CN115207116A - A gallium oxide transistor and a polarization control method for two-dimensional electron gas concentration - Google Patents

Abstract

The invention discloses a gallium oxide transistor and a polarization control method for two-dimensional electron gas concentration thereof. The transistor structure for polarization control of two-dimensional electron gas concentration is, from bottom to top, a substrate, an ε-phase gallium oxide, and an ε-phase respectively. GaAlO and top gate and source drain electrodes. ε-phase gallium oxide has a large spontaneous polarization and is considered to be a ferroelectric material, forming a two-dimensional electron gas at the interface of ε-phase gallium-aluminum oxide/ε-phase gallium oxide heterostructure. The present application utilizes the gate electrode and the substrate to apply a vertical electric field to the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure under the gate to change its polarization direction, and then remove the vertical electric field to realize the heterojunction interface under the gate The two-dimensional electron gas is exhausted. The advantage is that the state of the 2DEG at the heterojunction interface can be maintained after polarization regulation, which provides a new way to realize normally-off enhancement mode low-power transistors. The normally-off and normally-on types of gallium oxide devices can be switched on demand, and the device type can be flexibly adjusted.

Description

A gallium oxide transistor and a polarization control method for two-dimensional electron gas concentration

technical field

The invention relates to a gallium oxide transistor and a polarization control method for the concentration of two-dimensional electron gas.

Background technique

Gallium oxide Ga ₂ O ₃ is a new type of ultra-wide bandgap semiconductor material, and its crystal phases usually include α, β, γ, δ, and ε, among which the β phase is the most thermodynamically stable. β-Ga ₂ O ₃ is an emerging ultra-wide bandgap semiconductor material with excellent characteristics such as ultra-wide band gap of 4.8eV, ultra-high theoretical breakdown electric field of 8MV/cm, and ultra-high low loss index Baliga figure of merit. As a next-generation high-power device material, it has attracted more and more attention. However, the current mobility of gallium oxide is low, about 120-200 cm ² /(V·s), which limits its application to a certain extent. In the prior art, the generation of two-dimensional electron gas 2DEG through modulation doping of β-Ga ₂ O ₃ /β-(Al _x Ga _1-x ) ₂ O ₃ heterostructure is expected to improve mobility, but this modulation doping The impurity method has limited mobility improvement due to the effect of impurity scattering, and the preparation method is also relatively complicated.

At present, the mainstream high mobility transistor HEMTs are AlGaN/GaN system HEMTs, such as CN111799326A, CN113066863A and so on. In practical applications, normally-off operation is usually required to achieve low power consumption, such as CN110190116A. There are many ways to realize enhancement mode devices in AlGaN/GaN HEMT devices, such as releasing polarization stress by grooving the AlGaN layer under the gate, introducing p-type GaN gate, and depletion by doping F ions in the AlGaN layer under the gate, etc. Wait. The trench gate technology, the P-GaN cap layer and the F doping method have the disadvantages of damaging the channel or affecting the gate voltage regulation capability.

ε-phase gallium oxide ε-Ga ₂ O ₃ is considered to be a ferroelectric material and has a larger spontaneous polarization (P _SP about 0.23C/m ² ) than existing III-nitride semiconductors, and is expected to be Construction of heterostructures to obtain high concentrations of 2DEG. ε-Ga ₂ O ₃ can obtain 2DEG with a high concentration of 10 ¹⁴ cm ^-2 without modulation doping, which is an order of magnitude larger than the existing AlGaN/GaN heterostructure system. Although ε-Ga ₂ O ₃ can obtain a high concentration of 2DEG, it requires a larger negative gate voltage to turn off, which will bring extra power consumption in practical applications, so it is very important to realize normally-off transistor devices.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a gallium oxide transistor and a polarization control method for the concentration of two-dimensional electron gas, so as to solve the above-mentioned problems in the prior art.

