CN108807500B

CN108807500B - An Enhancement Mode High Electron Mobility Transistor with High Threshold Voltage

Info

Publication number: CN108807500B
Application number: CN201810540129.XA
Authority: CN
Inventors: 张�雄; 陈虎; 吴自力; 崔一平
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2018-05-30
Filing date: 2018-05-30
Publication date: 2021-08-03
Anticipated expiration: 2038-05-30
Also published as: CN108807500A

Abstract

The invention discloses an enhanced high-electron-mobility transistor with high threshold voltage, which comprises a substrate, a buffer layer, a non-doped GaN layer, an n-type AlGaN layer and a passivation layer which are sequentially arranged from bottom to top, wherein a source electrode and a drain electrode are respectively arranged at two ends of the n-type AlGaN layer and are in contact with the non-doped GaN layer, and a grid electrode is arranged on the n-type AlGaN layer; the n-type AlGaN layer is composed of a nitrogen polarity AlGaN layer and a metal polarity AlGaN layer. According to the invention, a nitrogen polarity AlGaN layer with a polarity different from that of the traditional metal and an AlGaN/GaN heterojunction energy band structure formed by the GaN layer with the polarity of the metal are introduced, so that higher threshold voltage is realized.

Description

Enhanced high electron mobility transistor with high threshold voltage

Technical Field

The invention belongs to the technical field of semiconductor devices, and particularly relates to an enhanced high electron mobility transistor with high threshold voltage.

Background

The GaN-based High Electron Mobility Transistor (HEMT) is a heterojunction field effect transistor, forms a conductive channel by utilizing two-dimensional electron gas with quantum effect in a heterojunction, has the advantages of wide forbidden band, high saturated electron mobility, high breakdown electric field, high thermal conductivity and the like, and is widely applied to the field of high-frequency, high-power, high-temperature and high-radiation devices.

However, as shown in fig. 1, it is the two-dimensional electron gas with high concentration at the AlGaN/GaN heterojunction interface, so that the HEMT device prepared therefrom is also necessarily a depletion device while having high saturation electron mobility, i.e. when no bias voltage is applied, the source and drain of the device are in on state, resulting in reduced system safety and increased device loss.

In order to improve the electrical performance of HEMT devices and the compatibility of HEMT devices with integrated circuits, in the prior art, depletion mode HEMTs are generally converted into enhancement mode HEMTs by adopting schemes such as a fluorine ion implantation method, a thin barrier layer, a recessed gate structure and the like. But the threshold voltage which can be realized by the fluorine ion implantation method is smaller, and the implantation damage can be caused to the surface of the device; the thin barrier layer technology can cause the on-resistance of the source and the drain of the HEMT device to be overlarge and the saturation current of the device to be smaller; and the etching process adopted by the concave gate structure is difficult to control and has poor repeatability. In addition, in order to realize the normally-off characteristic of the enhancement mode HEMT device prepared by the above prior art, a method of increasing the barrier height of the AlGaN layer or reducing the spontaneous polarization electric field at the AlGaN/GaN heterojunction interface is adopted. As shown in fig. 2, it can be seen from the structure diagram of the energy band of the AlGaN/GaN heterojunction in the enhancement mode HEMT device prepared in the prior art that the threshold voltage realized by the device is relatively small because the conduction band energy level near such heterojunction is closer to the fermi level.

Reference documents:

1.Kuzuhara M, Asubar J T, Tokuda H. AlGaN/GaN high-electron-mobility transistor technology for high-voltage and low-on-resistance operation[J]. Jpn.j.appl.phys, 2016, 55(7):070101。

2.Meneghesso G, Meneghini M, Rossetto I, et al. Reliability and parasitic issues in GaN-based power HEMTs: a review[J]. Semiconductor Science Technology, 2016, 31(9):093004。

disclosure of Invention

The purpose of the invention is as follows: aiming at the problem that the threshold voltage of the enhancement type HEMT device prepared by the prior art is lower, the invention provides a novel enhancement type high electron mobility transistor with high threshold voltage.

The technical scheme is as follows: in order to achieve the purpose, the invention adopts the following technical scheme:

an enhanced high-electron-mobility transistor with high threshold voltage comprises a substrate, a buffer layer, a non-doped GaN layer, an n-type AlGaN layer and a passivation layer which are sequentially arranged from bottom to top, wherein a source electrode and a drain electrode are respectively arranged at two ends of the n-type AlGaN layer and are in contact with the non-doped GaN layer, and a grid electrode is arranged on the n-type AlGaN layer; the n-type AlGaN layer is composed of a nitrogen polarity AlGaN layer and a metal polarity AlGaN layer.

Preferably, the nitrogen polarity AlGaN layer is positioned right below the grid, has the same width as the grid and is 10-3000 nm; the thickness of the nitrogen polarity AlGaN layer is the same as that of the metal polarity AlGaN layer and is 50-5000 nm.

