(Invited) High-Power AlGaN/GaN Heterostructure Field-Effect Transistors on 200mm Si Substrates

GaN-based electronic devices have established their niches for both high power switching application and high frequency operation due to their wide-bandgap, excellent transport properties, and high critical electric field, which cannot be achieved by the Si-based electronics.  Especially, AlGaN/GaN heterostructure field-effect transistors (HFETs) have shown great promises in a wide range of applications, such as highly efficient power amplifiers for mobile phone base-stations, commercial and military radar/satellite communications, power rectifiers with unprecedentedly low loses, and various circuits in industrial equipment and electric/hybrid vehicles.  Among all suitable substrates for III-nitride crystal growth, such as sapphire, SiC, silicon, and GaN bulk, Si substrates have the advantage of the lowest cost, and are available in diameters of beyond 300 mm, although the substrate size available for nitride growth is limited by suitable deposition equipment and the requirement of (111) substrate orientation; they are also easily compatible to be fabricated in well-developed Si–based foundry.  To realize the GaN performance in a cost-down platform and to continue using well-developed device fabrication technologies easily scalable to 200 mm and beyond in modern semiconductor industry, the integration of GaN-based electronics with Si platform is not only extremely emergent but also a win-win investment.

Despite the tremendous promise and progress in GaN-on-Si technology [1], challenges associated with epitaxial growth of large diameter wafers remain.  In this work, we will summarize current status of AlGaN/GaN HFET growth on (111) on-axis silicon substrates varying from 100 to 200 mm in diameter by using metal–organic chemical vapor deposition (MOCVD).  All substrates used for this study were per SEMI standard thickness.  The total thickness of the HFET epilayers was in the range of 2 – 4.5 µm.  The material characterization data will be compared between these III-nitride crystal growths, such as the (002) and (102) x-ray rocking curves, the 2DEG mobility and charge density by Hall effect measurement, etc.  The devices analyzed in this study were fabricated using our standard device fabrication technology for AlGaN/GaN HFETs on Si.  Ti/Al/Ni/Au multilayer was first deposited and annealed at 850°C in a nitrogen environment to form an Ohmic contact.  Multiple doses and energies of nitrogen ion implantation were used for the device isolation and to maintain a planar geometry in the fabricated device to further reduce parasitic leakage current.  Ni/Au based Schottky gate metallization was defined by using optical lithography followed by a standard lift-off process of the e-beam deposited metals.  The gate dimension was 2 µm × 100 µm.  The distances of gate-to-source (L_gs) was fixed at 2 µm while the gate-to-drain distance (L_gd) varied from 2 µm to 10 µm.  The isolation characteristics were collected between two 250 µm × 150 µm Ohmic metal pads with 5 µm spacing.

Typical DC characteristics will be examined on the similar epitaxial structures grown on 100, 150 and 200 mm Si substrates and also compared between different epitaxial structures on 200 mm Si substrates.  For high voltage operation, the two-terminal isolation blocking voltage/leakage, as well as three-terminal off-state breakdown voltage and off-state drain leakage current for AlGaN/GaN HFETs on 200 mm silicon substrates with different thickness of the multi-buffer layers, based on (Al,Ga)N materials, will be discussed.  In order to suppress the off-state drain leakage current and improve the off-state breakdown voltage, a highly-resistive blocking buffer layer is needed, and therefore the intentional dopant [2], carbon, is utilized in the multi-buffer layers in this work.  As shown in the figure below, the isolation blocking voltage is demonstrated to increase up to 720V at 1µA/mm on 5µm-spacing isolation pads with increasing the thickness of the total epitaxial layers up to 4.5 µm and the isolation leakage current is as low as about 5 nA/mm.  Based on the insulating multi-buffer layers, high off-state breakdown voltage over 1000 V and low leakage current of 5×10^-8A are achieved with AlGaN/GaN heterostructures on 200 mm Si substrates.

1.  H. F. Liu, S. B. Dolmanan, L. Zhang, S. J. Chua, D. Z. Chi, M. Heuken, and S. Tripathy, Journal of Applied Physics 113, pp. 023510 (2013).

2. J. B. Webb, H. Tang, S. Rolfe, and J. A. Bardwell, Applied Physics Letters 75, 953-955 (1999).