Silicon-based GaN radio frequency epitaxial structure with low current collapse

Abstract

The utility model discloses a silicon-based GaN radio frequency epitaxial structure with low current collapse. The epitaxial structure comprises a Si substrate, an AlN nucleating layer, an AlGaN buffer layer, a Fe-doped GaN layer, a GaN buffer layer, an AlGaN gradient back barrier layer, a GaN channel layer, an AlN barrier layer and a GaN cap layer, wherein the Si substrate, the AlN nucleating layer, the AlGaN buffer layer, the Fe-doped GaN layer, the GaN buffer layer, the AlGaN gradient back barrier layer, the GaN channel layer, the AlN barrier layer and the GaN cap layer are sequentially stacked from bottom to top. According to the utility model, through the AlGaN gradient back barrier layer, on one hand, the barrier height below the channel layer is raised, the electric leakage of the buffer layer is reduced, and the current collapse of the device is effectively inhibited; on the other hand, the migration rate of the 2DEG is improved while the higher 2DEG concentration is ensured, and the saturated drain current of the device is increased. The ultra-thin GaN cap layer with good surface appearance is grown by using extremely low Ga source flow, so that grid leakage and current collapse are effectively inhibited while the device is ensured to have high-saturation drain current.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of semiconductor device, especially relate to a low current collapse's silicon base GaN radio frequency epitaxial structure. BACKGROUND

[0002] GaN-based semiconductor material has great advantages in high-frequency and high-power applications due to its high thermal conductivity, high breakdown field strength, wide band gap width and high electron saturation velocity. In recent years, GaN-based HEMT devices have developed rapidly and have been widely used in aerospace, communication and other fields, but many problems have been found in practical application. For example, the current collapse phenomenon of the device under high temperature and high pressure environment, which seriously affects the reliability of the device. Khon et al. proposed a virtual gate model, which pointed out that the electrons tunnel to the surface of the device are captured by surface defects, forming a virtual gate, which reduces the 2DEG concentration. In addition, researchers found that 2DEG also exists in the phenomenon of overflow into the buffer layer trap under high voltage bias, which also causes current collapse.

[0003] For the traps on the surface of the epitaxial wafer, a better processing method is to introduce a SiN x cap layer or a GaN cap layer, both of which can passivate the surface of the device, change the density of the surface defect state or the charging and discharging capacity, so that the current collapse is inhibited. However, the growth of GaN on the AlN layer is mostly in 3D-2D growth mode, which makes it more difficult to obtain good surface morphology for thinner GaN layers. Poor surface morphology means higher surface defect state density, which directly affects the gate leakage and current collapse of the device. The common method is to grow a thicker GaN cap layer (2-3nm), but this will inevitably reduce the polarization strength of the barrier layer and reduce the current size. Therefore, it is necessary to improve the growth quality of the cap layer through process adjustment. For the current collapse caused by the charging and discharging of the deep traps in the buffer layer, the AlGaN back barrier layer can inhibit the downward movement of 2DEG. Generally speaking, the higher the thickness and Al component of the back barrier, the smaller the probability of electron tunneling through the back barrier, and the better the inhibition effect on current collapse. However, due to the smaller lattice constant of AlN than GaN, increasing the Al component or the thickness of the AlGaN back barrier will inevitably cause greater compressive stress on the channel GaN, which will seriously affect the piezoelectric polarization strength of the heterojunction and reduce the 2DEG concentration (a kind of semiconductor structure (CN212136452U)). UTILITY MODEL CONTENTS

[0004] The utility model discloses to the current collapse problem of GaN base HEMT, proposes a low current collapse's silicon base GaN radio frequency epitaxial structure.

[0005] The purpose of the utility model is realized at least by one of the following technical schemes.

