 cm-2 annealed at 1375 °C. This is due to the comparatively larger effect of compensating acceptors at the lower dose and is also lower than the corresponding activation of Si in pure GaN under these conditions (78%). The measurement temperature dependence of sheet carrier density showed an activation energy of 23 meV, consistent with the ionization energy of Si in AlGaN. [ABSTRACT FROM AUTHOR]

Si+ implantation at multiple ion energies (30–360 keV) into GaN for n-type doping was carried out at substrate temperatures from 27 to 700 °C, followed by annealing at 1150–1400 °C for 5 min. At total doses of 2.0×1014 cm-2 (corresponding to an approximately uniform Si concentration of ∼4×1018 cm-3), the use of elevated implant temperature does not produce improved electrical characteristics. For anneal temperatures below ∼1300 °C, the resulting sheet resistance of the GaN implanted at 700 °C was approximately a factor of 2 higher than for room-temperature implantation, mainly through a lower sheet carrier density. At the higher annealing temperatures (>1300 °C), elevated implant temperature produced similar sheet resistances to implantation carried out at room temperature. For annealing at 1300 °C, the lowest sheet resistances (<700 Ω/□) and highest activation efficiencies (∼65%) were obtained for implant temperatures <400 °C. The most plausible explanation is that at these doses, SiGa (i.e., donor state) site occupation is not a strong function of the initial amount of damage created by the implantation. [ABSTRACT FROM AUTHOR]

We report the initial demonstration of an enhancement mode MgO/p-GaN metal-oxide-semiconductor field-effect transistor (MOSFET) utilizing Si+ ion-implanted regions under the source and drain to provide a source of minority carriers for inversion. The breakdown voltage for an 80-nm-thick MgO gate dielectric was ∼14 V, corresponding to a breakdown field strength of 1.75 MV cm-1 and the p-n junction formed between the p-epi and the source had a reverse breakdown voltage >15 V. Inversion of the channel was achieved for gate voltages above 6 V. The maximum transconductance was 5.4 μS mm-1 at a drain-source voltage of 5 V, comparable to the initial values reported for GaAs MOSFETs. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The performance of a 9 device array of 500 × 500 μm2 GaN p-i-n rectifiers fabricated on epitaxial layers grown on a free-standing GaN template is reported. The forward turn-on voltage was ∼5.5 V at 25 °C, with an on-state resistance of ∼5 × 10−3 Ω cm2. The total forward current was 1 A at ∼8.8 V and 2.6 A at 18 V. The power figure-of-merit for the array, VB2/RON, was 0.69 MW cm−2, with a reverse recovery time of &les;300 ns. The individual p-i-n rectifiers were interconnected using electroplated Au and clamped in a Cu pressure pack for thermal management. [Copyright &y& Elsevier]