TW201924045A - Nitride semiconductor epitaxial substrate and high electron mobility transistor using the nitride semiconductor - Google Patents

Abstract

There is provided a nitride semiconductor epitaxial substrate having a spacer structure capable of obtaining characteristics unprecedented in the prior art. In the nitride semiconductor epitaxial substrate of the present invention, a channel layer, a spacer layer, and an electron supply layer are stacked in this order. The channel layer is GaN. The spacer layer is AlaGa1-aN (0 < a < 0.5). The electron supply layer is AlxInyGa1-x-yN (0 < x+y ≤ 1). The spacer layer has a thickness of two molecular layers or less. Thus, adverse effects due to the existence of a conventional spacer layer are suitably suppressed.

Description

Nitride semiconductor epitaxial substrate and nitride semiconductor high electron mobility transistor

The present invention relates to a substrate structure for improving the performance of a device in a nitride semiconductor epitaxial substrate to which a high frequency, high output power device is applied.

In the case of a high electron mobility transistor (HEMT) using a nitride semiconductor, particularly a semiconductor substrate having a nitrided compound semiconductor, it is known to sandwich a so-called spacer layer between the electron walking layer and the electron supply layer. To improve the technology of electricity.

The technique disclosed in Japanese Laid-Open Patent Publication No. 2004-200711 is as follows. That is, a nitride-based III-V compound semiconductor device having a heterostructure includes: a first binary compound semiconductor layer constituting a channel layer; and a ternary mixed crystal semiconductor layer composed of AlGaN, which constitutes a barrier a layer, a composition ratio of Al to Ga is constant; and a second binary compound semiconductor layer interposed between the first binary compound semiconductor layer and the ternary mixture Further, in the first binary compound semiconductor layer-based GaN, the second binary compound semiconductor layer layer has a thickness of one molecule or more and four or less layers of AlN.

The compound semiconductor device disclosed in Japanese Laid-Open Patent Publication No. 2003-229439 has an electron supply layer, a spacer layer, and a channel layer which are made of a nitride of a group III element which is necessary for Ga, respectively, in a lattice matching form. In the structure formed by bonding, the spacer layer is composed of an AlGaN layer, and an AlN mixed crystal of a region of the spacer layer in contact with the channel layer is higher than a remaining region.

In the invention of Japanese Laid-Open Patent Publication No. 2004-200711, it is considered that when the separation layer, that is, the second binary compound semiconductor layer is made of AlN, since AlN has a maximum energy band gap of 6.2 eV, if the layer thickness is changed When the thickness is too large, the current injection from the barrier layer to the channel layer is prevented from becoming a function of the heterostructure. Therefore, by setting the film thickness to 1 molecule or more and 4 or less layers, the bonding interface can be kept steep. The tunneling effect is used for sufficient carrier transport.

The invention of Japanese Laid-Open Patent Publication No. 2003-229439 is not directed to the entire AlGaN spacer layer, but makes it possible to most expect an AlN mixed crystal region which is the region of the piezoelectric field effect of the 2DEG layer, that is, the boundary region between the AlGaN spacer layer and the channel layer. The selectivity is increased relative to the remaining area in order to solve this problem. That is, the AlN mixed crystal ratio is not increased for the entire partition layer, but only for the boundary region, specifically, the thickness of the separation layer is maintained to the extent that lattice relaxation is not caused to increase the AlN mixed crystal ratio, thereby greatly increasing The effect of applying a piezoelectric field to the channel layer is increased. In addition, by When the AlN mixed crystal ratio of the junction region is increased, the bottom energy level Ec of the conduction layer on the partition layer side is increased, the discontinuous value of the conduction band is further increased, and the spontaneous polarization effect is also improved. Thereby, a deeper and narrower triangular potential can be formed on the channel layer side than the structure in which the spacer layer is formed by the same composition, and an increase in the electron concentration in the 2DEG layer and an increase in the output of the element can be achieved.