[0006] A silicon-based GaN radio frequency epitaxial structure with low current collapse, comprising, from bottom to top, a Si substrate with a crystal orientation of (111), an AlN nucleation layer, an AlGaN buffer layer, a Fe-doped GaN layer, a GaN buffer layer, an AlGaN gradient back barrier layer, a GaN channel layer, an AlN barrier layer, and a GaN cap layer;

[0007] The AlGaN gradient back barrier layer comprises a plurality of Al x Ga 1-x N layers with an Al component x increasing in gradient from bottom to top, and the growth time of each Al x Ga 1-x N layer is the same; under the same thickness, the AlGaN gradient back barrier layer has a breakdown voltage improvement and current collapse suppression effect close to that of a conventional fixed-component Al 0.5 Ga 0.5 N back barrier, but has less negative impact on 2DEG concentration.

[0008] The GaN cap layer is grown using a set trimethylgallium flow rate, and the trimethylgallium flow rate is 2-30 sccm / min, which improves the growth quality and the surface root mean square roughness (5mm x 5mm) is not higher than 0.21nm.

[0009] The Fe-doped GaN layer is a GaN layer doped with Fe to suppress buffer layer leakage of the device and improve the breakdown voltage of the device.

[0010] Further, the AlN nucleation layer, the AlGaN buffer layer, the Fe-doped GaN layer, the GaN buffer layer, the AlGaN gradient back barrier layer, the GaN channel layer, the AlN barrier layer, and the GaN cap layer are all grown using a metal organic chemical vapor deposition technique.

[0011] Further, the Si substrate has a size of 6 inches, a thickness of 1000μm, and a resistivity of 5000Ω·cm or higher.

[0012] Further, the AlN nucleation layer has a thickness of 100-150nm and is grown on the Si substrate.

[0013] Further, the AlGaN buffer layer has a thickness of 300-400nm and an Al component of 0.25-0.35, and is grown on the AlN nucleation layer.

[0014] Further, the Fe-doped GaN layer has a thickness of 600-700nm and is grown on the AlGaN buffer layer.

[0015] Further, the GaN buffer layer has a thickness of 400-600nm and is grown on the Fe-doped GaN layer.

[0016] Further, the thickness of the AlGaN gradient back barrier layer is 10-20 nm, the Al x Ga 1-x N layer is the same, and the Al x Ga 1-x N layer is 0, and the Al component x of the Al

[0017] Further, the thickness of the GaN channel layer is 180-220 nm, and the GaN channel layer is grown on the AlGaN gradient back barrier layer.

[0018] Further, the thickness of the AlN barrier layer is 7-12 nm, and the AlN barrier layer is grown on the GaN channel layer.

[0019] Further, the thickness of the GaN cap layer is 0.2-1 nm, the flow rate of trimethyl gallium is controlled to be 2-30 sccm / min, and the flow rate of NH3 is controlled to be 2-20 slm / min during the growth process, and the GaN cap layer is grown on the AlN barrier layer.

[0020] The silicon-based GaN radio frequency epitaxial structure with low current collapse can be prepared through the following steps:

[0021] Step one, place the Si substrate in the MOCVD reaction cavity for high-temperature annealing treatment;

[0022] Step two, pre-flow trimethyl aluminum for 10 s under the environment of a set temperature and pressure;

[0023] Step three, epitaxially grow an AlN nucleation layer on the Si substrate;

[0024] Step four, epitaxially grow an AlGaN buffer layer on the AlN nucleation layer;

[0025] Step five, epitaxially grow a Fe-doped GaN layer on the AlGaN buffer layer, and flow ferrocene to realize Fe doping;

[0026] Step six, epitaxially grow a GaN buffer layer on the Fe-doped GaN high-resistance buffer layer without flowing ferrocene;

[0027] Step seven, grow an AlGaN gradient back barrier layer on the GaN buffer layer, and the growth time of each Al x Ga 1-x N layer is the same, and the Al component is increased from 0 to 1 in an equal gradient from bottom to top, so that the buffer layer leakage and current collapse of the device can be effectively inhibited while ensuring a high 2DEG density;

[0028] Step eight, grow a GaN channel layer on the AlGaN gradient back barrier layer.

[0029] Step nine, growing an AlN barrier layer on the GaN channel layer;

[0030] Step ten, growing a GaN cap layer on the AlN barrier layer, controlling the trimethyl gallium flow rate to be 2-30sccm / min and the NH3 flow rate to be 2-20slm / min to form a thin film with good surface, reduce the defect density in the GaN cap layer, so as to achieve the effect of inhibiting the gate leakage and current collapse of the device.

