JP2006036561A - Method for growing semiconductor crystal, optical semiconductor element, and substrate for crystal growth - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively reduce or minimize the adverse influence of piezoelectric field without derived problems. <P>SOLUTION: An r-plane is grown in parallel to xy-plane on the upper surface of each growing section 4 growing in the non-vertical direction. Each r-plane grows until the stripe groove S is completely covered although each r-plane forms a small void 5 in the vicinity of the side wall surface 1b. Thereby, a nearly successive flat surface is finally formed. At this time, facet growth of the growing section 4 growing in the non-vertical direction is continued for 50 min under following crystal growth conditions; the crystal growth temperature is 990°C, the crystal growth rate in the direction vertical to the r-plane is 0.8 μm/min, and the ratio (V/III) of the flow rate of supplied gases is 5,000. It is important to set the facet growth conditions so as to accelerate continual and favorable facet growth. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for growing a semiconductor crystal and an optical semiconductor device using the semiconductor crystal.
This crystal growth method is very useful for the manufacture of semiconductor light emitting devices and semiconductor light receiving devices (hereinafter collectively referred to as optical semiconductor devices).

  It is generally known that a piezo electric field induced by biaxial strain of an active layer causes a decrease in internal quantum efficiency of a semiconductor light emitting device. As an optical semiconductor device proposed in consideration of such relaxation and minimization of the piezo electric field, for example, one disclosed in Patent Document 1 below is widely known. FIG. 11 and FIG. 12 of the present application are excerpted from Patent Document 1, and show a graph showing the angle dependence of the piezoelectric field in a gallium nitride based semiconductor, and a cross-sectional view of a light emitting device using these semiconductors. ing. The horizontal axis of this graph shows the change of the piezo electric field with respect to the angle θ from the positive direction [0001] of the c axis. From this graph, the magnitude of the piezo electric field in the active layer having the c plane as an interface ( It can be seen that the magnitude (absolute value) of the piezoelectric field is minimum (0 MV / cm) in the active layer having the r-plane, a-plane, or m-plane as the interface.

  And this patent document 1 (2nd Example) states that "First, the n-type GaN contact layer 53 and the n-type AlGaN clad layer 54 are formed on the substrate 51 of SiC, GaN, etc. by the prior art in the {0001} plane direction. Then, a {2-1-14} plane or a {01-12} plane is formed by selective growth or selective etching, and then GaInN / GaN or GaInN / with the plane orientation formed by recrystallization growth. The GaInN multi-strain quantum well layer 55 is formed. Thus, in this Patent Document 1, the configuration and formation of the active layer having a piezoelectric field relaxation effect are described with reference to FIG. A method is disclosed.

Patent Document 2 below describes a crystal growth method using a slope ((1-101) plane) inclined by 62 ° from the c-plane as a crystal growth plane.
JP-A-11-112029 JP 2003-347585 A

However, in the above-mentioned Patent Document 2, an inclination angle of 62 ° is particularly selected with respect to the crystal growth surface. Therefore, as long as this conventional technique is employed, as can be seen from the above graph (FIG. 11), the piezo The electric field cannot be made substantially zero, and therefore the piezo electric field effect still cannot be fully eliminated.
Further, in this Patent Document 2, there is no idea to positively make the piezo electric field substantially zero.

Moreover, in said patent document 1, when performing said selective growth or selective etching, it is difficult to avoid the following problems.
(1) Problems in performing selective growth The formation of an ideal corrugated multi-strain quantum well layer 55 as shown in FIG. 12 by selective growth is in light of the current state of the art regarding crystal growth. It is not always easy. Also, even if such selective growth is possible, we cannot know the method at least from Patent Document 1 described above.

For example, when the above selective growth is performed by forming a large number of striped SiO ₂ masks or the like in the n-type AlGaN cladding layer 54 of FIG. 12, the light being manufactured before and after the mask formation step Since the temperature of the semiconductor element has to be greatly lowered or raised, in this case, stress based on the difference in thermal expansion coefficient between each part is generated in the element. Therefore, in this case, the crystal quality of the well layer stacked thereafter is deteriorated.

Further, even if the thermal expansion coefficient of the substrate or the like is optimally selected by the selection of the substrate material or the like, the crystallinity on the upper exposed surface of the n-type cladding layer is not reduced during the significant temperature increase / decrease as described above. Deteriorated by active atomic desorption phenomenon (sublimation of specific elements) in the vicinity of the exposed surface. Such deterioration of crystallinity is largely based on the etching action by a carrier gas or the like. These circumstances can be easily understood from, for example, the following documents.
(1) Published patent publication: JP-A-11-068159
(2) Published patent publication: JP-A-9-139543
(3) Published patent publication: JP-A-8-88432

In addition, a large number of stripe-like SiO ₂ masks as described above must be disposed and remain in the vicinity of the active layer, which causes a bias (unevenness) in the current density inside the device. Derivative problems such as a decrease in internal quantum efficiency are difficult to avoid. Further, if such a mask is disposed and left in the vicinity of the active layer, there arises a disadvantage that the light extraction efficiency, light capture efficiency, resonance efficiency, etc. of the optical semiconductor element are lowered.

(2) Problems When Performing Selective Etching When performing selective etching, the mask formation process is indispensable, and thus the above-mentioned significant temperature increase / decrease problem is difficult to avoid. Further, if selective etching is performed, damage (surface roughness) associated with the etching process remains remarkably on the eroded surface, so that it is difficult to grow a multiple strain quantum well layer directly on the eroded surface.

  In particular, when forming a laser resonator, in any of the cases (1) and (2), when a corrugated active layer is formed on an optical waveguide, the resonant light is scattered on the inclined surface. Derivation problems such as being easy to be generated occur.

  As described above, it is very difficult to ensure the desired light emission efficiency in the target optical semiconductor element within the technical range that can be specifically known from Patent Document 1 described above. In addition, a report that the light emitting efficiency of the semiconductor light emitting device is actually improved by the concrete device structure as in the above-mentioned Patent Document 1 (FIG. 12) is currently related to the optical semiconductor device related field. Is not found at all. This is thought to be due to the fact that it is difficult to avoid the above problems in actualizing the device structure and manufacturing process of these semiconductor light emitting devices.

  As described above, the piezo electric field generated inside the semiconductor layer such as the active layer is effectively mitigated, or the operating efficiency of the optical semiconductor element can be improved based on those techniques without actually causing a special derivation problem. It is not always easy to improve in light of the current general technical level.

The present invention has been made to solve the above problems, and an object of the present invention is to disclose a method for producing a semiconductor crystal made of a group III nitride compound semiconductor having a large r-plane.
A further object of the present invention is to disclose a structure and a manufacturing method of an optical semiconductor element capable of effectively mitigating or minimizing the adverse effect of a piezoelectric field without causing a special derivation problem.
However, it is sufficient that the above individual objects are achieved individually by at least one of the individual means of the present invention, and the individual invention of the present application (the individual means described below) It does not necessarily guarantee that there is a specific embodiment that solves all of the above problems at the same time.

In order to solve the above problems, the following means are effective.
That is, according to the first means of the present invention, in a crystal growth step of growing a semiconductor crystal made of a group III nitride compound semiconductor on a crystal growth substrate, parallel to each other on the planar main surface of the crystal growth substrate. A groove forming step for forming a plurality of stripe grooves each having a flat inner wall surface, a buffer layer laminating step for laminating a buffer layer on one main inner wall surface of each stripe groove, and each buffer layer A non-longitudinal growth step in which a semiconductor crystal is facet-grown or laterally grown on a crystal growth surface to be provided; and a main growth step in which a semiconductor crystal is grown in a direction perpendicular to the main surface. Of the stripe groove so that θ ₀ −10 ° ≦ θ ₁ ≦ θ ₀ + 10 ° is established with respect to the second angle θ ₀ formed by the c-axis of the semiconductor crystal and the crystal orientation at which the piezoelectric field of the semiconductor crystal becomes zero. Inner wall and main surface It is to set the first angle theta ₁ which forms.