The polarization regulation method of the two-dimensional electron gas concentration of the gallium oxide transistor described in the present invention utilizes the gate electrode and the substrate to apply a vertical electric field to the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure under the gate to change its polarity direction, and then remove the vertical electric field;

In the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure, a two-dimensional electron gas is formed at the interface of the ε-AlGaO ₃ layer and the ε-Ga ₂ O ₃ layer.

When the polarization directions of the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructures all point upward to the surface, a vertical electric field directed from the gate to the substrate is applied to change the polarization direction of the heterostructure under the gate. In order to point downward to the substrate, the two-dimensional electron gas at the interface of the heterojunction under the gate is in a depleted state.

When the polarization directions of the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructures under the gate all point downward to the substrate, a vertical electric field directed from the substrate to the gate is applied, so that the polarities of the heterostructures under the gate are At this time, the heterojunction interface under the gate gathers a high concentration of two-dimensional electron gas again.

The gallium oxide transistor described in the present invention comprises an ε-AlGaO ₃ layer, an ε-Ga ₂ O ₃ layer and a conductive substrate stacked in sequence; the ε-AlGaO ₃ layer and the ε-Ga ₂ O ₃ layer constitute ε -AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure, the interface of which forms a two-dimensional electron gas;

The drain electrode is arranged to extend through the ε-AlGaO ₃ layer to the ε-Ga ₂ O ₃ layer, and the drain electrode forms an ohmic contact with the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure;

The source electrode is arranged to extend through the ε-AlGaO ₃ layer to the ε-Ga ₂ O ₃ layer, and the source electrode forms an ohmic contact with the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure;

A gate electrode is also arranged between the source electrode and the drain electrode, and the gate electrode forms a Schottky contact with the upper surface of the ε-AlGaO ₃ layer;

The gate and the conductive substrate are used for external vertical electric field.

The thickness of the ε-AlGaO ₃ layer is 5 nm to 30 nm.

The thickness of the ε-Ga ₂ O ₃ layer is 200 nm to 1000 nm.

The ε-AlGaO ₃ has spontaneous polarization along the c-axis direction; the lattice constant can be selected as

The ε-Ga ₂ O ₃ has spontaneous polarization along the c-axis direction; the lattice constant can be selected as

The gallium oxide transistor and the polarization control method for the two-dimensional electron gas concentration of the present invention have the advantages that the state of the 2DEG at the interface of the heterojunction can be maintained after the polarization control, which provides a method for realizing normally-off and low power consumption transistors. new way. The normally-off and normally-on types of gallium oxide devices can also be switched on demand, and the device type can be flexibly adjusted.

Description of drawings

FIG. 1 is a schematic structural diagram of a gallium oxide transistor according to the present invention.

FIG. 2 is a schematic diagram of 2DEG distribution and polarization direction when a gallium oxide transistor according to the present invention is in depletion mode.

FIG. 3 is an energy band curve and a 2DEG concentration distribution curve diagram when a gallium oxide transistor according to the present invention is in a depletion mode.

FIG. 4 is a simulation curve diagram of the transfer characteristic of a gallium oxide transistor according to the present invention when it is in a depletion mode.

FIG. 5 is a circuit diagram of the polarization control method of the present invention.

FIG. 6 is a schematic diagram of the polarization regulation method of the present invention.

FIG. 7 is an energy band curve diagram when a gallium oxide transistor according to the present invention is an enhancement mode.

FIG. 8 is an energy band curve and a 2DEG concentration distribution curve diagram of a gallium oxide transistor according to the present invention when it is an enhancement mode and the bias is 1.2V.

FIG. 9 is a simulation curve diagram of transfer characteristics of a gallium oxide transistor according to the present invention when it is an enhancement mode.

Reference number:

1-conductive substrate, 2-ε- _Ga2O3 layer, ₃ -ε- _AlGaO3 layer, 4-drain, 5-gate, 6-source;

P _SP - spontaneous polarization, P _PZ - piezoelectric polarization.

