High-Breakdown-Voltage and Low-Specific-on-Resistance GaN p–n Junction Diodes on Free-Standing GaN Substrates Fabricated Through Low-Damage Field-Plate Process

Abstract

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.

Formation of definite GaN p–n junction by Mg-ion implantation to n−-GaN epitaxial layers grown on a high-quality free-standing GaN substrate

“…The choice of the substrate was important because the most threading dislocations penetrated into the epitaxial layers in case of homo epitaxy. The epitaxial layers were grown using the same equipment as those reported in our previous paper which described GaN p-n diodes with very low on-resistance (0.9 X cm 2 ) and high breakdown voltage (>3000 V) [8]. Prior to ion implantation, the surface of the substrate was coated with a 30 nm thick SiN film so that the maximum concentration of Mg atoms should be located at the interface between the SiN cap and the surface of the GaN layer.…”

“…Surface morphologies were evaluated by an atomic-force microscope (AFM) and optical microscope. Vertical-structure p-n diodes were fabricated by depositing circular Pd electrodes (60-400 lm in diameter) on the surface of the Mg-implanted GaN layer and Ti/Al electrodes [8] at the bottom of the GaN substrate. Electroluminescence (EL) spectra were measured by Horiba's LabLAM HR-800 at room temperature.…”

Suppression of Current Leakage Along Mesa Surfaces in GaN-Based p-i-n Diodes

“…A plasma treatment with pure Ar actually does more surface damage since the measured breakdown voltage of 300 V is worse than that of the untreated control sample, 470 V. Apparently the pure physical bombardment of Ar ions yields no passivation. Any positive surface passivation starts when the chemical reaction component, CHF 3 , is added to the plasma. Yet an optimal mixture of Ar/CHF 3 ∼ 1 : 3 is found best for the surface passivation, at which a maximum breakdown voltage of 630 V is achieved.…”

“…GaN p-i-n rectifiers possess several advantages over Schottky barrier diodes, such as low leakage current, avalanche characteristics and reliability, and the best reported GaN p-i-n diodes grown on sapphire substrates have shown a Baliga's figure-of-merit (BFOM) of 545 MW/cm 2 [1]. The number goes up to 2.5 GW/cm 2 and more for devices grown on high-quality bulk GaN substrates though the substrate cost is a concern [1]- [3]. Conventional p-i-n rectifiers are fabricated in vertical or quasi-vertical structures, and mesa isolation with plasma etching is often required.…”

High-k Dielectric Passivation for GaN Diode with a Field Plate Termination

“…Contact holes were formed by ICP dry-etching. A Ti/Al electrode as a field plate was deposited by electron-beam deposition and formed by a liftoff process on the top surface [10]. The Ti/Al electrode was deposited by electron-beam deposition on the bottom surface of the n-GaN substrate.…”