However, it is more desirable to set so as to satisfy “θ ₀ −3 ° ≦ θ ₁ ≦ θ ₀ + 3 °”. Furthermore, it is more desirable to set so as to satisfy “θ ₀ −1 ° <θ ₁ <θ ₀ + 1 °”.

The direction of the c-axis is the direction represented as [0001] if it is written using the Miller index. The Miller index of each crystal plane is exemplified below.
c-plane: (0001)
Side a: (11-20)
m-plane: (10-10)
r-plane: (10-12)
However, these are merely examples, and the crystal structure of the desired semiconductor crystal is a hexagonal system. For example, the a-plane and the m-plane have other five orientation planes that are naturally symmetrical. is there.

  In the above-described main growth step, the semiconductor crystal may be grown in the vertical direction perpendicular to the main surface, or the semiconductor crystal is substantially parallel to the main surface above the mask formed on the main surface. Crystals may be grown laterally. Further, after such a semiconductor crystal is grown in the lateral direction, further vertical growth may be performed. The form of crystal growth related to these growth directions and the combination of each form may be arbitrary.

  Further, the main surface corresponds to a portion called the main surface in the normal crystal growth using a wide single plane for the crystal growth surface (the wide single plane). However, in the present invention, the groove is formed as described above. Since the main surface is processed by introducing a formation process and a buffer layer is stacked in the stripe groove, the main surface does not coincide with a surface on which desired crystal growth is started via the buffer layer.

  In addition, when the cross-sectional shape of the stripe groove is rectangular, the side wall surfaces perpendicular to the main surface (the inner wall surface of the stripe groove) face each other in the stripe groove. The buffer layer may be formed only on one inner wall surface in the groove, and the normal directions of all the inner wall surfaces on which the buffer layer is laminated may be limited to one direction, or alternatively Alternatively, a buffer layer may be formed on both surfaces facing each other.

  When the stripe grooves are filled, local individual crystal growth planes different from the c-plane are connected to each other to form a substantially series of crystal growth planes. Even if voids (: cavities formed without crystal growth) are formed and remain, there is no particular problem.

According to a second means of the present invention, there is provided a crystal growth substrate having a hexagonal crystal structure, wherein the r-axis orientation is selected as the crystal orientation in which the piezoelectric field is zero in the first means. The direction of the normal vector <σ | of the main surface is rotated by the first angle θ ₁ from the positive c-axis direction of the crystal growth substrate toward the positive m-axis direction, and the longitudinal direction of the stripe groove In the direction of the a-axis.

According to a third means of the present invention, there is provided a crystal growth substrate having a hexagonal crystal structure by selecting an r-axis orientation as the crystal orientation in which the piezoelectric field is zero in the first means. The direction of the normal vector <σ | of the main surface is rotated by the first angle θ ₁ from the positive direction of the a-axis to the positive direction of the m-axis from the positive direction of the a-axis of the crystal growth substrate, and the longitudinal direction of the stripe groove In the c-axis direction.

According to a fourth means of the present invention, there is provided a crystal growth substrate having a hexagonal crystal structure by selecting an r-axis orientation as the crystal orientation in which the piezoelectric field is zero in the first means. The direction of the normal vector <σ | of the main surface is rotated by the first angle θ ₁ from the positive direction of the a-axis toward the positive direction of the c-axis from the positive direction of the a-axis of the crystal growth substrate. Is taken in the direction of the m-axis.

  The fifth means of the present invention is to make the crystal orientation in which the piezo electric field becomes zero in the first means as an a-axis or m-axis orientation.

At this time, the second angle θ ₀ is 90 °. Therefore, based on the first means of the present invention described above, if the first angle θ ₁ is in the range of 80 ° or more and 100 ° or less, the effect of suppressing the piezoelectric field is greatly obtained, and the first angle The angle θ ₁ is more desirable as it is closer to a right angle. The crystal growth substrate used at this time is preferably an a-plane substrate having an a-plane as a main surface or an m-plane substrate having an m-plane as a main surface. Further, it is desirable that the longitudinal direction of the stripe groove formed on the main surface is a direction substantially perpendicular to the c-axis direction of the crystal growth substrate. The longitudinal direction of the stripe groove is preferably the m-axis or a-axis direction.

  Further, when the inner side wall (inner wall surface) of the stripe groove is formed from a side wall surface substantially perpendicular to the main surface, when a desired semiconductor crystal is grown in the lateral direction, a buffer layer is formed on the inner side wall on both sides of the stripe groove. It may be formed and then laterally grown and merged at the center of the groove. In such a case, it is desirable to laminate a buffer layer on both of the two side walls (inner wall surfaces) facing each other inside the stripe groove.

  Each of the second to fifth means of the present invention described above exemplifies a more desirable or more specific individual embodiment for carrying out the first means of the present invention. is there. Therefore, these exemplifications do not necessarily mean that any one of the means must be selected and employed when implementing the first means of the present invention. That is, by the first means of the present invention described above, at least any one of the actions / effects described above can be obtained including the actions / effects of the first means of the present invention.

In the case of corresponding to claims 2 to 4, that is, when the r-plane is formed in substantially the same direction as the main surface and the crystal growth surface is further grown, The semiconductor crystal grows at least facet.
Further, in the case of corresponding to claim 5, that is, when the a-plane or m-plane is formed in substantially the same direction as the main surface and the crystal growth surface is further grown, The semiconductor crystal grows at least in the lateral direction.

  According to a sixth means of the present invention, in any one of the first to fifth means described above, the inner wall other than the main inner wall surface constituting the stripe groove is formed before the groove forming step or after the groove forming step. A mask forming step for forming a mask for promoting selective growth of a semiconductor crystal on a wall surface on a crystal growth substrate is provided.

According to a seventh means of the present invention, in the sixth means, each stripe groove is formed so that a flat portion of the main surface remains between other adjacent stripe grooves. In the mask formation process, a mask is also formed on the flat part, and in the main growth process, the semiconductor crystal grown on the stripe groove is used as a nucleus, and the semiconductor crystal is laterally grown on the flat part. .
Note that, after the lateral growth, a desired semiconductor crystal may be grown in the vertical direction.

According to an eighth means of the present invention, in any one of the first to sixth means described above, the plurality of stripe grooves are formed on the main surface without any gap in the width direction. It is to form continuously.
At this time, the flat surface constituting the main surface disappears entirely.

  According to a ninth means of the present invention, in any one of the first to eighth means, an inner wall surface other than the main inner wall surface constituting the stripe groove is formed perpendicular to the main surface. That is.

  According to a tenth means of the present invention, in any one of the first to ninth means, the crystal growth temperature of the semiconductor crystal in the non-longitudinal growth step is set to 900 ° C. or higher and 1150 ° C. or lower. It is.

  The eleventh means of the present invention is the method for growing a semiconductor crystal according to any one of claims 1 to 10, in an optical semiconductor element having a semiconductor layer made of a group III nitride compound semiconductor. And at least a part of the crystal growth substrate or the n-type layer, and at least the lower interface of the active layer is an r-plane, a-plane, or m-plane of the group III nitride compound semiconductor. It is formed from a surface having an off angle within 10 ° with respect to any one surface.

The twelfth means of the present invention is a crystal growth substrate in which a semiconductor crystal made of a group III nitride compound semiconductor is grown on a predetermined base substrate, on a planar main surface of the crystal growth substrate, A plurality of stripe grooves that are parallel to each other and that have a flat inner wall surface are provided, a buffer layer is provided on one main inner wall surface of each stripe groove, and a semiconductor is formed on the crystal growth surface provided by each buffer layer. A non-longitudinal growth portion formed by crystal growth, and θ ₀ −10 ° with respect to a second angle θ ₀ formed by the c-axis of the semiconductor crystal and the crystal orientation at which the piezoelectric field of the semiconductor crystal becomes zero The first angle θ ₁ formed by the main inner wall surface and the main surface of the stripe groove is set so that ≦ θ ₁ ≦ θ ₀ + 10 ° holds.

