This letter describes a new two-step electrode process on p-GaN and characteristics of GaN p-n junction diodes on free-standing GaN substrates with low specific ON-resistance R on and high breakdown voltage V B . We develop a two-step process for anode electrodes in order to avoid plasma damage to the p + -GaN contact layer during the sputtering process. The specific ON-resistance is further improved due to a new low-damage process. The breakdown voltage of the diodes with the field-plate (FP) structure is over 1100 V, and the leakage current was low, i.e., in the range of 10 −9 A. The specific ON-resistance of the diodes of 50 μm in diameter with the FP structure was 0.4 mΩ · cm 2 . Baliga's figure of merit (V 2 B /R on ) of 3.0 GW/cm 2 is obtained. These are the best values ever reported among those achieved by GaN p-n junction diodes on free-standing GaN substrates.Index Terms-Breakdown voltage, gallium nitride, power semiconductor devices.

In this letter, we describe the characteristics of Gallium Nitride (GaN) p–n junction diodes fabricated on free-standing GaN substrates with low specific on-resistance R on and high breakdown voltage V B. The breakdown voltage of the diodes with the field-plate (FP) structure was over 3 kV, and the leakage current was low, i.e., in the range of 10-4 A/cm2. The specific on-resistance of the diodes of 60 µm diameter with the FP structure was 0.9 mΩ·cm2. Baliga's figure of merit (V B 2/R on) of 10 GW/cm2 is obtained. Although a certain number of dislocations were included in the device, these excellent results indicated a definite availability of this material system for power-device applications.

Phone: þ81 42 387 6192, Fax: þ81 42 387 6122This report describes the fabrication and characteristics of GaN p-n junction diodes on free-standing GaN substrates with low dislocation density. We have demonstrated GaN p-n junction diodes with a unique field-plate (FP) structure. The breakdown voltage V B is further improved due to the FP structure and the low dislocation density. The breakdown voltage of a diode of 60 mm in diameter with the FP structure is over À1000 V, and the leakage current is below 10 À9 A until reaching the breakdown voltage. Even in larger diodes (100 and 200 mm in diameter) with FP, the breakdown voltage is over À800 V. However, the specific on-resistance R on is high due to damage by the plasma process of sputtering. The specific on-resistance is further improved due to using a low damage passivation film. As a result, a specific on-resistance of 1.2 mV Á cm 2 is obtained.

No abstract

The effect of extrinsic photon recycling (EPR) in p-type gallium nitride (p-GaN), namely, increased ionization ratio (R) of magnesium acceptors owing to radiative recombination, was quantitatively investigated. The lateral extension (L) of EPR was determined by using transmission-line-model (TLM) patterns, formed with GaN p–n junction epitaxial layers on free-standing substrates, as well as by using device simulation. With increasing vertical current (I V) of the p–n junction, lateral current (I L) in the p-GaN layer (magnesium concentration: N Mg = 5×1017 cm-3) was found to increase within L of 10 µm from the edge of the TLM electrodes; the measured I L corresponded to a large R, namely, 30%. This lateral extension will contribute to reducing base resistance and enhancing conductivity modulation of GaN bipolar power-switching devices for power-electronics applications.