As such, although any of the above inventions can be said to be a useful technique in terms of the structure of the HEMT, it is difficult to say that the thinner separation layer is sufficiently fully reviewed, and there is room for further improvement.

The present invention has been made in view of the above problems, and an object of the invention is to provide a nitride semiconductor epitaxial substrate and a nitride semiconductor high electron mobility transistor, which are not only have a structure of a thin spacer layer, but are also applicable to a high performance nitride semiconductor device.

The nitride semiconductor epitaxial substrate of the present invention has a layer structure in which a channel layer, a spacer layer, and an electron supply layer are sequentially laminated, the channel layer is GaN, and the spacer layer is Al _a Ga _1-a N (0<a<0.5), the electron supply layer is Al _x In _y Ga _1-xy N (0<x+y≦1), and the layer thickness of the separator layer is 2 molecules or less.

Conventionally, there has been a problem that the current collapse suppressing effect cannot be sufficiently obtained due to the existence of the spacer layer. However, by having the above-described related configuration, it is possible to obtain a nitride semiconductor epitaxial substrate which is remarkably improved.

Further, a nitride semiconductor HEMT using such a nitride semiconductor epitaxial substrate is suitable for use in a more excellent electrical property.

According to the present invention, it is possible to provide a nitride semiconductor epitaxial substrate, which is incapable of obtaining a current collapse suppressing effect due to the presence of a spacer layer. This problem is remarkably improved, and the nitride semiconductor HEMT using the nitride semiconductor epitaxial substrate can be utilized. Excellent electrical properties.

1‧‧‧Base substrate

2‧‧‧Barrier layer

3‧‧‧GaN layer (channel layer)

4‧‧‧AlGaN layer (electron supply layer)

S‧‧‧ separation layer

Z‧‧‧ nitride semiconductor substrate

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic cross-sectional view showing a state of a nitride semiconductor epitaxial substrate of the present invention.

2 is a cross-sectional view showing the vicinity of the electron supply layer 4/separator layer S/channel layer 3 of Comparative Example 1 and Example 1, and the elements obtained by STEM-EDS (Scanning Transmission Electron Microscopy-Energy Dispersive Spectroscopy). Figure of the result.

3 is a bright-field STEM image (left), HAADF-STEM (High-Angle) in the case where the vicinity of the electron supply layer 4/separator layer S/channel layer 3 of Example 1 is subjected to cross-sectional STEM observation at a low magnification as shown in FIG. Annular Dark-Field Scanning Transmission Electron Microscopy) (right).

Hereinafter, the present invention will be described in detail with reference to the drawings. The nitride semiconductor epitaxial substrate of the present invention has a layer structure in which a channel layer 3, a spacer layer S, and an electron supply layer 4 are sequentially laminated, the channel layer 3 is GaN, and the spacer layer S is Al _a Ga _1-a N (0 < a < 0.5), the electron supply layer 4 is Al _x In _y Ga _1-xy N (0 < x + y ≦ 1), and the layer thickness of the spacer layer S is 2 molecular layers or less.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic cross-sectional view showing a state of a nitride semiconductor epitaxial substrate of the present invention. Further, the drawings shown in the present invention are all schematically simplified and emphasized, for the sake of explanation, and the shapes, sizes, and ratios of the details are different from actual ones.

On the nitride semiconductor substrate Z shown in FIG. 1, a barrier layer 2, a channel layer 3, a spacer layer S, and an electron supply layer 4 are sequentially formed on the base substrate 1. Further, although not shown, an electrode can be further provided by providing an electrode and a cap layer as necessary.

In the present invention, the HEMT having a heterogeneous interface and using the two-dimensional electron gas (2DEG) generated in the vicinity of the interface as a current path can particularly exhibit appropriate characteristics. The material, physical properties, structure, and manufacturing method of the base substrate 1 and the barrier layer 2 are not particularly limited, and a well-known method can be widely used.