  The thirteenth means of the present invention is the above-mentioned twelfth means, wherein the upper interface of the non-longitudinal growth portion formed at a position substantially coinciding with the main surface is the r-plane, a-plane, or m-plane. The upper interface is formed in parallel with the main surface, and a series of flat semiconductor crystal layers are stacked on the upper interface.

  By the above means of the present invention, the above-mentioned problem can be effectively or rationally solved.

The effects obtained by the above-described means of the present invention are as follows.
That is, according to the first means of the present invention, a substantially series of vast one r-plane, a-plane, m-plane, or a plane that can be approximated by any one of these planes can be formed by a substantially series of vast layers. A semiconductor crystal having the interface can be manufactured.

  On the crystal growth surface provided by the buffer layer, the target semiconductor crystal usually grows c-plane, so that according to the first means of the present invention, the target semiconductor crystal is subjected to subsequent non-longitudinal growth (facet growth or lateral growth). The r-plane, a-plane, m-plane of the semiconductor crystal, or a plane having an off angle within 10 ° from any one of these crystal planes grows.

Further, based on the relationship of θ ₀ ≈θ ₁ , each crystal growth surface grown in each part grows while facing substantially the same direction as the main surface that the crystal growth substrate originally had. . Hereinafter, crystal growth planes in the same direction are sometimes collectively referred to as Λ planes. The Λ plane is more preferably coincident with any of the r, a, and m planes, but even if it is a plane having a slight (within 10 °) off angle, there is no particular step difference.

Thus, when the above non-vertical growth process is completed, the individual Λ planes of the respective portions are connected to each other in a substantially series to form one large and substantially flat surface.
In addition, even if uneven portions such as slight steps are generated between the individual Λ planes of each part, in the subsequent vertical growth process of the present invention, they are caused by the vertical growth of each part proceeding in the direction perpendicular to the Λ plane. The uneven portions of the surface are corrected well and are sufficiently flattened.

However, it is desirable that the angle θ ₁ is as close to the angle θ ₀ as possible, and the best result is obtained when the angle θ ₁ coincides with the angle θ ₀ . For example, when the target semiconductor crystal is a GaN crystal, the best result is obtained when θ ₁ = 43.2 ° (= θ ₀ ) in order to obtain a series of vast one r-planes.

Further, since this vast layer interface (the above-mentioned Λ plane) is a plane formed based on facet growth or lateral growth, the dislocation density is inevitably suppressed to be low.
Furthermore, the bonding surface between the target semiconductor crystal and the crystal growth substrate is formed in a corrugated plate shape such as a rectangular wave, a triangular wave, or a sawtooth shape. An effect of effectively relieving the stress between the target semiconductor crystal and the crystal growth substrate can be obtained at the same time.

  In addition, the stress relaxation action is more effectively expressed when the voids are formed larger in the stripe grooves. However, the formation of voids in the stripe grooves is not always necessary, and in terms of external quantum efficiency, it is often preferable that the voids be as small as possible or as small as possible. Therefore, regarding the presence or absence of voids in the stripe groove and the size thereof, the conditions such as stress relaxation action and external quantum efficiency, and the performance of the desired optical semiconductor element are also comprehensively considered. In consideration, it is desirable to design each one specifically.

  According to the first means of the present invention for providing each of the functions as described above, it is possible to avoid the generation of atomic detachment that occurs in the above-described temperature increasing / decreasing process, which has been a problem conventionally, or the dislocation density at the interface of the semiconductor crystal Therefore, the crystal quality of the above-described semiconductor crystal can be sufficiently satisfactorily ensured.

  In addition, according to any one of the second to fourth means of the present invention, the stripe groove is formed relatively easily or cleanly on the main surface particularly when a very large r-plane is formed. The buffer layer can be easily, neatly or reliably stacked, or the dislocation density of the target semiconductor crystal can be suppressed to a relatively low level based on the known facet growth effect. it can.

  However, as a standard for determining the direction in which the stripe groove is formed, there may be a viewpoint of the easiness of division when dividing the semiconductor wafer into a desired optical semiconductor element, etc., in addition to the above-mentioned viewpoints of action and effect. . Therefore, it is more desirable to determine the direction in which the stripe grooves are formed in a more comprehensive manner, taking into account the planar shape of the desired optical semiconductor element, for example.

Further, according to the fifth means of the present invention, a vast a-plane or m-plane can be formed.
As a conventional semiconductor light-emitting device in which an active layer is formed on the a-plane or m-plane, for example, the one described in FIG. 18 of “JP 2000-21789” is known. When this optical device is manufactured, at least the active layer and the surrounding semiconductor layer must be crystal-grown under “growth conditions for growing only in the lateral direction”. However, it is actually very difficult to set conditions for crystal growth in the lateral direction in this way. In addition, since the active layer area that can be obtained is not sufficiently large, and the processability of the obtained semiconductor wafer remains a big problem, such optical elements are actually mass-produced. It must be said that it is very difficult in view of the current general industrial technical level.

  However, according to the fifth means of the present invention, a wide a-plane or m-plane can be formed, and the subsequent crystal growth of the desired semiconductor layer is the conventional “growth that grows only in the lateral direction”. It is not necessary to carry out under “conditions”. Therefore, according to the fifth means of the present invention, it is possible to mass-produce light emitting elements and light receiving elements having desired high light emission efficiency and large light output.

  At this time, which crystal plane appears above depends on the orientation of the crystal growth substrate. That is, if a substrate having an a-plane as a main surface is used, a large a-plane can be obtained even for the target semiconductor crystal, and if an m-plane substrate is used, a large m-plane can also be obtained for the target semiconductor crystal. Can do. However, at this time, the longitudinal direction of the stripe groove formed on the main surface is preferably set in a direction substantially perpendicular to the c-axis direction of the crystal growth substrate. More preferably, it is better to take in the m-axis direction or the a-axis direction.

According to the sixth means of the present invention, it is possible or easy to unify the direction of the buffer layer in one way by using a mask that promotes selective growth. For example, when the buffer layer is formed by crystal growth, only the surface in a certain direction where the buffer layer is to be formed may be left and the other surfaces may be masked.
These masks can also act as ELO masks in the vertical growth process. Therefore, in this case, it is possible to effectively reduce the dislocation density of the semiconductor crystal obtained in the vertical growth step of the present invention.

  According to the seventh means of the present invention, the mask formed on the flat part functions as an ELO mask. That is, since a desired semiconductor crystal grows in the lateral direction on this mask, dislocations do not propagate to the laterally grown portion. For this reason, a semiconductor crystal having a low dislocation density can be obtained.

  Further, according to the eighth means of the present invention, since the flat portion does not remain on the main surface, the buffer layer or the substrate can be obtained only by a simple and simple preparation process such as oblique sputtering or oblique exposure. In some cases, only a desired crystal growth surface in a predetermined direction can be formed or exposed. (For example, examples such as FIG. 3-A and FIG. 10-B exemplify such cases typically and specifically.)

According to the ninth means of the present invention, the inner wall surface of the stripe groove can be easily formed by directional dry etching or the like.
Further, according to the ninth means of the present invention, when the fifth means of the present invention is specifically implemented, each inner wall surface of the stripe groove including the main inner wall surface of the stripe groove is formed well. Can do.

  When the cross-sectional shape of the stripe groove is rectangular, the side wall surfaces perpendicular to the main surface (the inner wall surface of the stripe groove) face each other in the stripe groove. The buffer layer may be formed only on one inner wall surface in the groove, and the normal directions of all the inner wall surfaces on which the buffer layer is laminated may be limited to one direction, or alternatively Alternatively, a buffer layer may be formed on both surfaces facing each other. If a buffer layer is formed on both surfaces facing each other, the semiconductor crystals grown from both surfaces can be combined at the approximate center of the stripe groove. Even in such a case, the fifth means of the present invention can be specifically implemented.

