▎ 摘　　要

NOVELTY - The device has a silicon carbide substrate layer (1), an aluminum nitride nucleating layer (2), a relaxation layer A (3), a relaxation layer B (4), an aluminum gallium nitrogen buffer layer (5), a gallium nitride channel (6), and an aluminum gallium nitrogen barrier layer (7) sequentially stacked from bottom to top. A source electrode (8) and a drain electrode (9) are provided at both ends of the surface of the aluminum gallium nitrogen barrier layer. The surface of the aluminum gallium nitrogen barrier layer is located between the source electrode and the drain electrode is provided with an isolated insulating layer A and an insulating layer B. The insulating layer A, the insulating layer C and the gate layer B form the main gate and the insulating layer B. The sub-gate composed of gate layer A is connected through the graphene film electrode to form a series-parallel mixed double high frequency characteristics high electron mobility transistor (HEMTs) integrated structure. USE - The device is useful in mobile phone and satellite of TV and radar. Can also be used in high electron mobility transistor (HEMT). ADVANTAGE - The method improves the threshold voltage and improve applicability of the device, increases width of the integrated device, and realizes function of control capacitance, and enhances frequency characteristics of a device, and increases the threshold voltage of the normally closed gallium nitride integrated device to 3.7V. DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for a method for preparing normally-closed gallium nitride integrated device with a large threshold voltage. DESCRIPTION OF DRAWING(S) - The drawing shows a structural schematic diagram of the normally-closed gallium nitride integrated device of large threshold voltage. 1Silicon carbide substrate layer 2Aluminum nitride nucleating layer 3Relaxation layer A 4Relaxation layer B 5Aluminum gallium nitrogen buffer layer 6Gallium nitride channel 7Aluminum gallium nitrogen barrier layer 8Source electrode 9Drain electrode 10Insulating layer 11Insulating layer b 12Silicon dioxide layer 13Gate layer 14Graphene film electrode 15Insulating layer c 16Gate layer b 17Aluminum electrode layer