Detailed ways

As shown in FIG. 1 , a gallium oxide transistor according to the present invention includes an ε-AlGaO ₃ layer, an ε-Ga ₂ O ₃ layer and a conductive substrate stacked in sequence. The ε-AlGaO ₃ layer and the ε-Ga ₂ O ₃ layer are epitaxially grown to form a ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure, and the interface produces 2DEG. A gate electrode is laid on the upper surface of the ε-AlGaO ₃ layer, and two ends of the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure are respectively provided with a drain electrode and a source electrode penetrating the ε-AlGaO ₃ layer.

In this embodiment, the conductive substrate can be selected from hexagonal Si, SiC or GaN material, and can also be replaced by a metal layer with high work function, such as Pt metal. Its function is to change its polarization direction by applying a vertical electric field to the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure under the gate in cooperation with the gate.

The thickness of the ε-Ga ₂ O ₃ layer is 200 nm to 1000 nm. ε-Ga ₂ O ₃ is a polar semiconductor material with spontaneous polarization P _SP ~0.23C/m ² along the c-axis direction. On the other hand ε-Ga ₂ O ₃ is also a ferroelectric material, which indicates that the spontaneous polarization direction of ε-Ga ₂ O ₃ can be changed under the action of an external electric field.

The thickness of the ε-AlGaO ₃ layer is 5 nm to 30 nm. Similar to ε-Ga ₂ O ₃ , ε-AlGaO ₃ is also a ferroelectric semiconductor with a spontaneous polarization P _SP ~0.13C/m ² along the c-axis direction, and its polarization direction can also be affected by an external electric field. changes happened.

The drain electrode and the source electrode pass through the ε-AlGaO ₃ layer and are deposited on the upper surface of the ε-Ga ₂ O ₃ layer to form ohmic contact with the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure to reduce the channel The series resistance between the channel and the electrode increases the device current. The gate is grown on the upper surface of the ε-AlGaO ₃ layer and forms a Schottky contact with the ε-AlGaO ₃ layer. The drain electrode, the source electrode and the gate electrode can all be made of metal materials, such as aluminum, gold, and platinum, and the specific selection is irrelevant to the concept of the present invention. A silicon nitride insulating layer is formed between the drain, source and gate to prevent leakage and breakdown between electrodes.

和

同属正交晶系。The ε-AlGaO ₃ layer and the ε-Ga ₂ O ₃ layer have strong spontaneous polarization, and at the same time produce a large piezoelectric polarization under epitaxial stress, the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure interface The polarization charge density is much higher than that of the AlGaN/GaN heterostructure. In the embodiment of the present invention, the lattice constants of the ε-AlGaO ₃ layer and the ε-Ga ₂ O ₃ layer can be respectively set as

and

belong to the orthorhombic system.

After epitaxial growth, the polarization direction of the original state is shown in Fig. 2. Both the position under the gate and the position outside the gate point upward to the surface, and there are residual polarized positive charges at the interface. The polarized positive charge can attract the electrons in the body region and make them gather at the interface to form a high-density 2DEG. At this time, the device is a depletion-type device. The energy band diagram and interface 2DEG concentration distribution of the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure are shown in Fig. 3 . The ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure interface forms a two-dimensional electron gas of 1×10 ²⁰ cm ^-2 , forming a high-quality conductive channel. Fig. 4 shows the transfer characteristic curve of the depletion-type field effect transistor obtained by the simulation calculation. After the device is turned on, the device operating current is 0.93A/mm, the maximum transconductance is 820mS/mm, and the turn-off voltage is about -2V.

If a normally-on depletion-mode device needs to be regulated into a normally-off enhancement-mode device, or vice versa, it is only necessary to add a vertical electric field of a certain strength between the gate and the conductive substrate. And obviously different from the prior art, the vertical electric field can be completely removed after the regulation is completed, and the regulation effect can be permanently maintained without retaining the external voltage. The circuit for vertical electric field application is shown in Figure 5.