  In addition, according to the tenth means of the present invention, the crystal growth conditions that favorably promote facet growth can be set, so that the facet growth on the Λ plane can be continued more reliably in the non-longitudinal growth process. can do. Therefore, according to the seventh means of the present invention, the above series and flattening can be achieved relatively easily and satisfactorily. The preferred value of the crystal growth temperature for the facet growth depends on the flow rate and partial pressure of the carrier gas and the crystal material gas, or the crystal growth rate, but the more preferable crystal growth temperature is usually 950 ° C. to 1100 ° C. It is in the range.

  In addition, according to the eleventh means of the present invention, it is possible to completely eliminate the necessity to intervene the conventional etching process or the conventional mask forming process as seen in the problems of the prior art. Therefore, it is possible to inevitably eliminate the problems caused by the above temperature rise and fall associated with these intervening steps. In addition, since a buffer layer is formed on each of the inner wall surfaces constituting each stripe groove, even if a damage layer is formed on the inner wall surface, the adverse effect is effectively mitigated. Can be suppressed.

  In addition, crystal growth on the Λ plane of each semiconductor crystal layer such as an n-type layer required as an element structure can be started at a stage far before the formation of the active layer. For example, it can be started from an early stage such as performing crystal growth of an n-type contact layer. Furthermore, the crystal growth of the Λ plane makes it possible or easy to form the active layer of the optical semiconductor element into a substantially series of substantially flat plate shapes (planar shapes).

  Therefore, according to the eleventh means of the present invention, it is possible or easy to form an extremely high quality active layer having the Λ plane as an interface by these actions that promote very good crystal growth. Therefore, according to the eleventh means of the present invention, in the target optical semiconductor element, the adverse effect of the piezoelectric field can be effectively mitigated or minimized without causing a special derivation problem. The operating efficiency of the element can be greatly improved.

  In addition, if a crystal growth substrate constructed according to the twelfth means of the present invention is obtained, when producing an optical semiconductor device constructed based on the eleventh means of the present invention, the producer will Therefore, it is not necessary to carry out each manufacturing process requiring a relatively advanced technique such as a groove forming process, a buffer layer laminating process, and a non-longitudinal growth process.

  Therefore, if a crystal growth substrate constructed according to the twelfth means of the present invention is obtained, the above-mentioned optical semiconductor element to be manufactured based on the eleventh means of the present invention can be easily produced by the producer. Can be manufactured. In other words, since the crystal growth substrate constructed according to the twelfth means of the present invention can be extremely useful industrially, the crystal growth substrate of the present invention alone can have high commercial value in the general market.

  In such a crystal growth substrate, it is more desirable to further stack a flat semiconductor crystal layer having an interface parallel to the Λ plane on the Λ plane. That is, according to the thirteenth means of the present invention, the quality of the crystal growth surface is improved by improving the flatness of the crystal growth surface.

  Furthermore, it is possible or easy to remove the base substrate (first crystal growth substrate) by stacking such semiconductor crystal layers sufficiently thick. If the base substrate is removed, the semiconductor crystal layer can be used as a crystal growth substrate made of a self-supporting bulk crystal. A crystal growth substrate made of a self-supporting bulk crystal that does not have a heterogeneous substrate is very advantageous in that it is free from the problem of stress caused by a difference in thermal expansion coefficient or a difference in lattice constant.

Examples of the base substrate (or the first crystal growth substrate) include sapphire, silicon (Si), silicon carbide (SiC), zinc oxide (ZnO), binary, ternary, and quaternary Al _x In _y. Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) or other known substrate materials for crystal growth can be used. That is, these substrates may be cubic crystals and are not necessarily limited to hexagonal crystals.
Further, for example, in order to eliminate stress applied to the semiconductor layer due to a difference in thermal expansion coefficient or a difference in lattice constant, it may be preferable to use a substrate material or the like having a small difference value with respect to a desired semiconductor crystal.

Further, the present invention is based on binary, ternary, or quaternary "Al _1-xy Ga _y In _x N; 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ 1-xy ≦ 1”. This is also effective when a more general group III nitride compound semiconductor is used as a target semiconductor crystal. Further, the above-described target semiconductor crystal is a binary, ternary, or quaternary “Al _1-xy Ga _y In _x N; 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ 1-xy”. ≦ 1 ”, a part of the group III element (Al, In, Ga) is replaced by boron (B), thallium (Tl), or the like, or one of nitrogen (N) in the above composition formula A semiconductor or the like in which a portion is replaced with phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), or the like may be used as the semiconductor crystal for the above purpose. The actions and effects of the present invention show a certain universality even with respect to these slight modifications and substitutions.

  Further, the above-described target semiconductor crystal may be added with a known appropriate impurity of n-type or p-type. As the p-type impurity, for example, magnesium (Mg), calcium (Ca), or the like can be added. As the n-type impurity, for example, silicon (Si), sulfur (S), selenium (Se), tellurium (Te), germanium (Ge), or the like can be added. Further, two or more elements of these impurities may be added simultaneously, or both types (p-type and n-type) may be added simultaneously.

  Further, a substrate removal step of removing the crystal growth substrate from the target semiconductor crystal may be provided after the vertical growth step or in parallel with the vertical growth step. According to the introduction of such a substrate removal process, since the base substrate (first crystal growth substrate) is removed, when the target semiconductor crystal is grown thick, a self-supporting semiconductor bulk crystal can be obtained. Fully possible. Such a self-supporting semiconductor bulk crystal is, of course, useful for a crystal growth substrate of an optical semiconductor element.

  In the case of manufacturing an optical semiconductor element, the lattice constant, thermal expansion coefficient, refractive index, or translucency of the crystal growth substrate is often strictly asked. If it can be removed, it is inevitably freed from such restrictions, so that the material selection of the base substrate is improved.

  Further, depending on the shape and size of the stripe groove, a void is easily formed at the bottom of the stripe groove. Such voids may reduce the light extraction efficiency and light capture efficiency of the optical semiconductor element. Even in such a case, if the base substrate is removed as described above, these voids This problem can be avoided at the same time.

  In order to reduce the probability of breakage of a crystal due to handling of a self-supporting semiconductor bulk crystal and to secure a sufficient yield, the target semiconductor crystal (: self-supporting) The semiconductor bulk crystal) is desirably laminated to at least 400 μm or more. Further, since the buffer layer and the non-longitudinal growth portion are relatively small enough, it is of course possible to obtain substantially the same operation and effect even if these portions are left and only the base substrate is removed. Can do. Alternatively, even if a part of the lower part of the semiconductor crystal layer (the self-supporting semiconductor bulk crystal) is also removed, no particular trouble is caused.

  Further, the substrate removal step can be performed in parallel with the vertical growth step. As a manufacturing method and a manufacturing apparatus that enable such parallel processing, for example, a technique disclosed in, for example, “JP-A 2003-7619: Group III nitride compound semiconductor manufacturing method and manufacturing apparatus” is known. . This known document discloses an apparatus that can simultaneously perform crystal growth, etching, and the like from both the front and back surfaces of a crystal growth substrate. For example, if such a technique is used, the target semiconductor crystal is thickened. When growing, the stress acting on the target semiconductor crystal can be eliminated as much as possible.

  In some cases, the composition of the target semiconductor crystal may be substantially matched with the composition of the crystal growth substrate. As a result, the difference in thermal expansion coefficient between the target semiconductor crystal and the crystal growth substrate can be reduced. Therefore, even when a special apparatus that enables simultaneous processing on both sides as described above cannot be prepared, the stress can be reduced. It is possible or easy to prevent the generation and to form the target semiconductor crystal sufficiently thick.

The depth of the stripe groove is desirably 1 μm or more and 30 μm or less. This range is more desirably 1 μm or more and 15 μm or less. According to such a dimension setting, the Λ planes for crystal growth in each stripe groove are connected well, and a series of substantially flat and vast Λ planes can be formed satisfactorily.
If the depth is too shallow, the stripe groove becomes too thin, and it becomes difficult to form the stripe groove in a desired appropriate shape in view of the processing accuracy of the currently known substrate processing technology. Alternatively, before each beautiful Λ surface is formed in each stripe groove, the individual Λ surfaces may be irregularly connected to each other.