[0031] Compared with the prior art, the utility model has the advantages of:

[0032] The utility model adopts Si substrate instead of SiC substrate, can effectively reduce cost, is equipped with AlGaN gradient back barrier layer, guarantees higher 2DEG concentration, improves breakdown voltage, and inhibits current collapse caused by buffer layer deep energy level charging and discharging. The growth thickness of the GaN cap layer is adjusted, the super-thin GaN cap layer with good surface morphology is epitaxially grown through extremely low trimethyl gallium flow, and the current collapse caused by surface defect state charging and discharging is inhibited.

[0033] By growing AlGaN gradient back barrier, Al component is gradiently increased from bottom to top, and each layer Al x Ga 1-x N growth time is same. At the same thickness, its breakdown promotion and current collapse inhibition effect to the device are close to those of the conventional fixed component Al 0.5 Ga 0.5 N back barrier, but its negative influence on 2DEG concentration is smaller. On the other hand, the parameters of the GaN cap layer are optimized, are grown with extremely low trimethyl gallium flow (2-30sccm / min), the surface morphology is optimized, the surface trap density is reduced, and the current collapse is further inhibited. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is structure schematic view of a silicon-based GaN radio frequency epitaxial structure with low current collapse in the embodiment of the utility model;

[0035] Figure 2 It is the schematic view of the change curve of the flow rate of trimethyl aluminum and trimethyl gallium with time in the epitaxial growth process of the gradient AlGaN back barrier layer of the embodiment 1 of the utility model;

[0036] Figure 3 It is the schematic view of the change curve of the flow rate of trimethyl aluminum and trimethyl gallium with time in the epitaxial growth process of the gradient AlGaN back barrier layer of the embodiment 2 of the utility model;

[0037] Figure 4The output characteristic and pulse I-V characteristic curve of the device made by the embodiment 1 and the embodiment 2 are shown in the figure. DETAILED DESCRIPTION

[0038] The low-current collapse silicon-based GaN radio frequency epitaxial structure is obtained through the structure optimization.

[0039] In order to further understand the present application, the specific implementation method of the present application is further described below in combination with the drawings and examples, but the implementation mode of the present application is not limited thereto.

[0040] As Figure 1 The present embodiment shows a low-current collapse silicon-based GaN radio frequency epitaxial structure, which comprises, from bottom to top, a Si substrate 1 with a crystal direction of (111), an AlN nucleation layer 2, an AlGaN buffer layer 3, an Fe-doped GaN layer 4, a GaN buffer layer 5, an AlGaN gradient back barrier layer 6, a GaN channel layer 7, an AlN barrier layer 8 and a GaN cap layer 9.

[0041] The AlGaN gradient back barrier layer 6 comprises multiple Al x Ga 1-x N layers with the Al component increasing from bottom to top in an equal gradient, and x is the Al component. x Ga 1-x The growth time of each Al 0.5 Ga 0.5 N layer is the same; under the same thickness, the breakdown voltage improvement and current collapse suppression effect of the AlGaN gradient back barrier layer 6 on the device is close to that of the conventional fixed-component Al

[0042] The GaN cap layer 9 is grown by setting the trimethylgallium flow rate, the trimethylgallium flow rate is 2-30 sccm / min, the growth quality is improved, and the surface root mean square roughness (5mm*5mm) is not higher than 0.21nm.

[0043] The Fe-doped GaN layer 4 is a GaN layer doped with Fe to improve the breakdown voltage of the device.

[0044] Preparation of embodiment 1:

[0045] A manufacturing method of a low-current collapse silicon-based GaN radio frequency epitaxial structure, the steps are as follows:

[0046] Step one, high temperature annealing treatment was performed on the 6 inch high resistance Si substrate 1 in the MOCVD reaction chamber, the temperature was 1090℃, and the annealing time was 10 min.