Preferably, the buffer layer and the non-doped GaN layer are both metal polarity, the thickness of the buffer layer is 20-2000nm, and the thickness of the non-doped GaN layer is 50-5000 nm.

Preferably, the n-type AlGaN layer may be doped with Si, S, Se, or Te to have an electron concentration of 1 × 10¹⁵cm^-3-1×10²⁰ cm^-3。

Preferably, the substrate is one of sapphire, silicon carbide, silicon, zinc oxide, gallium nitride or aluminum nitride.

Preferably, the source and the drain are in ohmic contact with the undoped GaN layer, and the gate is in schottky contact with the n-type AlGaN layer; the electrode material adopted by the source electrode, the drain electrode and the grid electrode is an alloy formed by one or more of metal Ni, Al, In, Au or Ti.

Preferably, the passivation layer material is SiO₂Or silicon nitride with a thickness of 10-1000 nm.

Has the advantages that: according to the enhancement type high electron mobility transistor with the high threshold voltage, a layer of high-density negatively charged surface charges can be generated at an AlGaN/GaN heterojunction interface by introducing the nitrogen polarity AlGaN layer with the spontaneous polarization electric field direction opposite to that of the gallium polarity GaN layer arranged below the nitrogen polarity AlGaN layer. The built-in electric field generated by the surface charges can modulate a heterojunction energy band structure, so that a conduction band energy level originally below a Fermi energy level at an AlGaN/GaN heterojunction interface is bent upwards, the conduction band energy level of a channel below a grid is effectively improved, two-dimensional electron gas in the channel is rapidly exhausted, and the normally-off characteristic of an HEMT device can be realized. According to the invention, the nitrogen polarity AlGaN layer different from the traditional metal polarity is introduced, so that not only can the HEMT device be converted from a depletion type to an enhancement type, but also the conduction band energy level of the channel heterojunction below the grid can be obviously improved to be higher than the Fermi energy level, therefore, the threshold voltage of the HEMT device can be effectively improved, the anti-interference capability of the device is increased, and the static power consumption of the device is reduced, which has important significance for the large-scale application of the HEMT device in the field of high-power electronics.

Drawings

Fig. 1 is a schematic cross-sectional structure of a common depletion mode HEMT prepared in the prior art, wherein the numerical meaning is: the GaN-based light-emitting diode comprises a substrate (201), a buffer layer (202), a non-doped GaN layer (203), an n-type AlGaN layer (204) and a passivation layer (205), a source electrode (206) and a drain electrode (207) which are respectively arranged at two ends of the n-type AlGaN layer (204) and are in contact with the non-doped GaN layer (203), a grid electrode (208) arranged on the n-type AlGaN layer (204) and two-dimensional electron gas (209) formed at an AlGaN/GaN heterojunction interface.

Fig. 2 is a diagram showing the band structure of AlGaN/GaN heterojunction in an enhancement type HEMT device manufactured in the prior art.

Fig. 3 is a schematic cross-sectional structure diagram of an enhancement HEMT with a high threshold voltage provided in example 1, wherein the numerals mean: the GaN-based light-emitting diode comprises a substrate (101), a buffer layer (102), a non-doped GaN layer (103), an n-type AlGaN layer (104) and a passivation layer (105), a source electrode (106) and a drain electrode (107) which are respectively arranged at two ends of the n-type AlGaN layer (104) and are in contact with the non-doped GaN layer (103), a grid electrode (108) arranged on the n-type AlGaN layer (104) and two-dimensional electron gas (109) formed at an AlGaN/GaN heterojunction interface; wherein the n-type AlGaN layer (1041) directly under the gate (108) has a nitrogen polarity, and the remaining n-type AlGaN layers (1042) have a metal polarity.

Fig. 4 is a structure diagram of an AlGaN/GaN heterojunction energy band including a nitrogen-polar AlGaN layer provided in example 1.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the embodiments described herein are only intended to specifically explain the present invention and are not intended to limit the scope of the claims of the present invention.

Example 1

Fig. 3 is an enhancement HEMT with a high threshold voltage, which is provided by the present invention, and the enhancement HEMT is sequentially provided with a sapphire substrate (101), an AlN buffer layer (102), an undoped GaN layer (103), an n-type AlGaN layer (104), and a silicon nitride passivation layer (105) from bottom to top, wherein the n-type AlGaN layer (104) is composed of a nitrogen polarity AlGaN layer (1041) and a metal polarity AlGaN layer (1042). A source (106) and a drain (107) are respectively arranged at two ends of the n-type AlGaN layer (104) and are in contact with the non-doped GaN layer (103), and a gate (108) is arranged on the n-type AlGaN layer (104).