Further, if this depth is excessively increased, the time required for the Λ planes for crystal growth in each stripe groove to be connected to each other well in series (that is, the time required for the non-longitudinal growth step of the present invention) is increased. It is too long to necessarily ensure high productivity. Moreover, if this depth is too deep, the possibility of increasing the level difference between the individual Λ planes, which may occur due to uneven local growth rate, cannot be sufficiently eliminated. If this depth is too deep, the material gas will not easily reach the deep part, especially if the stripe groove has a steep side wall, so depending on the stacking conditions of the buffer layer, etc. Since voids are easily formed, it is not always possible to obtain a desirable crystal growth form in some cases as mentioned above.
From these viewpoints, the depth of each stripe groove is more preferably about 1 μm or more and 15 μm or less. More preferably, the depth of the stripe groove is about 2 μm or more and 5 μm or less.

  Further, when it is desired to obtain a particularly large r-plane, it may be preferable to form one inner wall surface of the stripe groove using a side wall surface substantially perpendicular to the main surface. According to this setting, the side wall surface substantially perpendicular to the main surface can be easily formed by dry etching or the like, and at the same time, when a particularly large r-plane is desired, this configuration allows the stripe groove to be formed. In the above non-longitudinal growth process, there are many cases where the crystal growth conditions such that the grown semiconductor crystal can be filled with almost no excess are easily satisfied. For this reason, it is possible or easy to form an interface with very few voids between the crystal growth substrate and the target semiconductor crystal. Therefore, when the crystal growth substrate is used as it is as a substrate for an optical semiconductor element, an element having high light extraction efficiency or high light extraction efficiency may be manufactured.

Hereinafter, the present invention will be described based on specific examples.
However, the embodiments of the present invention are not limited to the following examples.

(Structure of crystal growth substrate and its manufacturing process)
FIG. 1A shows a side view of the crystal growth substrate 1 (underlying substrate) of Example 1 having a main surface Σ as a main surface. The crystal growth substrate 1 is made of sapphire. The unit vector <σ | in the figure is a normal vector of the substantially flat principal surface Σ above the crystal growth substrate 1, and hereinafter, the direction of the normal vector <σ | is the z-axis of the three-dimensional orthogonal coordinate system. The positive direction of

Further, in this specification, each face of the crystal is distinguished from the above three-dimensional orthogonal coordinate system (x, y, z) by using a Miller index (hkil) in a hexagonal system using four axes. Therefore, for example, the normal vector <σ | described above can be written as the following equation (1) using the three-dimensional orthogonal coordinates.
(Orthogonal coordinate display of normal vector <σ |)
<Σ | = (0, 0, 1) (1)

The crystal growth substrate 1 of FIG. 1-A is formed as a plate-shaped rectangular parallelepiped that satisfies the following formula (2). However, here, a unit vector that faces the positive direction of the c-axis of the sapphire crystal forming the crystal growth substrate 1 of FIG. A unit vector that faces the positive direction of one a-axis of the sapphire crystal is represented by <a |. The angle θ ₀ described below is an angle formed by the c-axis and the r-axis in a hexagonal GaN single crystal (that is, a target semiconductor crystal layer 6 described later), and is 43.2 ° at room temperature.

(Correct coordinate display of unit vectors <c |, <a |)
<C | = (0, sin θ ₀ ′, cos θ ₀ ′),
<A | = (0, cos θ ₀ ′, −sin θ ₀ ′),
θ ₀ ′ ≈θ ₀ (2)
Here, the angle θ ₀ ′ may be a value near the angle θ ₀ , for example, about 45 °. Hereinafter, in this embodiment, it is assumed that θ ₀ ′ = θ ₀ = 43.2 ° is satisfied in this equation (2).

In addition, it should be noted that the main surface Σ is not generally the r-plane even in the case of other than the sapphire substrate. A semiconductor crystal layer having a large parallel r-plane (that is, a target semiconductor crystal layer 6 described later) is obtained. This ideal result depends largely on the angle setting of the inclination angle θ ₁ described later. These points are one of the greatest features of the present invention.

FIG. 1B shows a side view of the crystal growth substrate 1 on which the resist mask 2 is formed on the main surface Σ by coating and baking. FIG. 1C shows a side view of the crystal growth substrate 1 on which the resist mask 2 has been processed. As an exposure method for the resist mask 2, for example, any one of the following methods may be employed. Any appropriate known method can be used for these exposure methods.
(1) A method of creating and using a negative having a stripe-shaped shading pattern (2) A method of irradiating a laser beam whose focus is controlled so as to be adapted to the target shape.

Further, the thickness Δ1 of the resist mask 2 is determined based on the erosion progress speed R in the depth direction of the resist mask 2 at the time of dry etching, the erosion progress speed r of the crystal growth substrate 1, and photolithography. Can be determined on the basis of the inclination angle φ of the inclined surface 2a to be formed, and the inclination angle θ ₁ (FIG. 2) of the inclined surface 1a to be formed on the crystal growth substrate 1 by the subsequent dry etching. The relational expressions to be satisfied by these variables R, r, φ, θ ₁ , Δ1, etc. are already known. For this specific relationship, for example, a relational expression disclosed in JP-A-2001-160657 may be referred to.

FIG. 2 is a perspective view of the crystal growth substrate 1 in which the main surface Σ is processed into a desired shape by the dry etching. The stripe groove S is composed of an inclined surface 1a and a side wall surface 1b in the figure formed on the main surface Σ. Further, symbol Δ2 represents the depth of the stripe groove S, and symbol θ ₁ (= 90 ° −α) represents an angle formed between the main surface Σ of the base substrate 1 and the inclined surface 1a. In this way, when the longitudinal direction of the stripe groove S is substantially coincident with the y-axis direction, the a-axis direction (unit vector <a |) and the longitudinal direction of the stripe groove S ≡ <s | = (0 , 1, 0) is minimal (minimum) (sixth means of the present invention). At this time, as can be seen from the equation (2), ρ = θ ₀ ′.

In Example 1, the crystal growth substrate 1 is formed as shown in the following formula (3).
(Dimensions of base substrate (crystal growth substrate 1))
α ≡ 90 ° −θ ₁ ≒ 47 °,
Δ2 ≒ 3μm,
D ≒ 400μm (3)
The horizontal direction (xy direction) area, aspect ratio, and the like may be arbitrary.

  FIG. 3A is a partial cross-sectional view of the crystal growth substrate 1 showing the buffer layer stacking step of the first embodiment. The buffer layer 3 is a semiconductor layer made of AlGaN (or AlN or GaN) and is formed by sputtering. As a sputtering apparatus to be used, for example, a high-frequency sputtering apparatus or a plasma sputtering apparatus is useful. In this sputtering, a material is sprayed obliquely with respect to the crystal growth substrate 1 at an angle to limit the film formation region (oblique sputtering). The symbol A in the figure represents the projection direction at that time. The tilt angle δ may be about 0 ° to 60 °. A more desirable range in this embodiment is about 3 ° to 10 °. If this angle is large, the void formed later also becomes large. If this angle is too small, the material also adheres to the side wall surface 1b of the crystal growth substrate 1, and the desired r-plane growth in the subsequent non-longitudinal growth process may not progress smoothly.

The conditions for performing the above sputtering are set as follows.
(Sputtering conditions)
Film thickness of AlN to be laminated: 640 [Å]
Sputtering gas: Ar (8 sccm) / N ₂ (10 sccm)
Substrate temperature: 430 [° C]
DC power: 0.5 [W]
Electrode area: 8000 [cm ² ]

  3B and 3C are partial cross-sectional views of the crystal growth substrate 1 showing the subsequent non-longitudinal growth process of the first embodiment. In this non-longitudinal growth step, first, the c-plane of GaN grows on the buffer layer 3. This c-plane growth proceeds as so-called facet growth according to the crystal growth conditions of the following non-vertical growth step, and the normal vector of the upward r-plane on one side of the non-longitudinal growth portion 4 is the first A crystal grows so as to coincide with the normal vector <σ | of the principal surface Σ (FIG. 3-B).