[0047] Step two, trimethylaluminum was pre-passed at a temperature of 1090℃ and a pressure of 75 Torr for 10 s.

[0048] Step three, an AlN nucleation layer was epitaxially grown on the Si substrate 1, the growth time was 37 min, and the growth thickness was 150 nm.

[0049] Step four, an AlGaN buffer layer 3 was epitaxially grown on the AlN nucleation layer 2, the Al component was 0.30, the corresponding growth time was 40 min, and the growth thickness was 400 nm.

[0050] Step five, a Fe-doped GaN layer 4 was epitaxially grown on the AlGaN buffer layer 3, ferrocene was introduced to achieve Fe doping, the doping concentration was 6×10 17 cm -2 -6, the growth time was 16 min, and the growth thickness was 640 nm.

[0051] Step six, a GaN buffer layer 5 was epitaxially grown on the Fe-doped GaN layer 4 without introducing ferrocene, the growth time was 14 min, and the growth thickness was 560 nm.

[0052] Step seven, an AlGaN gradient back barrier layer 6 was grown on the GaN buffer layer 5, the Al x Ga 1-x component of each AlGaN gradient back barrier layer 6 layer was 0 / 0.33 / 0.66 / 1 from bottom to top, each growth time was 2 min, and the total growth thickness was 20 nm.

[0053] Step eight, a GaN channel layer 7 was grown on the AlGaN gradient back barrier layer 6, the growth time was 5 min, and the growth thickness was 200 nm.

[0054] Step nine, an AlN barrier layer 8 was grown on the GaN channel layer 7, the growth time was 120 s, and the growth thickness was 8 nm.

[0055] Step ten, a GaN cap layer 9 was grown on the AlN barrier layer 8, the trimethylgallium flow rate was controlled at 15 sccm / min, the NH3 flow rate was 10 slm / min, the time was 50 s, and the growth thickness was 1 nm.

[0056] At this point, the preparation of the silicon-based GaN radio frequency epitaxial structure with low current collapse was completed.

[0057] Preparation Example 2

[0058] A silicon-based GaN radio frequency epitaxial structure with low current collapse and a manufacturing method thereof, steps as follows:

[0059] Step one, put 6 inch high resistance Si substrate 1 into MOCVD reaction cavity for high temperature annealing treatment, temperature 1090℃, annealing time 10 min.

[0060] Step two, pre-pass trimethylaluminum at temperature 1090℃, pressure 75 Torr, time 10 s.

[0061] Step three, epitaxially grow AlN nucleation layer on Si substrate 1, time 37 min, growth thickness 150 nm.

[0062] Step four, epitaxially grow AlGaN buffer layer 3 on AlN nucleation layer 2, Al component 0.30, corresponding growth time 40 min, growth thickness 400 nm.

[0063] Step five, epitaxially grow Fe-doped GaN layer 4 on AlGaN buffer layer 3, pass ferrocene to realize Fe doping, doping concentration 6×10 17 cm -2 , growth time 16 min, growth thickness 640 nm.

[0064] Step six, epitaxially grow GaN buffer layer 5 on Fe-doped GaN layer 4, without passing ferrocene, growth time 14 min, growth thickness 560 nm.

[0065] Step seven, grow AlGaN gradient back barrier layer 6 on GaN buffer layer 5, Al x Ga 1-x component of each layer of AlGaN gradient back barrier layer 6 is 0 / 0.5 / 1 from bottom to top, each growth time is 2 min, growth thickness is 15 nm.

[0066] Step eight, grow GaN channel layer 7 on AlGaN gradient back barrier layer 6, growth time 5 min, growth thickness 200 nm.

[0067] Step nine, grow AlN barrier layer 8 on GaN channel layer 7, growth time 120 s, growth thickness 8 nm.

[0068] Step ten, grow GaN cap layer 9 on AlN barrier layer 8, control trimethylgallium flow rate to be 15 sccm / min, NH3 flow rate to be 10 slm / min, time to be 25 s, growth thickness to be 0.5 nm.

[0069] At this point, the preparation of the silicon-based GaN radio frequency epitaxial structure with low current collapse is completed.

