JP2006237539A - Method for manufacturing semiconductor element of group iii nitride compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the crystallinity of a semiconductor layer of a group III nitride compound which is doped with an acceptor impurity and contains at least aluminum. <P>SOLUTION: On a sapphire substrate 101, a buffer layer 102 made up of AlN, a layer 103 composed of non-doped GaN, an n-type contact layer 104 made up of GaN doped with silicon(Si), a multi-layer 105, a light emitting layer 106 composed of a multi quantum well layer where a barrier layer 1062 made up of non-doped GaN and a well layer 1061 made up of non-doped In<SB>0.2</SB>Ga<SB>0.8</SB>N are repeatedly formed, a p-type layer 107 composed of p-type Al<SB>0.2</SB>Ga<SB>0.8</SB>N doped with Mg, a layer 108 made up of non-doped Al<SB>0.02</SB>Ga<SB>0.98</SB>N, and a p-type contact layer 109 composed of p-type GaN doped with Mg in order. The p-type layer 107 is epitaxially grown under a mixed gas(nitrogen concentration 40-80%) of nitrogen and hydrogen, whereby, its light intensity is improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a group III nitride compound semiconductor device. The present invention particularly relates to a method for forming a group III nitride compound semiconductor layer containing at least aluminum, to which an acceptor impurity is added, by metal organic vapor phase epitaxy.

  In general, in the metal organic chemical vapor deposition method, a large amount of carrier gas is used when introducing a group III metal organic compound and ammonia into an epitaxial growth apparatus. Usually, nitrogen or hydrogen is used as the carrier gas. In order to introduce a raw material gas other than ammonia, particularly an organic metal, it is also common to introduce hydrogen or nitrogen saturated with an organic metal compound by bubbling the raw material container with hydrogen or nitrogen. When forming a group III nitride compound semiconductor layer containing indium by metal organic vapor phase epitaxy, it is often the case that only nitrogen is used as a carrier gas. When forming by a vapor phase growth method, only hydrogen may be used as a carrier gas. The above is cheap because hydrogen is inexpensive and easy to obtain a high-purity product, which is suitable for controlling the reaction system, but does not promote migration during the epitaxial growth of a group III nitride compound semiconductor layer containing indium. This is because pits are generated on the surface of the layer.

On the other hand, there are the following reports regarding epitaxial growth using a mixed carrier gas of hydrogen and nitrogen. These two patent documents relate to a method of manufacturing a GaN layer with the thin film growth surface held downward, as seen in the description of the examples.
Japanese Patent No. 3376849 Japanese Patent No. 3424507

  On the other hand, when forming a group III nitride compound semiconductor light emitting device, for example, when forming a layer including a wide band gap containing aluminum formed on the light emitting layer, the influence on the lower layer and the aluminum containing layer There has been a demand for further improvement in crystallinity. For example, when a clad layer containing aluminum is formed on a light-emitting layer containing indium, if the crystallinity of the clad layer is low, holes cannot be injected well into the light-emitting layer, or electrons are sufficiently injected into the light-emitting layer. Therefore, the recombination of electrons and holes in the light emitting layer is not performed efficiently, and the light emission efficiency is lowered.

  In view of the above-mentioned problems, the present invention has been conducted by earnestly examining the carrier gas in the vapor phase growth of a group III nitride compound semiconductor layer containing at least aluminum to which an acceptor impurity is added. It was completed by finding the range.

  In order to solve the above problems, according to the means of claim 1, in the method of manufacturing a semiconductor light emitting device having a group III nitride compound semiconductor layer containing at least aluminum to which an acceptor impurity is added, an acceptor impurity is provided. In a carrier gas in which a group III nitride compound semiconductor layer containing at least aluminum is added and is a mixed gas of hydrogen and nitrogen, and the ratio of nitrogen in the mixed gas is 40% or more and 80% or less Growing by metal organic vapor phase epitaxy.

  According to a second aspect of the present invention, a group III nitride compound semiconductor layer containing at least aluminum to which an acceptor impurity is added is formed immediately above the light emitting layer.

  As shown below, when vapor-phase-growing a group III nitride compound semiconductor layer containing at least aluminum to which an acceptor impurity is added, the carrier gas is a mixed gas of hydrogen and nitrogen, and the ratio of nitrogen in the mixed gas It has been found that the carrier mobility and the photoluminescence intensity can be increased, the surface roughness can be decreased, the aluminum composition distribution and the film thickness distribution can be reduced within the wafer by setting the ratio to 40% or more and 80% or less. . This is because by optimizing the range of nitrogen concentration (hydrogen concentration) in the carrier gas, the crystal quality of the group III nitride compound semiconductor layer containing aluminum is improved and the surface morphology is improved. Conceivable. Furthermore, such an effect can be considered to be due to the suppression of the generation of defects and surface roughness due to re-evaporation of atoms from the crystal during epitaxial growth (claim 1).