Here, most of each stripe groove S is filled with GaN crystal by MOCVD. Further, H ₂ (or N ₂ ) is used as a carrier gas, and ammonia and trimethyl gallium (TMG) are supplied at the following ratio. As a result, on the upper surface of each non-longitudinal growth portion 4, r-planes grow in parallel with the xy plane as shown in FIG. 3B, and these individual r-planes are slightly adjacent to the side wall surface 1b. While the void 5 is formed, the crystal grows until the stripe groove S is completely covered, and finally, a substantially series of flat surfaces 4a are formed (FIG. 3C).
The specific crystal growth conditions at this time (in FIGS. 3-B and -C) are as follows. This condition setting is important in promoting continuous and steady facet growth. The following crystal growth rate is a crystal growth rate in a direction perpendicular to the r-plane. The following V / III ratio is, of course, a molar ratio.

(Crystal growth conditions of non-longitudinal growth part 4)
Crystal growth temperature: 990 [° C]
Crystal growth rate: 0.8 [μm / min]
Crystal growth time: 50 [min]
Supply gas flow ratio (V / III ratio): 5000

FIG. 4 is a cross-sectional view of a template 10 (new crystal growth substrate) having a target semiconductor crystal layer 6 made of GaN crystals. Here, the crystal growth conditions of the semiconductor crystal layer 6 are as follows.
(Crystal growth conditions of the semiconductor crystal layer 6)
Crystal growth temperature: 1050 [° C.]
Crystal growth rate: 0.6 [μm / min]
Crystal growth time: 100 [min]
Supply gas flow ratio (V / III ratio): 50000

For example, in this way, by slightly changing the crystal growth conditions in the above-described MOCVD method, the dislocation density on the r-plane (upper surface 6a) of the semiconductor crystal layer 6 is suppressed, and the upper surface 6a of the semiconductor crystal layer 6 is further flattened. Can be effectively promoted.
Therefore, since the template 10 obtained as described above promotes the crystal growth of a large and flat active layer having the r-plane as an interface stably and reliably, it is possible to manufacture an optical semiconductor device having a high internal quantum efficiency. It becomes very useful as a crystal growth substrate.
In each example described later, an optical semiconductor element having a high internal quantum efficiency manufactured using such a template will be specifically exemplified.

(Crystal growth conditions for promoting r-plane growth)
For these r-plane growth, the MOCVD method is suitable. Further, the crystal growth conditions for reliably inducing and promoting stable facet growth (r-plane growth) have the following characteristics as compared with the case of normal general c-plane growth.
(1) Crystal growth temperature The crystal growth temperature should be lower than in the case of normal general c-plane growth.

(2) Crystal growth rate The crystal growth rate should be higher than in the case of normal general c-plane growth.
(3) V / III ratio It is better to make the V / III ratio smaller than in the case of normal general c-plane growth.
(4) Ammonia gas supply amount The NH ₃ partial pressure should be higher than that in the case of normal general c-plane growth.

  These specific appropriate ranges are already generally known, and these general trends related to facet growth can be known more specifically from, for example, the following published patent publications. Can do.

  However, the purpose of these prior arts is to improve the crystal quality of the desired semiconductor crystal layer, and these prior art ideas and techniques have a stacked interface consisting of a series of flat and vast r-planes. It does not include the purpose or specific approach of forming a semiconductor crystal layer. In these prior arts, there are many cases where an active layer is formed by c-plane growth, but there are no cases where an active layer is formed by r-plane growth.

(Reference Example 1) Published Patent Publication "JP 10-312971"
(Reference Example 2) Published Patent Publication "JP 11-130597"
(Reference Example 3) Published Patent Publication “JP 11-251631”
Reference Example 4 Published Patent Publication “JP 2001-102307”
(Reference Example 5) Published Patent Publication “JP 2002-280609”
(Reference Example 6) Nobuhiko Sawaki, “Fabrication of GaN microstructures by selective growth-Realization of integrated quantum effect devices-” Meijo University High-Tech Center Symposium (Nitride Semiconductor Research Center Results Presentation Symposium) June 23, 2000 (Reference Example 7) "Transmission Electron Microscopy Investigation of Dislocations in GaN Layer Grown by Facet-Controlled Epitaxial Lateral Overgrowth", JAPANESE
JOURNAL OF APPLIED PHYSICS, Vol.40 (2001) pp.L309-L312, Part2, No.4A, 1 April 2001
(Reference Example 8) Hiromitsu Mizutani and 6 others, “Lower dislocation of GaN by FACELO (facet control ELO)”, IEICE Technical Report, IEICE, ED2000-22, CPM2000-7, SDM2000-22 (2000-05), pp.35-40

(Example of LED configuration)
FIG. 5 is a cross-sectional view of the LED 100 of the second embodiment having the template 10 of the first embodiment. In this template 10, as shown in FIGS. 4 and 5 using the normal vector <σ |, the interface 6a above the semiconductor crystal layer 6 made of non-doped GaN crystal is the r-plane. On the template 10, a high carrier concentration n ⁺ layer 103 made of silicon (Si) -doped GaN with a film thickness of about 4.0 μm is formed. On the high carrier concentration n ⁺ layer 103, a clad layer 104 made of Si-doped n-type GaN and having a thickness of about 0.5 μm is formed.

Further, a light emitting layer 105 having a multiple quantum well structure (MQW) made of GaN and Ga _0.8 In _0.2 N and having a thickness of about 500 mm is formed on the cladding layer 104. On the light emitting layer 105, a clad layer 106 made of p-type Al _0.15 Ga _0.85 N and having a thickness of about 600 mm is formed. Further, a contact layer 107 made of p-type GaN and having a thickness of about 1500 mm is formed on the cladding layer 106.

Further, a thin film positive electrode 110 formed by metal vapor deposition is formed on the contact layer 107, and a negative electrode 140 is formed on the n ⁺ layer 103. The thin film positive electrode 110 includes a thin film positive electrode first layer 111 made of nickel (Ni) having a thickness of about 15 mm bonded to the contact layer 107 and a thin film positive electrode made of gold (Au) having a thickness of about 60 mm bonded to the Ni. The electrode second layer 112 is used.

The thick positive electrode 120 includes a thick positive electrode first layer 121 made of vanadium (V) with a film thickness of about 175 mm, a thick positive electrode second layer 122 made of gold (Au) with a film thickness of about 15000 mm, A thick film positive electrode third layer 123 made of aluminum (Al) having a thickness of about 100 mm is sequentially laminated on the thin film positive electrode 110. The negative electrode 140 includes a vanadium (V) layer 141 having a thickness of about 175 mm, an aluminum (Al) layer 142 having a thickness of about 1000 mm, a vanadium (V) layer 143 having a thickness of about 500 mm, and a nickel having a thickness of about 5000 mm. A (Ni) layer 144 and a gold (Au) layer 145 with a film thickness of 8000 mm are sequentially stacked from above the part of the high carrier concentration n ⁺ layer 103 that is partially exposed. A protective film layer 130 made of a SiO ₂ film is formed on the top.

  In the LED 100 thus formed, the upper and lower interfaces of the active layer (light emitting layer 105) are formed from the r plane, and the piezoelectric field is set to approximately 0 based on this orientation. LED100 shows the luminous efficiency higher than before.

(Configuration example of semiconductor laser)
FIG. 6 shows a cross-sectional view of the semiconductor laser 200 of the third embodiment. This semiconductor laser 200 emits blue-violet light at a peak wavelength of 405 nm, and another template 10 ′ manufactured in substantially the same manner as the template 10 configured based on the base substrate 1 of the first embodiment is used. Have.

  FIG. 7 shows a partial cross-sectional view of the template 10 '. The difference between this template 10 'and the previous template 10 is the cross-sectional shape of the stripe groove S and the projection angle of oblique sputtering. That is, the template 10 'used in the third embodiment employs a V-shaped stripe groove S' having a substantially symmetric cross-sectional shape composed of inclined surfaces 1a and 1b. The buffer layer 3 is the same as FIG. 3A in that the buffer layer 3 is formed only on one inclined surface 1a of the stripe groove, but the angle corresponding to the inclination angle δ at the time of sputtering projection in FIG. Widely taken.