The nitrogen polarity AlGaN layer (1041) is located right below the grid (108), the width of the nitrogen polarity AlGaN layer is the same as that of the grid (108) and is 1000nm, and the thickness of the nitrogen polarity AlGaN layer is the same as that of the metal polarity AlGaN layer (1042) and is 200 nm.

The introduction of the nitrogen polarity AlGaN layer (1041) can be realized by the following steps: 1. depositing a patterned layer of Al on the undoped GaN layer (103) using atomic layer deposition techniques₂O₃A film; 2. for deposited Al₂O₃Performing nitridation treatment on the film; 3. by metal organic chemical vapor deposition on Al₂O₃An n-type AlGaN layer (1041) of nitrogen polarity is epitaxially grown on the thin film without being coated with Al₂O₃A metal polarity n-type AlGaN layer (1042) is grown on the film-covered GaN layer (103).

The AlN buffer layer (102) and the non-doped GaN layer (103) are both metal-polar, and the thicknesses of the AlN buffer layer and the non-doped GaN layer are respectively 100nm and 300 nm.

The n-type AlGaN layer (104) may utilize SiH during epitaxial growth₄Doping to obtain doped crystal with electron concentration of 1 × 10¹⁸ cm^-3And the Al component is 0.3.

The sapphire substrate (101) is a polar (0001) C-plane sapphire substrate.

The contact formed by the source electrode (106) and the drain electrode (107) and the non-doped GaN layer (103) is ohmic contact, the contact formed by the grid electrode (108) and the n-type AlGaN layer (104) is Schottky contact, and the electrode materials are Ni/Au alloy.

The thickness of the silicon nitride passivation layer (105) is 300 nm.

It is important to explain that the core part of the enhancement mode HEMT with high threshold voltage of the invention is an AlGaN/GaN heterojunction composed of an n-type nitrogen polarity AlGaN layer (1041) and a metal polarity non-doped GaN layer (103). This part is the key to the present invention to enable significant bending and lifting of the conduction band energy level at the AlGaN/GaN heterojunction interface, which is originally below the fermi level, upwards. The method has the main effects of quickly depleting two-dimensional electron gas in a channel and greatly increasing the conduction band energy level at the heterojunction to be above the Fermi energy level, so that the threshold voltage of the enhancement type HEMT device can be obviously increased.

The above description is only a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above embodiment, but equivalent modifications or changes made by those skilled in the art according to the present disclosure should be included in the scope of the present invention as set forth in the appended claims.

Claims

1. An enhancement mode high electron mobility transistor with high threshold voltage, characterized in that it comprises a substrate (101), a buffer layer (102), an undoped GaN layer (103), a substrate (101), a buffer layer (102), an undoped GaN layer (103), The n-type AlGaN layer (104) and the passivation layer (105), the source electrode (106) and the drain electrode (107) are respectively disposed on both ends of the n-type AlGaN layer (104) and form contact with the undoped GaN layer (103). , the gate (108) is arranged on the n-type AlGaN layer (104);

The n-type AlGaN layer (104) is composed of a nitrogen polar AlGaN layer (1041) and a metal polar AlGaN layer (1042);

The nitrogen-polar AlGaN layer (1041) is located directly under the gate (108), and has the same width as the gate (108), both being 10-3000 nm; the nitrogen-polar AlGaN layer (1041) has a thickness equal to that of the metal-polar AlGaN layer (1042) are the same, both are 50-5000 nm.

2. The enhancement mode high electron mobility transistor with high threshold voltage according to claim 1, wherein the buffer layer (102) and the undoped GaN layer (103) are both metal polarities, and the buffer layer (102) has a thickness of 20-2000 nm, and the undoped GaN layer (103) has a thickness of 50-5000 nm.

3. The enhancement mode high electron mobility transistor with high threshold voltage according to claim 1, wherein the n-type AlGaN layer (104) can be doped with Si, S, Se or Te, and the doping The back electron concentration is 1×10 ¹⁵ cm ⁻³ to 1×10 ²⁰ cm ⁻³ .

4. The enhancement mode high electron mobility transistor with high threshold voltage according to claim 1, wherein the substrate (101) is sapphire, silicon carbide, silicon, zinc oxide, gallium nitride or nitride A type of aluminum.

5. The enhancement mode high electron mobility transistor with high threshold voltage according to claim 1, characterized in that: the source electrode (106) and the drain electrode (107) are formed with the undoped GaN layer (103). The contact is an ohmic contact, and the contact formed between the gate electrode (108) and the n-type AlGaN layer (104) is a Schottky contact; the electrode materials used for the source electrode (106), the drain electrode (107) and the gate electrode (108) are: An alloy composed of one or more of metals Ni, Al, In, Au or Ti.

6 . The enhancement mode high electron mobility transistor with high threshold voltage according to claim 1 , wherein the passivation layer ( 105 ) is made of SiO ₂ or silicon nitride with a thickness of 10-1000 nm. 7 .