The base substrate 1 may be a germanium single crystal, tantalum carbide, sapphire, or gallium nitride (GaN). Among these materials, the tantalum single crystal has an unfavorable tendency in terms of the longitudinal withstand voltage compared with the more rigid tantalum carbide, sapphire, etc., but it is suitable in terms of ease of large diameter and low cost. Therefore, the present invention exemplifies a nitride semiconductor substrate using a germanium single crystal.

The barrier layer 2 can be applied, for example, to a barrier layer structure disclosed in Japanese Patent No. 5159858 or Japanese Patent No. 5188545. Specifically, it is applicable to: a layer composed of AlN having a thickness of 50 nm to 200 nm in the first layer and AlGaN having a thickness of 100 nm to 300 nm in the second layer; or an Al _x Ga _1-x N single crystal layer (0.6) ≦x≦1.0) and Al _y Ga _1-y N single crystal layer (0≦y≦0.5) are sequentially alternately laminated from the substrate side, and the Al _x Ga _1-x N single crystal layer (0.6≦x) ≦1.0) contains carbon of 1×10 ¹⁸ atoms/cm ³ to 1×10 ²¹ atoms/cm ³ , and the Al _y Ga _1-y N single crystal layer (0≦y≦0.5) contains carbon of 1×10 ¹⁷ A multilayer barrier layer of atoms/cm ³ to 1 × 10 ²¹ atoms/cm ³ . Further, if the barrier layer of high resistance which is in contact with the channel layer 3 is, for example, a GaN layer having a carbon concentration of 1×10 ¹⁸ atoms/cm ³ to 3×10 ¹⁸ atoms/cm ³ and a thickness of 100 nm to 200 nm, It is particularly preferable to exert the vertical pressure withstand effect of the GaN layer.

In the present invention, the channel layer 3 is composed of a nitride semiconductor of a group 13 element, and the electron supply layer 4 is composed of a nitride semiconductor of a group 13 element and a group 13 element. The group 13 elements are gallium (Ga), aluminum (Al), and indium (In). In the present invention, the first group 13 element is any one of Ga, Al, and In, and the second group 13 element is any element other than Ga, Al, and In, but is a group other than the group 13 element. The combination of the Group 13 and Group 13 elements of Ga and the Group 2 and Group 13 elements of Al is suitable for the degree of substrate design freedom.

The layer thickness of the channel layer 3 and the electron supply layer 4 is not particularly limited, and is approximately 0.3 μm to 3.0 μm with respect to the channel layer 3 and 10 nm to 100 nm with respect to the electron supply layer 4. Further, the electron supply layer 4 may also be doped with various elements. Examples of the various elements include carbon, phosphorus, magnesium, barium, iron, oxygen, hydrogen, and the like.

In the present invention, a partition layer S is provided between the channel layer 3 and the electron supply layer 4. This separation layer S is basically for the purpose of obtaining the same function as the separation layer in the prior art, and aims to achieve both an increase in output and an increase in electron mobility due to an increase in the concentration of the two-dimensional electron gas in the HEMT.

The present invention is characterized in that the partition layer S is Al _a Ga _1-a N (0 < a < 0.5), and the electron supply layer 4 is Al _x In _y Ga _1-xy N (0 < x + y ≦ 1) The layer thickness of the separator layer S is 2 molecular layers or less. Among them, in particular, the layer thickness of the separator layer S is 2 molecular layers or less.

Such a form can be observed by scanning a through-hole electron micromirror (STEM) to observe the cross section of the nitride semiconductor substrate Z and performing elemental analysis by energy dispersive X-ray spectroscopy (EDS). 2 is a cross-sectional view showing the vicinity of the electron supply layer 4/separator layer S/channel layer 3 of Comparative Example 1 and Example 1 by STEM, showing STEM-for the vicinity of the electron supply layer 4/separator layer S/channel layer 3. The results obtained by EDS analysis. Further, EDS is measured by an EDS measuring device attached to a STEM device.

In addition, the value obtained by EDS is based on the measurement principle, so the numerical value is only a reference value at best, but the ratio of the existence of different elements to each other can be correctly reflected, and the present invention can also roughly understand exactly what kind of distribution of the element A which is the object.