According to such a setting, since the void can be formed relatively large in the template, it is very advantageous in that the stress relaxation action between the base substrate and the semiconductor crystal layer can be effectively obtained.
In the first embodiment described above, one side of the stripe groove is constituted by the side wall surface (1b) substantially perpendicular to the first main surface Σ. However, such a need does not necessarily exist. As illustrated in FIG. 7, a V-shaped groove having a substantially symmetrical cross section, a U-shaped groove, or the like may be formed. In particular, when it is desired to grow a desired semiconductor crystal layer thickly, it is desirable that there is a sufficient strain relaxation effect between the substrate and the growth layer. In such a case, however, the void is rather large. It is desirable to have. In this sense, the cross-sectional shape of the stripe groove is rather desirable to be V-shaped or U-shaped as illustrated in FIG.

  In addition, since the template 10 '(FIG. 7) has a lower portion of the resonator largely etched away as described later, the possibility that the voids adversely affect the external quantum efficiency is at least resonant. The entire area around the vessel is eliminated. Further, since the template 10 'is largely divided into two by this etching (: drilling directly under the resonator), a large strain relaxation effect can be obtained.

A high carrier concentration n-type contact layer 202 made of silicon (Si) -doped GaN and an n-type clad layer 203 made of GaN are sequentially stacked on the template 10 'of FIG. Further thereon, a light emission output section 204 is formed which comprises an active layer and light guide layers of each type located on both upper and lower sides thereof. More specifically, the light emission output unit 204 includes an n-type light guide layer made of Al _0.01 Ga _0.99 N and the activity of a general multiple quantum well (MQW) structure found in a known edge-emitting laser diode. And a p-type light guide layer made of magnesium (Mg) -doped Al _0.01 Ga _0.99 N are sequentially stacked.

A total of two layers, a p-type cladding layer made of p-type Al _0.12 Ga _0.88 N and a p-type contact layer made of Mg-doped p-type GaN, are sequentially stacked on the light emitting output portion 204. A p-type semiconductor layer 205 thus formed is disposed. Most of the n-type contact layer 202 is exposed by etching from above (on the p-type semiconductor layer 205 side), and this etching forms a flat top resonator portion that stands substantially perpendicular to the template 10 '. Is done. In addition, an insulating protective film 210 made of SiO ₂ is formed on both sides of the resonator by sputtering.

  Further, the recess D on the back surface of the template 10 ′ is formed by etching, and the symbol ε represents the remaining film thickness of the n-type contact layer 202 after the formation of the recess D. Thus, the structure in which the thickness ε of the n-type contact layer 202 immediately below the resonator is very thin, for example, about 0.3 μm, is for obtaining a good optical confinement action in the resonator. According to the structure, the occurrence of interference fringes (FFP disturbance) of the n-type contact layer appearing on the emission end face of the resonator can be suppressed extremely effectively.

If all of the n-type contact layer located directly under the resonator is scraped, the current density distribution will be biased, and it will not be possible to efficiently supply current to the resonator. If a part of the n-type contact layer located directly below (for example, ε = 0.3 μm) is left to some extent, a good contact between the negative electrode and the resonator can be secured even directly under the resonator. The current density distribution around the resonator can be maintained in an ideal state, and at the same time, the above-described light confinement action can be secured well. Furthermore, of course, by introducing the template 10 ', the piezo electric field is improved to substantially zero in the active layer of the light emission output unit 204 based on the r-plane growth. Therefore, in the semiconductor laser 200 of the third embodiment, it is effective. It is also possible to suppress the threshold current.
For this reason, the semiconductor laser 200 of the third embodiment oscillates extremely well.

  Further, such a semiconductor laser structure is convenient for accurately controlling the irradiation position (irradiation region) of the laser beam because the FFP in the vertical direction is not disturbed, and has a small spot size with good convergence. It is very useful in realizing a laser.

In the first embodiment, the above-described oblique sputtering is performed. However, the stacking of buffer layers by sputtering may be limited by using a mask.
In Example 1 described above, the buffer layer is formed by sputtering. However, the buffer layer can also be formed by a process such as crystal growth. In this case, a masking process for forming a mask in a portion where the buffer layer is not laminated is required. However, if the buffer layer is formed by crystal growth controlled freely using the mask, the buffer layer Can be formed in a desired area with a substantially uniform thickness and without any unevenness. In addition, it is more desirable to form the buffer layer in such a clean manner in order to ensure higher quality such as flatness of the non-longitudinal growth portion formed in the non-vertical growth step.
In Example 4 below, such a case where a buffer layer is formed by crystal growth will be exemplified.

  8A to 8D are cross-sectional views of the substrate of the example (Example 4) in which the buffer layer is crystal-grown. As the substrate 21, a sapphire substrate is used, and the orientation (orientation) of the substrate 21 is the same as that of the first embodiment (FIG. 1-A). Since the resist mask 22 is made of the same material as that of the resist mask 2 in FIG. 1-B, the variable values of the symbols α, Δ1, and φ are the same as those in the first embodiment.

One of the major features of the fourth embodiment is that a mask 23 made of SiO ₂ is laminated on the main surface Σ of the substrate 21 shown in FIG. Here, the resist mask 22 is formed on the mask 23. According to such a method, as shown in FIG. 8B, an ELO mask (mask 23) that promotes selective growth can be formed on the flat top surfaces of the ridges Rg on both sides where the stripe grooves S are formed.

  The photoresist 24 is formed on the substrate by sputtering or coating. When this photoresist 24 is exposed from the upper right direction A shown in the figure, the photoresist 24 on the mask 23 and the inclined surface 21a can be removed, but the photoresist 24 on the vertical inner wall surface 21b is It remains as it is. Therefore, in the board | substrate 21, only most of the inclined surface 21a is exposed upwards.

FIG. 8D shows the low temperature buffer layer 25 made of AlN or AlGaN stacked on the exposed surface of the inclined surface 21a. Also by such a method, the buffer layer 25 can be laminated in a desired orientation similar to FIG.
Further, according to this method, the lateral growth of the semiconductor crystal is promoted on the mask 23 after the stripe groove S is completely filled with the semiconductor crystal grown thereafter with the low temperature buffer layer 25 as the growth nucleus. Therefore, if the desired semiconductor crystal is grown further upward, the dislocation density of the target semiconductor crystal can be effectively suppressed.

9A, 9B, and 9C are cross-sectional views of the substrate of Example 5 in which the buffer layer is crystal-grown. In the sapphire substrate 31 having the a-plane as the main surface, the longitudinal direction of the stripe groove S is taken on the upper surface, which is the main surface, in a direction perpendicular to the c-axis. The mask 33 made of SiO ₂ is laminated on the main surface and a part of the inner wall surface and the bottom surface of the stripe groove S by oblique sputtering from the upper left direction shown in the figure. By this oblique sputtering, a mask 33 is formed on the substantially vertical inner wall surface 31a and on a portion excluding both the bottom of the stripe groove S having a vertically long cross-sectional shape. The inner wall surface 31a is a sapphire c-plane due to the orientation described above.

  FIG. 9B shows a state in which a low-temperature buffer layer 34 made of AlN or AlGaN is stacked on such a substrate, and a non-longitudinal growth portion 35 made of GaN is facet grown. FIG. 9B shows a state in which the stripe groove S is covered with a GaN crystal forming the non-longitudinal growth portion 35 and a void is formed at the bottom of the stripe groove S and the like. Then, by continuing the growth of the GaN crystal under the crystal growth conditions that promote the a-plane growth, as shown in FIG. 9-C, a desired GaN crystal 36 having a series of large a-plane crystal growth surfaces is obtained. Obtainable.

  10A and 10B are both cross-sectional views of the substrate of Example 6 in which the buffer layer is crystal-grown. As for the orientation of the sapphire substrate 41 in this figure, the vertical upward direction coincides with the m-axis direction, and the horizontal right direction coincides with the c-axis direction. Therefore, the vertical inner wall surface 41a of the stripe groove S is a sapphire c surface. A photoresist 42 was formed by coating or sputtering from above the sapphire substrate 41 having such a deep substantially V-shaped stripe groove S (FIG. 10A).

