MOCVD Growthof Algan/Ganheterostructures on 6 Inchsilicon
MOCVD Growthof AlGaN/GaNHeterostructures on 6 inchSilicon
Jie Su, Hongwei Li, Seungjae Lee, Balakrishnan Krishnan, Dong Lee, George Papasouliotis, and Ajit Paranjpe
Veeco MOCVD Operations, 394 Elizabeth Avenue, Somerset, NJ 08873, USA
Phone: (732) 560-5300 Email:
Key words: MOCVD, AlGaN/GaNheterostructure, HEMT, 2DEG
Due to the low cost and availability of Si substrateswith larger diameters (> 6 inch) compared with sapphire and SiC substrates, AlGaN/GaN based High Electron Mobility Transistors (HEMTs) on Si have emerged as a promising candidate for high frequency power amplification and high voltage power switching applications. With the growth challenges of heteroepitaxy of GaN on Si, device quality GaN and manufacturability have to be demonstrated for the potential mass production and broad applications of AlGaN HEMTs on Si.
Here we will reportthe growth of AlGaN/GaNheterostructures on 6 inch Si using a Veeco K465i production MOCVD system. The epitaxy process, GaN/AlGaN structural qualities and2DEG properties will be presented, showing the process repeatability and manufacturing feasibilities. The schematic of the AlGaN/GaNheterostructure is shown in Figure 1 (a). The growth does not require any pre-growth wafer conditioning. The Si wafer is first annealed at high temperature (>1000 C) under Hydrogen ambient, which is followed by the pre-flow of TMAl without the presence of ammonia. The buffer layers consist of a 150nm AlN nucleation layer and three step-graded AlxGa1-xN intermediate layers with x=0.75, 0.5, and 0.25. The thickness of the three AlxGa1-xN layers is 200 nm, 250 nm and 300nm, respectively. About 2-3 um GaN layer is grown on top of the AlGaN buffer layers with one optional stain-relieving AlN interlayer. The unintentionally doped Al0.25Ga0.75N barrier layer is grown without a GaN cap in order to inspect the AlGaN surface morphology. The surface morphology of the AlGaN is studied by AFM, and the electrical properties of the 2DEG are evaluated by Van der Pauw-Hall measurement.
For a 25nm Al0.25Ga0.75N barrier, the 2DEG mobility is > 1500 cm2/v.s without an AlN spacer, and mobility >2000 cm2/v.s with a 1nm AlN spacer at the AlGaN/GaN interface, shown in Figure 1 (b) and (c). The surface morphology of the AlGaN barrier without an AlN spacer is shown in Figure 2 (a)-(e). The AlGaN surface shows no micro-cracks and a step-flow feature comparable to the surface of the underlying GaN layer, indicating the pseudomorphic growth of AlGaN with less strain relaxation. Repeat runs (within 70 continuous runs without chamber opening) with the same AlGaN conditions show similar smooth surface and comparable 2DEG mobility above 1500 cm2/v.s at room temperature, as show in Figure 3.
Figure 1 Schematic and 2DEG performance of the AlGaN/GaNheterostructure
Figure 2 5mx5m AFM images of repeat runs of AlGaN/GaNheterostructure
Figure 3 2DEG performance of repeat runs of AlGaN/GaNheterostructure