Normally-off field effect transistor and preparation method thereof

Abstract

The invention discloses a normally-off field effect transistor and a preparation method thereof. The transistor comprises: a gallium nitride substrate (1); a gallium oxide epitaxial layer (2) formed on the gallium nitride substrate (1), wherein a gallium nitride / gallium oxide heterojunction interface is formed at the interface of the gallium oxide epitaxial layer and the gallium nitride substrate;an aluminum nitride epitaxial layer (3) formed on the gallium oxide epitaxial layer (2), wherein an aluminum nitride / gallium oxide heterojunction interface is formed at the interface of the aluminumnitride epitaxial layer and the gallium oxide epitaxial layer; and a cap layer (4) formed on the aluminum nitride epitaxial layer (3). According to the transistor, the material characteristics of III-nitride and gallium oxide are fully utilized, and high-density polarized charges are generated at an aluminum nitride / gallium oxide interface; in the aspect of achieving normally-off operation, p-typegallium nitride is adopted as a gate cap layer, so that the threshold voltage is not influenced by an interface state, the reliability of the field effect transistor is enhanced, the resistivity below a channel is improved, and the drain leakage current and the sub-threshold swing are reduced.

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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