The spacer layer S has _a composition of Al _a Ga _1-a N (0 < a < 0.5). In order to function as a separation layer, that is, to improve mobility, Al must exist to some extent. As long as the channel layer 3 is GaN as in the present invention, the Al composition a can exhibit a mobility improvement effect from a degree of 0.1, and the larger the a, the higher the effect.

On the other hand, since the spacer layer S is directly in contact with the channel layer 3 composed of GaN, once the difference in lattice constant between the spacer layer S and GaN is larger than that of a, the difference in density will be due to the interface The resulting strain increases. This increased difference in density is considered to be one of the causes of the deterioration of the current collapse.

Further, in the case where a layer is formed by a metal-organic vapor phase growth method (MOCVD method), a separator layer S having a composition of Al _a Ga _1-a N (0 < a < 0.5) is compared. The fact that GaN contains more carbon can be said to make the current collapse worse.

Further, if the thickness of the spacer layer S having a composition of Al _a Ga _1-a N (0 < a < 0.5) is thin, it can be more lattice-matched with the GaN of the channel layer, so that it is less likely to enter into defects. The suppression of current collapse has an effect. However, if the thickness is the same, once a is increased, the difference in lattice constant between the spacer layer S and GaN is increased, so that the amount of defects occurring in the channel layer made of GaN is increased.

In summary, it can be said that when the spacer layer S is composed of Al _a Ga _1-a N (0 < a < 0.5), the thinner the thickness, the smaller a is from the viewpoint of the current collapse suppressing effect. The better, but if a does not reach the predetermined value or more, the mobility cannot be improved.

Based on the above points, the following description of the differences between the present invention and the prior art will be described in detail.

Japanese Laid-Open Patent Publication No. 2004-200711 exemplifies a separation layer of AlN having a layer thickness of 1 molecular layer or more and 4 molecular layers or less. That is, for the disadvantages of AlN, that is, the current injection barrier of the self-blocking layer toward the channel layer Try to respond by thinning the layer thickness. However, if AlN is directly in contact with GaN, it cannot be denied that the high carbon concentration of the AlN layer eventually moves in the direction of deterioration of performance due to the difference in the interface between the layers and the AlGaN layer.

In Japanese Laid-Open Patent Publication No. 2003-229439, the ratio of Al atoms at the junction of the separation layer and the channel layer is increased with respect to the remaining portion, and further, in order to improve the suppression effect of alloy scattering, the separation layer is in contact with the channel layer. The part is preferably AlN, and the layer thickness of AlN is preferably a few atomic layers. That is, even Japanese Patent Laid-Open Publication No. 2003-229439 can be said to have the following technical idea: the portion where the separation layer is in contact with the channel layer is preferably AlN, and the disadvantage of AlN is reduced by reducing the layer thickness. .

In this regard, the present invention further examines the two parameters of the Al atomic ratio of the portion of the separation layer S that is in contact with the channel layer 3 and the layer thickness of the separation layer S, on the one hand, the thinning separation layer S, on the one hand From a new perspective, it is necessary to review how the ratio of the Al atomic ratio of the channel layer 3 to the spacer layer S affects the HEMT.

That is, focusing on the existence of the separation layer S causes deterioration of current collapse, and the following phenomenon is found, thereby completing the present invention. In the case of the separator described in JP-A-2004-200711 and JP-A-2003-229439, the Al atom ratio of the separator layer S composed of AlGaN is reduced and the thickness is reduced. Since AlGaN and the GaN constituting the channel layer 3 can be more lattice-matched, defects are less likely to enter and have an effect on suppression of collapse; and there is a effect as described above and The optimum value that causes serious damage to the mobility improvement effect of the original separation layer.

The present inventors have found that the above-described effects can be obtained by using the constitution in which the layer thickness of the partition layer S is 2 molecular layers or less. Since the separation layer S is necessary, the lower limit is one molecular layer. On the other hand, it is understood that if the partition layer S is too thick, it is disadvantageous in that the current collapse is deteriorated, so that the layer thickness is preferably 2 molecules or less.

