Abstract
By employing a single AlGaN layer with low Al composition, high quality and uniformity AlGaN/GaN heterostructures have been successfully grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). The heterostructures exhibit a high electron mobility of 2150 cm2/Vs with an electron density of 9.3 × 1012 cm−2. The sheet resistance is 313 ± 4 Ω/◻ with ±1.3% variation. The high uniformity is attributed to the reduced wafer bow resulting from the balance of the compressive stress induced and consumed during the growth, and the thermal tensile stress induced during the cooling down process. By a combination of theoretical calculations and in situ wafer curvature measurements, we find that the compressive stress consumed by the dislocation relaxation (~1.2 GPa) is comparable to the value of the thermal tensile stress (~1.4 GPa) and we should pay more attention to it during growth of GaN on Si substrates. Our results demonstrate a promising approach to simplifying the growth processes of GaN-on-Si to reduce the wafer bow and lower the cost while maintaining high material quality.
Highlights
AlGaN/GaN heterostructures grown on Si substrates have attracted much attention for high power, high frequency, and high temperature applications[1,2,3,4]
The questions are: whether the first two step-graded AlGaN buffers are necessary for crack free GaN on Si substrate? Is it possible to get high quality GaN based materials on Si substrate using only a single AlGaN buffer layer?
In order to answer the above questions, we only keep the last AlGaN buffer layer with low Al composition in this work. By employing this low Al composition AlGaN layer as the stress-control layer, crack-free GaN buffer layers with a small wafer bow of 18 μm were obtained on 100 mm Si substrates
Summary
The GaN layers and AlGaN/GaN heterostructures used in this work were grown on 650 μm thick 100 mm p-type Si (111) substrates by metal-organic chemical vapor phase deposition (MOCVD) with close coupled showerhead 3 × 2 inch reactor (Aixtron CCS). An AlN buffer with a thickness of 270 nm was deposited at about 1100 °C followed by a single 330 nm thick AlGaN intermediate layer and a 2 μm-thick GaN layer. The AlGaN layer was grown at 1060 °C. The Al composition of the AlGaN interlayer is measured to be about 23% by high resolution X-ray diffraction (HR-XRD). All the layers were grown at a pressure of 100 mbar. Ohmic contacts were prepared by depositing Ti/Al/Ni/Au (20/150/35/100 nm) metal stacks followed by a rapid thermal annealing at 850 °C for 35 s under nitrogen atmosphere
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