[0070] Compared with the embodiment 1, the thickness of the AlGaN gradient back barrier layer is lower and the component gradient is larger, and the GaN cap layer is thinner, which means that the piezoelectric polarization strength of the channel GaN is larger, the 2DEG concentration and the saturation drain current are larger. But due to the thinning of the cap layer and the back barrier layer, the difficulty of the electron vertical tunneling is reduced, and the current collapse of the device is larger.

[0071] Figure 2 The figure is a schematic diagram of the flow rate change curve of trimethylaluminum and trimethylgallium in the epitaxial growth process of the gradient AlGaN back barrier layer 6 of the embodiment 1 of the utility model;

[0072] Figure 3 The figure is a schematic diagram of the flow rate change curve of trimethylaluminum and trimethylgallium in the epitaxial growth process of the gradient AlGaN back barrier layer 6 of the embodiment 2 of the utility model;

[0073] Figure 4 The figure is the output characteristic and pulse I-V characteristic curve diagram of the device made of the embodiment 1 and the embodiment 2 of the utility model; the saturation drain current of the embodiment 1 is higher than that of the traditional structure HEMT, and the improvement range is about 9.6%. The current collapse (saturation current drop range) of the embodiment 1 is about 22%, and the current collapse of the traditional epitaxial structure HEMT is about 27%.

[0074] The above-mentioned embodiments are only preferred embodiments of the utility model, and cannot be used to limit the protection scope of the utility model. The person skilled in the art can make various non-essential modifications and changes on the basis of the utility model, and all of them belong to the protection scope required by the utility model.

Claims

1. A low current collapse silicon based GaN RF epitaxial structure, characterized by: The Si substrate (1) with crystal orientation (111), the AlN nucleation layer (2), the AlGaN buffer layer (3), the Fe-doped GaN layer (4), the GaN buffer layer (5), the AlGaN gradient back barrier layer (6), the GaN channel layer (7), the AlN barrier layer (8) and the GaN cap layer (9) are stacked in sequence from bottom to top. Wherein, the AlGaN gradient back barrier layer (6) comprises multiple Al x Ga 1-x N layers, each layer has the same growth time, and x is the Al component. x Ga 1-x N layers, each layer has the same growth time, and x is the Al component. The GaN cap layer (9) is grown by trimethylgallium; and the Fe-doped GaN layer (4) is a Fe-doped GaN layer.

2. A low current collapse silicon based GaN RF epitaxial structure as claimed in claim 1, wherein: The Si substrate (1) has a resistivity of 5000 Ω·cm or above.

3. A low current collapse silicon based GaN RF epitaxial structure as claimed in claim 1, wherein: The AlN nucleation layer (2) has a thickness of 100-150 nm and is grown on the Si substrate (1).

4. A low current collapse silicon based GaN RF epitaxial structure as claimed in claim 1, wherein: The AlGaN buffer layer (3) has a thickness of 300-400 nm.

5. A low current collapse silicon based GaN RF epitaxial structure as claimed in claim 1, wherein: The Fe-doped GaN layer (4) has a thickness of 600-700 nm and is grown on the AlGaN buffer layer (3). The GaN buffer layer (5) has a thickness of 400-600 nm and is grown on the Fe-doped GaN layer (4).

6. A low current collapse silicon based GaN RF epitaxial structure as claimed in claim 1, wherein: The total thickness of the AlGaN gradient back barrier layer (6) is 10-20 nm, and each Al layer... x Ga 1-x The growth time of the N layers is the same, and the Al layers from bottom to top are all... x Ga 1-x The Al component x of the N layer increases from 0 to 1, growing on top of the GaN buffer layer (5).

7. A low current collapse silicon based GaN RF epitaxial structure as claimed in claim 1, wherein: The GaN channel layer (7) has a thickness of 180-220 nm and is grown on the AlGaN gradient back barrier layer (6).

8. A low current collapse silicon based GaN RF epitaxial structure as claimed in claim 1, wherein: The AlN barrier layer (8) has a thickness of 7-12 nm and is grown on the GaN channel layer (7).

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