In the present invention, the ratio of Al atoms in the partition layer S is appropriately evaluated by STEM-EDS. However, it is extremely difficult to accurately evaluate the Al atom ratio in a thickness of from 1 molecule to 2 molecules. Therefore, although high-precision quantification cannot be expected even with STEM-EDS, it is possible to distinguish between the electron supply layer 4 and the separation layer S, and to obtain an Al atom ratio substantially in each layer. .

Fig. 2 is a comparison between Comparative Example 1 and Example 1. For Comparative Example 1 in which the separation layer S was thick, the existence of the separation layer S can be clearly confirmed from the photograph. On the other hand, although the thickness of the layer was thin and the degree of resolution was not clear, even in the first embodiment, the color depth of a certain degree of recognition was confirmed. Further, with respect to Example 1, it seems that the separation layer S and the electron supply layer 4 have almost no difference in the atomic ratio of Al in the EDS pattern of FIG. 2, but the Al atomic ratio of the separation layer S is known from the analysis results of the numerical data. At 20%, the electron supply layer 4 has an Al atomic ratio of 15%.

3 is a view showing a clearer view when the boundary between the partition layer S of the cross-sectional view of the embodiment 1 shown in FIG. 2 and the electron supply layer 4 is more clearly seen at a lower magnification than that of FIG. STEM image (left) and HAADF-STEM image (right). Since the HAADF image becomes Z-contrast, the more light atoms in the analysis region (here, the higher the Al composition in AlGaN), the darker it appears. In Fig. 3, the brightest (GaN layer), the darkest (separator layer), and the three layers in which the contrast between the two (AlGaN electron supply layer) is different from each other can be confirmed in order from the bottom. In this manner, in the three portions of the channel layer of the present invention, it is possible to clearly confirm that there is a partition layer in which the Al composition is higher than that of the AlGaN electron supply layer.

In the comparison of the case where the Al atom ratio of the partition layer S is higher than the Al atom ratio of the electron supply layer 4 and the Al atom ratio of the partition layer S and the Al atom ratio of the electron supply layer 4, the original one can be more retained. The mobility enhancement effect of the separation layer is satisfactory.

Further, the atomic ratio of Al of the electron supply layer 4 is preferably between 10% and 30%. That is, it is preferable that _x in Al _x In _y Ga _1-xy N (0<x+y≦1) is 0.1 to 0.3, y is 0 to 0.9, and x+y≦1. The thickness of the electron supply layer 4 is also not particularly limited, and is designed from 10 nm to 60 nm in a timely manner.

The shape of the curve due to the ratio of Al atoms in the partition layer S can be adjusted by the MOCVD method for the flow rates of various material gases and carrier gases immediately after the formation of the channel layer 3, the pressure in the reactor, and the supply of the Al source gas. The timing is optimized and properly obtained.

In order to obtain the separation layer S and the electron supply layer 4 of the present invention by the MOCVD method, a suitable aspect is to form a channel layer composed of GaN using a Ga source gas and an N source gas in a reaction furnace of a vapor phase growth apparatus. After 3, when the separation layer and the electron supply layer are to be formed, use The Ga source gas, the N source gas, and the Al source gas are formed in a furnace pressure of 200 hPa to 300 hPa for 1.5 seconds to 10 seconds to form a separator layer S, thereby maintaining the film formation temperature at the time of formation of the separator layer, and rapidly changing the material. The supply ratio of the gas forms the aforementioned electron supply layer.

According to this method, even a method such as non-molecular vapor deposition can form a nitride semiconductor layer having a thickness of one molecule to two molecules by MOCVD.

As described above, the structure of the nitride semiconductor epitaxial substrate of the present invention has the effect of improving the mobility of the two-dimensional electron gas and increasing the speed of the transistor, as well as the separation layer. The current collapse characteristic is deteriorated, and the on-resistance of the AlGaN/GaN-HEMT device is lowered.