  Such a group III nitride compound semiconductor layer containing at least aluminum to which an acceptor impurity is added, for example, in a light-emitting element, is formed immediately above the light-emitting layer, so that a wider band gap than the light-emitting layer is formed. It will work well as a layer having (Claim 2). This is particularly effective for light emitting elements.

In the present application, the group III nitride semiconductor is at least a binary system represented by Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), A group III nitride compound semiconductor composed of a ternary or quaternary semiconductor is included. The layer to which the present invention is applied may be such that the aluminum composition x is not zero. Some of these group III elements may be replaced by boron (B) and thallium (Tl), and part of nitrogen (N) may be phosphorus (P), arsenic (As), antimony (Sb ) Or bismuth (Bi).

  Further, when an n-type group III nitride compound semiconductor layer is formed using these semiconductors, Si, Ge, Se, Te, C, etc. are added as donor impurities, and Zn as acceptor impurities. , Mg, Be, Ca, Sr, Ba and the like can be added. The layer to which the present invention is applied is one to which an acceptor impurity is added.

  In applying the present invention, the carrier gas only needs to be mainly composed of hydrogen and nitrogen, and may contain other inert gas such as argon. In addition, even if a carrier gas, various source gases, or other impurities are mixed by the apparatus when forming a layer grown before the target epitaxial growth layer by the so-called memory effect, it is included in the present invention. Needless to say. A desirable nitrogen concentration is 40 to 80%, more preferably 40 to 75%, still more preferably 50 to 70%, still more preferably 60 to 70%.

  When the present invention is applied to a group III nitride compound semiconductor device, it may be applied during the growth of a group III nitride compound semiconductor layer containing at least aluminum to which at least one acceptor impurity is added. The growth conditions are not limited to the growth conditions of the present invention. When applied to a light emitting element, it can be applied to a light emitting diode (LED), a laser diode (LD), a photocoupler, or any other light emitting element. In particular, a well-known manufacturing method can be used as a manufacturing method of the group III nitride compound semiconductor light emitting device.

  As the substrate for crystal growth, sapphire, spinel, Si, SiC, ZnO, MgO, a group III nitride compound single crystal, or the like can be used.

The light emitting layer may have a single layer, a single quantum well structure (SQW), a multiple quantum well structure (MQW), or any other configuration. When the light emitting layer has a multiple quantum well structure, it is composed of a group III nitride compound semiconductor Al _y Ga _1-yz In _z N (0 ≦ y <1, 0 <z ≦ 1) containing at least indium (In). It is preferable to include a well layer. The structure of the light emitting layer is composed of a well layer made of non-doped Ga _1-z In _z N (0 <z ≦ 1) and a group III nitride compound semiconductor AlGaInN having an arbitrary band gap larger than the well layer. And a barrier layer. A preferred example is a non-doped Ga _1-z In _z N (0 <z ≦ 1) well layer and a non-doped GaN barrier layer.

In the following examples, a sapphire substrate was used as a wafer, and vapor phase growth by metal organic vapor phase epitaxy (hereinafter referred to as “M0VPE”) was used. The gases used were NH ₃ , carrier gas H ₂ and N ₂ , trimethylgallium (Ga (CH ₃ ) ₃ ), trimethylaluminum (Al (CH ₃ ) ₃ ), trimethylindium (In (CH ₃ ) ₃ ), silane (SiH ₄ ) and cyclopentadienyl magnesium (Mg (C ₅ H ₅ ) ₂ ).

First, the carrier gas for forming Al _0.24 Ga _0.76 N doped with acceptor impurity magnesium was obtained by changing the mixing ratio of nitrogen and hydrogen, and obtaining the following data. The following data are obtained after the AlN buffer layer and the non-doped GaN layer are provided on the sapphire substrate and the Al _0.24 Ga _0.76 N: Mg layer is provided and the resistance is reduced under the same conditions. The thin film growth surface used an upward reaction device.

The nitrogen concentration in the carrier gas is shown as R = N ₂ / (N ₂ + H ₂ ). R is 0 to 1, and the case of R = 1, that is, the case where the carrier gas is only nitrogen is shown as Ref in the graph. In addition, nitrogen was used for the bubbler for supplying the gas of a metal raw material source. In the following, each data was obtained with R = 0, 0.2, 0.4, 0.6, 0.8, 1 in general, although there was a slight deviation for each data.

FIG. 1 is a graph comparing the intensity of photoluminescence of a p-Al _0.24 Ga _0.76 N: Mg layer with a wavelength of 326 nm against the nitrogen concentration R. R = 0.22, 0.44, 0.66, 0.88 with a mixed gas of hydrogen and nitrogen as opposed to R = 0 (Ref.) Where the carrier gas is only nitrogen and R = 0 where the carrier gas is only hydrogen. The intensity of luminescence was large, particularly when R = 0.22 and 0.44.

