High voltage (450 V) GaN Schottky rectifiers

Abstract

We fabricated high standoff voltage ͑450 V͒ Schottky rectifiers on hydride vapor phase epitaxy grown GaN on sapphire substrate. Several Schottky device geometries were investigated, including lateral geometry with rectangular and circular contacts, mesa devices, and Schottky metal field plate overlapping a SiO 2 layer. The best devices were characterized by an ON-state voltage of 4.2 V at a current density of 100 A/cm 2 and a saturation current density of 10 Ϫ5 A/cm 2 at a reverse bias of 100 V. From the measured breakdown voltage we estimated the critical field for electric breakdown in GaN to be (2.2Ϯ0.7)ϫ10 6 V/cm. This value for the critical field is a lower limit since most of the devices exhibited abrupt and premature breakdown associated with corner and edge effects. © 1999 American Institute of Physics. ͓S0003-6951͑99͒02409-2͔Wide band gap materials, primarily SiC and GaN, have recently attracted a lot of interest for applications in high power and high temperature electronics. Although the processing technology for SiC is more mature, GaN offers several advantages. First, there are various device possibilities using GaN/AlGaN heterojunctions which are not available in the SiC system. Second, the availability of cheap and efficient hydride vapor phase epitaxy ͑HVPE͒ growth technology achieving growth rates in excess of 100 m/h, have produced thick, high quality GaN layers on sapphire. 1 Third, by using AlGaN layers, one can take advantage of a larger band gap to achieve higher critical electric fields than in GaN alone.In this study, we focus on the fabrication of high voltage, GaN based Schottky rectifiers and the measurement of the critical field for electric breakdown. The critical field for electric breakdown is one of the most significant parameters in the design and performance of high power devices. It directly influences the required thickness of the standoff region in the Schottky rectifier and bipolar devices, such as the thyristor. Since the thickness of the standoff region sets the resistivity of the device, it will determine power dissipation and maximum current density of the device. 2,3 In previous studies, Schottky diodes have been fabricated on GaN using a variety of elemental metals including Pd and Pt, 4,5 , Au, Cr, and Ni,6,7 , and Mo and W. 8 More details on the metal-GaN contact technology can be found in Ref. 9.In this work, Schottky rectifiers were fabricated on 8-10 m thick GaN layers grown by HVPE on sapphire, where the electron concentration changes with the distance from the GaN/sapphire interface. We carried out conductivity and Hall measurements on a series of HVPE GaN films of varying thickness ranging from 0.07 to 9.2 m, and fitted the data to a two layer model. [10][11][12][13] From the model, we concluded that the GaN films consisted of a low conductivity, low electron concentration, 8-10 m thick top layer on a very thin (Ͻ100 nm), highly conductive, high electron concentration bottom layer. The electron concentrations and mobilities in the thin interface layer and thic...

Ni based planar Schottky diodes on gallium nitride (GaN) grown on sapphire

“…Among them, gallium nitride has gained attention due to its high band gap value (~3.4 eV at room temperature [1]) that makes it goes intrinsic at much higher temperature than Si, but also due to its high saturation velocity (3x10 7 cm/s, higher than for SiC [2]) and high critical electric field (≥4x10 6 V/cm) allowing to reach larger breakdown voltage values [3]. For the last few years, it has already found applications in topics such as optoelectronics devices, blue to green lightemitting diodes (LEDs), laser diodes (LDs), detectors or high electron mobility transistors (HEMTs) [4][5][6].…”

Electrical Properties and Carrier Transport Mechanism of Au/<i>n</i>-GaN Schottky Contact Modified Using a Copper Pthalocyanine (CuPc) Interlayer

“…GaN has established a place for itself in the field of solidstate devices, with applications ranging from light-emitting diodes 1) and visible-blind photodetectors 2) to high power Schottky diodes 3) and high electron mobility transistors. 4) Among them, Schottky devices such as ultraviolet photodetectors, solar-blind diodes and high electron mobility transistors have recently experienced spurts of further development.…”

Influence of premetallization surface treatment on the formation of Schottky Au-nGaN contacts

“…Additionally, its high work function ͑5.2 eV͒ means gold is an ideal choice for Schottky rectifiers on nGaN and for Ohmic contacts to pGaN. Au-GaN contact formation has been widely investigated [1][2][3][4][5][6][7] by current-voltage (I-V) and capacitance measurement techniques. These works report that gold does indeed form rectifying contacts on nGaN, with measured barrier heights ranging from 0.80 to 1.1 eV.…”

“…The Ohmic contact was provided by a large-area Au contact left on the sample during lithography. 2,14,15 The XPS spectra were acquired using a VG Microlab system attached to a custom-built evaporation chamber. The base pressure was 10 Ϫ10 mb and the Mg anode gave an energy resolution of 0.9 eV.…”