(Example)

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to the following examples.

[Common experimental conditions]

A tantalum single crystal substrate having a diameter of 6 inches, a thickness of 1000 μm, a p-type specific resistance of 0.01 Ω cm, and a plane orientation (111) was prepared as the base substrate 1. After the base substrate 1 is cleaned by a known substrate cleaning method, it is placed in an MOCVD apparatus, and after heat treatment and gas replacement, heat treatment is performed at a temperature of 1000 ° C for 15 minutes in a hydrogen atmosphere of 100% atmosphere and a furnace pressure of 135 hPa. The natural oxide film on the surface of the base substrate 1 is removed, so that the surface exhibits a helium atom ladder.

Next, trimethyl aluminum (TMAl; trimethyl aluminum) and ammonia (NH ₃ ) were used as raw material gases to form an AlN single crystal having a thickness of 70 nm. Next, the growth temperature was 1000 ° C, the furnace pressure was 60 hPa, and trimethyl gallium (TMG; trimethyl gallium), TMAl, and NH _{3 were} used as raw material gases to form an Al _0.1 Ga _0.9 N single crystal layer having a thickness of 300 nm. Next, using TMG, TMAl, and NH ₃ as raw material gases, an AlN single crystal layer having a thickness of 5 nm and an Al _0.1 Ga _0.9 N single crystal layer having a thickness of 30 nm were alternately laminated to form a multilayer structure having a layer thickness of about 2450 nm. In the above manner, the barrier layer 2 is formed on the base substrate 1 described above.

The growth temperature was 1030 ° C, the furnace pressure was 200 hPa, and a GaN single crystal layer having a thickness of 3000 nm was laminated on the barrier layer 2 as the channel layer 3.

The separator S (Al _a Ga _1-a N) is formed on the channel layer 3 under the conditions described in the first embodiment and the comparative example 1 to be described later.

Then, the growth temperature was 1000 ° C and the furnace pressure was 200 hPa, and an Al _0.18 Ga _0.82 N single crystal layer having a thickness of 24 nm was formed as the electron supply layer 4 on the spacer layer S, and a 4 nm GaN layer was formed as a cap layer. Through the above-described steps, a nitride semiconductor epitaxial substrate for evaluation was obtained. Further, the control of the thickness and carbon concentration of each layer formed by vapor phase growth is performed by adjusting the flow rate of the material gas, the supply time, the substrate temperature, and other well-known growth conditions.

[Example 1]

TMG, TMAl, and NH _{3 were introduced} as a material gas at a growth temperature of 1030 ° C and a furnace pressure of 200 hPa for 1.5 seconds, and a separator layer S was formed on the channel layer 3 as Example 1. As a result of evaluation in Fig. 2, the layer thickness of the spacer layer S was about 0.25 nm (1 molecule layer).

[Comparative Example 1]

TMG, TMAl, and NH _{3 were introduced} as a material gas at a growth temperature of 1030 ° C and a furnace pressure of 50 hPa for 10 seconds, and a separator layer S was formed on the channel layer 3 as Comparative Example 1. In this case, the Al content in the partition layer S becomes considerably higher than that in the first embodiment, and a high Al concentration region in which the Al composition ratio exceeds 50% is formed in the thickness direction. This layer has a thickness of about 1 nm (4 molecular layers).

With respect to the obtained nitride semiconductor epitaxial substrate of Example 1 and Comparative Example 1, cross-section observation and elemental analysis were performed on the partition layer S and a portion of the channel layer 3 and the electron supply layer 4 adjacent to the spacer layer S. The conditions for section observation and elemental analysis are as follows.