Take the normally open depletion mode device as an example of a normally closed enhancement mode device: the gate is connected to the positive electrode of the power supply, and the conductive substrate is connected to the negative electrode of the power supply. After the vertical electric field is applied, the polarization direction is shown in Figure 6, and the polarization direction is reversed at the position below the gate, and the polarization direction points downward to the substrate. There are residual polarized negative charges at the interface, and the polarized negative charges repel electrons. After the vertical electric field is removed, the 2DEG in the channel under the gate is still in a depleted state at zero bias, and the device is in an off state at this time.

After the gate voltage of +1.2V is applied when the device is working, the energy band shifts down and induces 2DEG to realize the conduction of the device. As shown in Fig. 8, the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure interface under the gate forms a two-dimensional electron gas of 3.6×10 ¹⁸ cm ^-2 , which restores the conduction channel well. Fig. 9 shows the transfer characteristic curve of the enhancement mode field effect transistor obtained by the simulation calculation. The turn-on voltage of the device is about 0.5V, the operating current of the device after turning on is close to 0.89A/mm, and the maximum transconductance is 890mS/mm.

If the normally-off enhancement-mode device needs to be regulated into a normally-on depletion-mode device, it is only necessary to apply the reversed vertical electric field again to restore the state shown in Figure 2. Similarly, the applied vertical electric field can be removed after the regulation is completed.

For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims (8)

1. a kind of polarization control method of two-dimensional electron gas concentration of gallium oxide transistor, it is characterized in that, utilize gate electrode and substrate to under gate ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure to apply vertical electric field to change its polarization direction, and then remove the vertical electric field; In the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure, two-dimensional electron gas can be formed at the interface. 2 . The polarization control method of the two-dimensional electron gas concentration of a gallium oxide transistor according to claim 1 , wherein when the polarization directions of the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure are both When pointing upwards to the surface, a vertical electric field is applied from the gate to the substrate, causing the polarization direction of the heterostructure under the gate to be directed downwards to the substrate. 3. The polarization control method of the two-dimensional electron gas concentration of a gallium oxide transistor according to claim 1, wherein when the polarization of the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure under the gate When the directions are all pointing downward to the substrate, a vertical electric field is applied from the substrate to the gate, so that the polarization direction of the heterostructure under the gate is changed to point upward to the surface. 4. a gallium oxide transistor, is characterized in that, comprises successively stacked ε-AlGaO ₃ layers, ε-Ga ₂ O ₃ layers and conductive substrate; described ε-AlGaO ₃ layers and ε-Ga ₂ O ₃ layers It is composed of ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure, and its interface forms a two-dimensional electron gas; The drain electrode is arranged to extend through the ε-AlGaO ₃ layer to the ε-Ga ₂ O ₃ layer, and the drain electrode forms an ohmic contact with the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure; The source electrode is arranged to extend through the ε-AlGaO ₃ layer to the ε-Ga ₂ O ₃ layer, and the source electrode forms an ohmic contact with the ε-AlGaO ₃ /ε-Ga ₂ O ₃ heterostructure; A gate electrode is also arranged between the source electrode and the drain electrode, and the gate electrode forms a Schottky contact with the upper surface of the ε-AlGaO ₃ layer; The gate and the conductive substrate are used for external vertical electric field. 5 . The gallium oxide transistor according to claim 4 , wherein the thickness of the ε-AlGaO ₃ layer is 5 nm to 30 nm. 6 . 6 . The gallium oxide transistor according to claim 4 , wherein the thickness of the ε-Ga ₂ O ₃ layer is 200 nm to 1000 nm. 7 . 7 . The gallium oxide transistor according to claim 4 , wherein the ε-AlGaO ₃ has spontaneous polarization along the c-axis direction. 8 . 8 . The gallium oxide transistor according to claim 4 , wherein the ε-Ga ₂ O ₃ has spontaneous polarization along the c-axis direction. 9 .

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