FIG. 2 is a graph comparing the hole mobility of the p-Al _0.24 Ga _0.76 N: Mg layer against the nitrogen concentration R. Variations in the center of the susceptor (shown as circles and in in the graph), outside (shown as squares and out in the graph), and the middle (shown as triangles and mid in the graph) However, the hole mobility increases as R decreases, that is, as the nitrogen concentration decreases, but measurement is impossible when R = 0, that is, only hydrogen is used as the carrier gas. This indicates that when only hydrogen is used as a carrier gas, excessive hydrogen is taken into the Al _0.24 Ga _0.76 N: Mg layer, and it is difficult to reduce the resistance.

FIG. 3 shows the surface roughness in terms of the root-mean-square (rms) with respect to the nitrogen concentration R. Compared with R = 1, that is, when only nitrogen was used as the carrier gas, rms decreased and the surface was flattened when hydrogen was mixed. This is thought to be due to active migration of atoms on the Al _0.24 Ga _0.76 N: Mg surface during epitaxial growth by mixing hydrogen into the carrier gas, contributing to planarization.

  FIG. 4 shows a comparison between the nitrogen concentration R and the Al composition calculated at the center of the susceptor and the outermost periphery of the susceptor. At R = 0, 0.22, 0.44, the Al composition variation exceeded 5%, but at R = 0.66, 0.88, 1 (Ref), the Al composition variation was 2% or less. This is because a carrier gas having a low nitrogen concentration (high hydrogen concentration) has a large temperature difference depending on the position of the susceptor, and a carrier gas having a high nitrogen concentration (low concentration of hydrogen) has a small temperature difference depending on the position of the susceptor. It depends. That is, since the carrier gas having a high nitrogen concentration (low hydrogen concentration) has a small temperature difference depending on the position of the susceptor, the variation of the Al composition depending on the position of the susceptor is also small.

FIG. 5 shows a comparison of the thickness of the p-Al _0.24 Ga _0.76 N: Mg layer measured at the center of the susceptor and the outermost periphery of the susceptor and the difference expressed in% with respect to the nitrogen concentration R. At R = 0, 0.22, the film thickness variation exceeded 10%, but at R = 0.44, 0.66, 0.88, the film thickness variation was less than R = 1 (Ref). The reason for this is considered that the nitrogen concentration R is related to the temperature difference depending on the position of the susceptor, similarly to the variation of the Al composition in FIG.

The above is summarized as shown in Table 1 below. In addition, since the experimental value of R was not uniform in each characteristic, the characteristic corresponding to the value of R was read from the graph and judged.

  From the point of PL intensity and hole mobility, there seems to be an optimum value in the vicinity of R = 0.2, but from the point of Al composition distribution and film thickness distribution, the characteristic is so bad that R = 0.2 cannot be used. Considering that the PL strength remains a characteristic that shows the crystallinity itself, the hole mobility should not be a problem as a layer that forms the device if the p-AlGaN: Mg layer has a certain level of conductivity. From the viewpoint of optimization of vapor phase growth conditions, it is thought that it is not so important.

  Then, it can be said that it is preferable to make the ratio of nitrogen into 40% or more and 80% or less from the point of Al composition distribution and film thickness distribution. In view of the hole mobility, the upper limit is lower than 80%, considering that a favorable high mobility with no variation is obtained at R = 0.22 and that a very low mobility without variation is obtained at R = 0.88. 75%, more preferably 70%, is considered preferable. On the other hand, the lower limit varies greatly between R = 0.44 and R = 0.66 in the Al composition distribution, so 50% is more preferable, and 60% or more is considered more preferable. From the above, the carrier gas is a mixed gas of hydrogen and nitrogen, the ratio of nitrogen in the mixed gas is preferably 40% or more and 80% or less, more preferably 40% or more and 75% or less, It is more preferable to set it as 50% or more and 70% or less, and it is still more preferable to set it as 60% or more and 70% or less.

FIG. 6 is a schematic cross-sectional view of a semiconductor light emitting device 100 according to an example of the present invention. In the semiconductor light emitting device 100, as shown in FIG. 6, a buffer layer 102 made of aluminum nitride (AlN) and having a thickness of about 10 nm is formed on a sapphire substrate 101 having a thickness of about 300 μm. A layer 103 made of GaN having a thickness of about 2 μm is formed, and an n-type contact layer 104 having a thickness of about 3 μm made of GaN doped with silicon (Si) 5 × 10 ¹⁸ / cm ³ (high carrier concentration n). ⁺ Layer) is formed.

