Normally-off field-effect transistor and its manufacturing method

Abstract

A normally-off field effect transistor and a preparation method thereof, the transistor comprising: a gallium nitride substrate (1); a gallium oxide epitaxial layer (2), which is formed on the gallium nitride substrate (1), and the two alternate The interface forms a gallium nitride / gallium oxide heterojunction interface; the aluminum nitride epitaxial layer (3) is formed on the gallium oxide epitaxial layer (2), and the interface between the two forms an aluminum nitride / gallium oxide heterojunction interface; A cap layer (4) formed on the aluminum nitride epitaxial layer (3). The transistor makes full use of the material properties of Group III nitride and gallium oxide, generates high-density polarized charges at the interface of aluminum nitride / gallium oxide, increases the concentration of two-dimensional electron gas, increases conductivity, and improves the electrical performance of field effect transistors. In terms of normally-off operation, p-type gallium nitride is used as the gate cap layer, so that the threshold voltage is not affected by the interface state, and the reliability of the field effect transistor is enhanced, and the resistivity under the channel is increased, reducing the drain leakage current and subthreshold swing.

Description

technical field [0001] The invention relates to the field of semiconductor devices, in particular to a normally-off field effect transistor and a preparation method thereof. Background technique [0002] Existing semiconductor normally-off field effect transistors are mainly realized by aluminum gallium nitride / gallium nitride (AlGaN / GaN)-based semiconductor materials. Since both AlGaN and GaN have a polarization effect, the AlGaN / GaN interface will generate polarized positive charges to attract electrons, forming a two-dimensional electron gas (2DEG), and transporting electrons through the 2DEG channel at the interface. [0003] The defects of this kind of transistor are as follows: First, the polarized charge of opposite polarity generated at the interface between AlGaN and GaN materials will reduce the net polarized charge density, resulting in a decrease in 2DEG concentration and conductivity, which limits device performance. Second, AlGaN / GaN-based normally-off field e...

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Problems solved by technology

[0003] The defects of this kind of transistor are: First, the polarized charges of opposite polarity generated at the interface between AlGaN and GaN materials will reduce the net polarized charge density, resulting in a decrease in 2DEG concentration and a decrease in conductivity, which limits device performance

Second, AlGaN / GaN-based normally-off field effect transistors use methods such as insulated gate field-effect transistor structures, cascode structures, and fluorine ion implantation to achieve normally-off operations, but the normally-off devices based on the above methods will be affected by the process. The interface state generated in or long-term use leads to a threshold voltage (V th ) is reduced, affecting the normal operation of the device

Third, when the device is in the off-state condition, when the drain-source voltage is large, the drain leakage current phenomenon is prone to occur, causing a large current in the device that should be turned off, which affects the normal operation of the device

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