AlGaN/GaN Schottky Gate Fin-HEMT Fabricated on 8-inch Silicon (111) Substrate with Thin Buffer Layer Li-Cheng Chang 1 , Cheng-Jia Dai 1 , Ming Yang 1 , Yi-Hong Jiang 1 , and Chao-Hsin Wu 1,2 1 Graduate Institute of Electronics Engineering, National Taiwan University, Taipei, Taiwan 2 Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei, Taiwan Phone: +886-2-3366-3694 E-mail: chaohsinwu@ntu.edu.tw Abstract In this letter, we demonstrate the AlGaN/GaN Fin-HEMT on 8-inch Si (111) substrate with thin AlGaN buffer which is about 3 μm. This Fin-HEMT is charac- terized by the Schottky gate without any insulating die- lectric. This Schottky gate creates the depletion region on both sidewalls of the fin channel can further deplete the carrier. This sidewall assistant makes the device turns off earlier than planar device which is confirmed by the positive shift of the threshold voltage (V TH ). The minimum fin width is characterized by 100 nm and the corresponding V TH is -0.5 V which has 3.05 V shift from the planar device. 1. Introduction Owing to the superior material properties such as high breakdown field, low ON-resistance (R ON ), and high thermal stability, GaN-based high-electron-mobility transistors (HEMTs) have huge potential of the applications in power electronics [1-3]. In terms of material properties, Al- GaN/GaN heterojunction exhibits 2DEG inherently due to its unique properties of polarization but also results in nor- mally-ON operation. For the normally-ON, i. e., enhance- ment-mode (E-mode) device, it is more complicated for cir- cuit design and less output efficiency. In this paper, we uti- lize the fin-shaped channel to modulate the threshold volt- age (V TH ) toward positive value [4,5]. The gate metal in our Fin-HEMT is deposited directly on the AlGaN/GaN fin channel to form the Schottky contact on all sides of fin. It should be noted that the Schottky contact has wider deple- tion width than the metal-insulator-semiconductor contact. Therefore, once the fin becomes narrow enough, it is possi- ble to fully deplete 2DEG through the sidewall depletion region earlier than the top-gate control. This leads to the positive V TH movement and the switching mechanism is similar to the metal-semiconductor field-effect transistor. 2. Device Fabrication The epitaxial structure of AlGaN/GaN is grown by MOCVD and starts on 8 inch silicon wafer with a 300 nm AlN nucleation layer, ~3.2 μm graded AlGaN buffer, 2 μm undoped GaN layer, 30 nm undoped Al 0.3 Ga 0.7 N barrier, and 1 nm undoped GaN cap layer. The specific layer structure is shown in Fig. 1 (a). After the material growth, hall meas- urement is implemented form the center to the edge of wafer with 9 points. The results show that peak and average mo- bility is 1520 cm 2 /Vs and 1323 cm 2 /Vs, respectively which suggest that high uniformity of the epitaxy. The process flow and schematic diagram of device are shown in Fig. 1 (b) and the device is begun with fin for- mation. The minimum fin width (W fin ) here is 100 nm which defined by the electron-beam lithography and is etched by the Cl 2 /BCl 3 mixed plasma. The Ti/Al/Ni/Au deposition and rapid thermal annealing is then applied in sequence to form the S/D Ohmic contact. Finally, gate metal with Ni/Au is deposited to complete the device. It should be noted that gate metal is deposited directly on the fin channel to form the Schottky contact on all sides. Fig. 2 is the SEM image of the device with 100 nm W fin . The fin number of 100 nm W fin is 100 and thus we can defined the projective channel width is the production of W fin and fin number. 3. Results and Discussions The comparison of the transfer characteristics with dif- ferent W fin is shown in Fig. 3 (a). We can observe that the V TH of the fin device has significant shift toward positive value comparing to planar one. The V TH of device with W fin of 100 nm and gate length (L g ) of 2 μm is characterized by -0.7 V and the planar one is -3.75 V with the same L g and the gate width (W g ) is 60 μm. The V TH is defined by the current density of 100 μA/mm normalized by the projective (a) (b) Fig. 1. (a) Layer structure of the 8-inch AlGaN/GaN-on-Si. (b) Process flow and schematic diagram of our Fin-HEMT. It should be noted that gate metal is deposited directly on the fin channel. Fig. 2. SEM image of the Fin-HEMT with the minimum W fin of 100 nm. PS-6-06 Extended Abstracts of the 2017 International Conference on Solid State Devices and Materials, Sendai, 2017, pp833-834 - 833 -