On the n-type contact layer 104, a multi-layer of 90 nm is formed by stacking 20 pairs of a layer 1051 made of non-doped In _0.1 Ga _0.9 N having a thickness of 1.5 nm and a layer 1052 made of non-doped GaN having a thickness of 3 nm. A multilayer 105 is formed. Further thereon, a multiple quantum well layer 106 is formed in which a barrier layer 1062 made of non-doped GaN having a thickness of 17 nm and a well layer 1061 made of non-doped In _0.2 Ga _0.8 N having a thickness of 3 nm are formed in this order.

Further, a p-type layer 107 made of p-type Al _0.2 Ga _0.8 N having a thickness of 15 nm doped with Mg 2 × 10 ¹⁹ / cm ³ is formed on the multiple quantum well layer 106. A layer 108 made of non-doped Al _0.02 Ga _0.98 N having a thickness of 300 nm was formed on the mold layer 107. Further thereon, a p-type contact layer 109 made of p-type GaN having a thickness of 200 nm doped with 1 × 10 ²⁰ / cm ³ of Mg was formed.

  Further, a translucent thin film p-electrode 110 formed by metal deposition is formed on the p-type contact layer 109, and an n-electrode 140 is formed on the n-type contact layer 104. The translucent thin film p-electrode 110 includes a first layer 111 made of cobalt (Co) having a thickness of about 1.5 nm directly bonded to the p-type contact layer 109 and a gold (Au) having a thickness of about 6 nm bonded to the cobalt film. ) And the second layer 112.

Thick p electrode 120 includes a first layer 121 made of a film thickness of about 18nm of vanadium (V), a film thickness of about _1. A second layer 122 made of 5μm gold (Au), thickness of about 10nm of aluminum ( The third layer 123 made of Al) is sequentially laminated from above the translucent thin film p-electrode 110.

  The n-electrode 140 having a multilayer structure is formed of a first layer 141 made of vanadium (V) having a film thickness of about 18 nm and aluminum (Al) having a film thickness of about 100 nm from above a part of the n-type contact layer 104 that is partially exposed. It is comprised by laminating | stacking the 2nd layer 142 which consists.

A protective film 130 made of a SiO ₂ film is formed on the top.
A reflective metal layer 150 made of aluminum (Al) having a thickness of about 500 nm is formed by metal vapor deposition on the outermost lowermost portion corresponding to the bottom surface of the sapphire substrate 101. The reflective metal layer 150 may be a metal such as Rh, Ti, or W, or a nitride such as TiN or HfN.

With respect to the semiconductor light emitting device 100 described above, the carrier gas for forming the p-type layer 107 made of p-type Al _0.2 Ga _0.8 N was formed with a nitrogen concentration R = 0.4, 0.8, 1 (Ref, comparative example). In forming the other layers, only nitrogen was used. The light intensity of the semiconductor light emitting device 100 was improved by 7% when the nitrogen concentration R = 0.4 and by 15% when the nitrogen concentration R = 0.8 with respect to the nitrogen concentration R = 1 (Ref).

p-Al _0.24 Ga _0.76 N: when forming a Mg layer, graph showing a photoluminescence intensity to nitrogen concentration R in the carrier gas. p-Al _0.24 Ga _0.76 N: when forming a Mg layer, graph chart showing the hole mobility for nitrogen concentration R in the carrier gas. p-Al _0.24 Ga _0.76 N: when forming a Mg layer, graph showing the surface roughness to nitrogen concentration R in the carrier gas. p-Al _0.24 Ga _0.76 N: when forming a Mg layer, graph showing the variation of Al composition on the nitrogen concentration R in the carrier gas. p-Al _0.24 Ga _0.76 N: when forming a Mg layer, graph showing the film thickness variation for the nitrogen concentration R in the carrier gas. Sectional drawing which shows the structure of the semiconductor light-emitting device 100 which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100: Semiconductor light emitting element 101: Sapphire substrate 102: Buffer layer 103: Non-doped GaN layer 104: High carrier concentration n ⁺ layer 105: Multilayer 1061: InGaN well layer 1062: GaN barrier layer 107: p-type AlGaN layer 108: Non-doped AlGaN Layer 109: p-type contact layer 110: translucent thin film p-electrode 120: p-electrode 130: protective film 140: n-electrode 150: reflective metal layer

Claims (2)

In a method for manufacturing a semiconductor light emitting device having a group III nitride compound semiconductor layer containing at least aluminum to which an acceptor impurity is added,
The group III nitride compound semiconductor layer containing at least aluminum to which the acceptor impurity is added is a mixed gas of hydrogen and nitrogen, and the ratio of nitrogen in the mixed gas is 40% to 80%. A method for producing a Group III nitride compound semiconductor light-emitting device, characterized by growing in a gas by metal organic vapor phase epitaxy. 2. The group III nitride compound semiconductor light-emitting element according to claim 1, wherein the group III nitride compound semiconductor layer containing at least aluminum to which the acceptor impurity is added is formed immediately above the light emitting layer. 3. Production method.