High figure of merit extreme bandgap Al_0.87Ga_0.13N-Al_0.64Ga_0.36N heterostructures over bulk AlN substrates

Abstract

We report on high-quality n-Al0.87Ga0.13N-A0.64Ga0.36N heterostructures over single crystal AlN. For these pseudomorphic heterostructures, high resolution X-ray and X-ray Topographic analysis was used to establish a threading dislocation density of 7x103 cm-2. Using reverse composition graded n+-AlxGa1-xN contact layers, we obtained linear ohmic contacts with 4.3 Ω-mm specific resistance. A critical breakdown field > 11 MV/cm was also measured. In combination with the channel resistance of 2400 Ω/sq , these translate to a Baliga’s Figure of Merit (BFOM) of 2.27 GW/cm2. This, to the best of our knowledge is the highest reported value for extreme bandgap (EBG) AlGaN heterostructures.

Al0.64Ga0.36N channel MOSHFET on single crystal bulk AlN substrate

“…The reduced dislocations in such pseudomorphic epilayer structures, can in principle lead to significantly lower gatecurrents thereby promoting device stability. 15) In this work, we demonstrate a pseudomorphic Al 0.87 Ga 0.13 N/ Al 0.64 Ga 0.36 N metal-oxide-semiconductor HFETs (MOSHFET) on a single crystal bulk AlN substrate with linear ohmic contacts enabled by a reverse composition graded contact-making Al x Ga 1−x N layer, 16) and a thick dielectric cap layer to eliminate premature surface breakdown. These innovations enabled MOSHFET devices with on-state peak drain current (I DS ) density of 610 mAmm −1 (at +2 V gate bias), on-off ratio (∼10 7 ), and a three-terminal off-state breakdown field >3.7 MV cm −1 for a device with the gate-drain spacing L GD = 2.64 μm.…”

“…It was grown on a bulk AlN substrate with low-pressure metalorganic-chemical vapor deposition (LP-MOCVD) using a procedure described in our earlier report. 16) The structure consisted of a 260 nm homoepitaxial AlN layer followed by a 140 nm i-Al 0.87 Ga 0.13 N back-barrier, a 100 nm i-Al 0.64 Ga 0.36 N channel layer, and a 23 nm thick n-Al 0.87 Ga 0.13 N barrier layer. To facilitate ohmic contact formation, the structure was capped with a 30 nm thick highly Si-doped reverse-graded Al x Ga 1−x N (x = 0.87 → 0.40) layer.…”

“…From these, the contact resistances 4.3 Ωmm (∼7.7 × 10 −5 Ωcm 2 ) and 4.7 Ωmm (∼9.7 × 10 −5 Ωcm 2 ) and the sheet resistances of 2400 Ωsq −1 and 2282 Ωsq −1 were extracted for devices on single crystal bulk AlN and AlN/sapphire template, respectively. 16) The TLM results for the single crystal bulk AlN-based device are shown in Fig. 1(b).…”

“…1. (a) Schematic cross-section of high-Al Al 0.64 Ga 0.36 N channel MOSHFET for this study (b) TLM measurement results with W = 200 μm and contact spacings from 4 to 16 μm for single crystal AlN 16).…”