[Evaluation 1~STEM observation]

The individual nitride semiconductor epitaxial substrate was cleaved in the radial direction, and chips were sampled from the vicinity of the center of the main surface, and sliced by FIB (Focused Ion Beam) method to obtain a sample for measurement. This sample was observed by STEM (Scanning Through Electron Micromirror). The device used was JEM-ARM200F manufactured by JEOL Ltd., and the acceleration voltage was set to 200 kV. Further, the elemental analysis was carried out by an EDS measuring instrument (energy dispersive X-ray spectrometer) (JED-2300T) attached to the STEM used, and the measurement conditions were set to an acceleration voltage of 200 kV, a beam diameter of 0.1 nm φ, and energy decomposition energy. About 140eV.

[Evaluation 2~EDS Analysis]

After the STEM observation, the EDS measurement was performed by irradiating a 100-point light beam on the line in the vicinity of the electron supply layer 4/separator layer S/channel layer 3 over a width of 20 nm. The beam interval was 0.2 nm, and the measurement time per one point was 1 second.

In this measurement, in order to specify the form of the spacer layer S, one point near the center of the main surface of the nitride semiconductor epitaxial substrate was sampled. Since the film formation by the MOCVD method has high precision in film formation, it is sufficient to sample only one point. However, the number of samples may be increased depending on the necessity. For example, two places may be added to the inner side of the outer circumference of 10 mm, from a total of 3 points. Sampling.

[Evaluation 3~Electronic mobility]

Next, for the nitride semiconductor epitaxial substrate which was the same as the STEM observation and the EDS analysis, the Hall mobility measurement was performed based on the van der Pauw method to evaluate the electron mobility. Initially, the substrate was cut into 7 mm square wafers, and Ti/Al electrodes having a diameter of 0.25 mm were formed by vacuum evaporation at four corners on the electron supply layer 4 of each wafer. Next, alloying heat treatment was performed at 600 ° C for 5 minutes in an N ₂ atmosphere. Then, the Hall effect measurement was performed using an ACCENT HL5500PC.

[Evaluation 4~ Current Crash]

The evaluation of the current collapse characteristics was carried out in the following manner. First, the nitride semiconductor epitaxial substrate for evaluation described above is formed by dry etching to form a trench that is trapped in the recess gate region and the element isolation region, and is vacuum-deposited on the electron supply layer 4, respectively. An Au electrode is formed as a gate electrode, an Al electrode is formed as a source and a drain, and an Al electrode is formed as an inner surface electrode on the inner surface side of the base substrate. then, In the off state in which the HEMT element is fabricated, a constant DC voltage is applied between the source and the drain, and a constant called a collapse factor is calculated from the ratio of the conduction current flow rate in the on state before and after the application of the DC voltage. . The closer the value of the crash factor is to 1.0, the smaller the power-on loss of the component. The case where the crash factor is 0.7 to 1.0: good, 0.5 to less than 0.7: slightly bad, less than 0.5: bad.

As a result, the electron mobility of Example 1 was reduced by about 90% in comparison with Comparative Example 1, which is a difference in the extent that it would not be too much a problem in practical use. On the other hand, the current collapse was good in Example 1, and was slightly poor in Comparative Example 1.

According to the above results, it can be said that the embodiment 1 takes into consideration the electron mobility improvement effect and the current collapse suppression effect. On the other hand, in Comparative Example 1, the electron mobility was substantially equal to or higher than that in Example 1, but the current collapse suppression effect was inferior.

From this, it can be seen that the nitride semiconductor epitaxial substrate of the present invention can meaningfully obtain the current collapse suppressing effect without significantly impairing the electron mobility, and it can be said that it is particularly desirable to avoid the insertion of the spacer layer as much as possible. The adverse effects also hope to have a certain degree of separation effect, which is optimized for individual requirements.

Claims (2)

A nitride semiconductor epitaxial substrate having a layer structure in which a channel layer, a spacer layer, and an electron supply layer are sequentially laminated, wherein the channel layer is GaN, and the spacer layer is Al _a Ga _1-a N (0<a <0.5) The electron supply layer is Al _x In _y Ga _1-xy N (0<x+y≦1), and the layer thickness of the separator layer is 2 molecules or less. A nitride semiconductor high electron mobility transistor is a nitride semiconductor epitaxial substrate according to claim 1.