  The direction of the arrow shown in FIG. 10A indicates the exposure condition for this photoresist 42. That is, the exposure is performed from the upper right direction so that only the upper part of the inner wall surface 41a is exposed. Even with such a configuration, only the sapphire c-plane can be exposed. In this case, too, a series of vast m-planes are crystallized according to the crystal growth process substantially the same as in FIGS. 9-B and 9-C. A desired semiconductor crystal made of GaN can be obtained as a growth surface.

[Other variations]
The embodiment of the present invention is not limited to the above-described embodiment, and other modifications as exemplified below may be made. Even with such modifications and applications, the effects of the present invention can be obtained based on the functions of the present invention.

(Modification 1)
For example, when a large void is formed, the above stress generated between the substrate and the growth layer due to a difference in thermal expansion coefficient or a difference in lattice constant is the shear stress applied to the non-longitudinal growth portion or the protrusion of the base substrate. In some cases, the base substrate can be separated cleanly. That is, there are cases where such a shearing action may be used. As for such a separation process and separation action, there is a similar example related to, for example, published patent publication “Japanese Patent Laid-Open No. 2002-293698: Semiconductor substrate manufacturing method and semiconductor element”. Introducing the crystal growth method of the invention can be a very useful technique.

(Modification 2)
Further, in the above-described Example 2 and Example 3, the base substrate (crystal growth substrate 1) is not removed but left in the semiconductor light emitting device (100, 200). For example, the semiconductor crystal layer 6 of FIG. If the thickness is laminated to 400 μm or more, for example, the semiconductor crystal layer 6 becomes stable as a free-standing single bulk crystal. Therefore, a desired optical semiconductor element is manufactured using such a bulk crystal as a new crystal growth substrate. Also good. In such a case, for example, the void 5 formed between the non-longitudinal growth portion 4 and the base substrate (crystal growth substrate 1) in FIG. 4 is completely formed in a later step (the aforementioned substrate removal step). Since it can be eliminated, the above-mentioned problem that such a void lowers the external quantum efficiency of the optical semiconductor element can inevitably be solved.

Further, when the base substrate is separated or removed later in this way, a larger void formed during the manufacturing process is more desirable because it provides a stress relaxation action. Moreover, when manufacturing such a self-supporting single bulk crystal, as mentioned above, the purpose is after the above-described vertical growth process or in parallel with the vertical growth process. A substrate removal step for removing the crystal growth substrate from the semiconductor crystal may be provided.
On the other hand, the stress relief action due to the uneven structure or void formed between the crystal growth substrate (underlying substrate) and the semiconductor crystal based on the formation of a large number of stripe grooves without using such a technique. If it is scarce, it should be noted that a desired semiconductor crystal layer may be deposited only about 10 μm.

(Modification 3)
In the first embodiment, the depth and the formation cycle of the stripe grooves are unified to be substantially constant. However, it is not always necessary to form the stripe grooves in a unified form. What is most important here is that the ridge-like vertex lines are arranged substantially in parallel on the substantially same plane (Σ), and the inclination angle θ ₁ of each inclined surface (1a) is the angle θ ₀ described above. To approximately match.
Further, the width of the stripe groove is not necessarily constant as shown in FIG. This is also true for the x-axis direction, the y-axis direction, and even the z-axis direction in FIG.

In the first embodiment, the main surface Σ of the first crystal growth substrate (underlying substrate) is almost completely removed, but the upper main surface (Σ) is partially and discretely formed in the undersubstrate. You may leave some.
For example, when silicon (Si) is used as the base substrate, GaN grows on the crystal growth surface provided by the buffer layer, but is difficult to grow directly on the base substrate (Si). Even if the original upper main surface partially and discretely remains after the stripe grooves are formed on each other, if the width is narrow within about several μm, each crystal growth surface becomes one substantially flat surface. It is sufficiently possible to connect to the surface without any particular inconvenience, and no other derivation problems arise. In this sense, it is considered effective to use silicon (Si) as the base substrate.

(Modification 4)
Further, as described in the above-mentioned published patent publication “Japanese Patent Laid-Open No. 2002-293698: Semiconductor substrate manufacturing method and semiconductor element”, when silicon (Si) is used as a base substrate, silicon carbide (SiC) is used. If a well-known reaction prevention layer made up of, for example, is formed, the number of lamination steps increases, but it may be more effective with respect to crystal quality and the like.
Further, since silicon (Si) is a relatively soft material, it is advantageous from the viewpoint of strain relaxation action and etching ease. In the first embodiment, the stripe grooves are formed by dry etching. However, wet etching may be performed depending on individual conditions such as a substrate material.

  The crystal growth method of the present invention and the crystal growth substrate of the present invention are very useful for the production of semiconductor light emitting devices such as LEDs and semiconductor lasers and semiconductor light receiving devices. In addition, these crystal growth methods and optical semiconductor devices manufactured using the crystal growth substrate of the present invention are also within the scope of the present invention.

Side view of crystal growth substrate 1 (underlying substrate) of Example 1 having main surface Σ as the main surface Side view of crystal growth substrate 1 with resist mask 2 formed on main surface Σ Side view of crystal growth substrate 1 in which resist mask 2 is shaped Perspective view of crystal growth substrate 1 whose main surface Σ has been processed by dry etching Partial sectional view of the crystal growth substrate 1 showing the buffer layer stacking step of Example 1 Partial sectional view of the crystal growth substrate 1 showing the non-longitudinal growth step (first half) Partial sectional view of the crystal growth substrate 1 showing the non-longitudinal growth step (second half) Sectional view of template 10 having target semiconductor crystal layer 6 Sectional drawing of LED100 which has the template 10 (Example 2) Sectional view of semiconductor laser 200 having template 10 '(Example 3) Partial sectional view of template 10 '(Example 3) Sectional view of substrate of Example (Example 4) for crystal growth of buffer layer Sectional view of substrate of Example (Example 4) for crystal growth of buffer layer Sectional view of substrate of Example (Example 4) for crystal growth of buffer layer Sectional view of substrate of Example (Example 4) for crystal growth of buffer layer Sectional view of substrate of Example (Example 5) for crystal growth of buffer layer Sectional view of substrate of Example (Example 5) for crystal growth of buffer layer Sectional view of substrate of Example (Example 5) for crystal growth of buffer layer Sectional view of substrate of Example (Example 6) for crystal growth of buffer layer Sectional view of substrate of Example (Example 6) for crystal growth of buffer layer Graph showing angle dependence of piezoelectric field in gallium nitride semiconductors Sectional view of a conventional optical semiconductor device that attempted to relax the piezoelectric field in the active layer

Explanation of symbols

1: Crystal growth substrate (underlying substrate)
1a: Inclined surface of base substrate (crystal growth substrate 1) 1b: Side wall surface of base substrate (crystal growth substrate 1) S: Striped groove (consisting of inclined surface 1a and side wall surface 1b)
2: Resist mask 3: Buffer layer 4: Non-longitudinal growth part 5: Void 6: Target semiconductor crystal layer 10: Template (new crystal growth substrate obtained in Example 1)
10 ': Template (Example 3)
100: LED of Example 2
200: Semiconductor laser of Example 3 θ ₀ : Angle formed by c-plane and r-plane of target semiconductor crystal (semiconductor crystal layer 6) θ ₁ : Angle formed by main surface Σ of base substrate 1 and inclined surface 1a φ : Inclination angle of resist mask 2 Σ: Main surface (main surface) above base substrate (crystal growth substrate 1)
<Σ |: Normal vector of principal surface Σ <c |: Direction vector of c-axis <a |: Direction vector of a-axis

Claims (13)

A method of growing a semiconductor crystal made of a group III nitride compound semiconductor on a crystal growth substrate,
A groove forming step of forming a plurality of stripe grooves parallel to each other and having a flat inner wall surface on a planar main surface of the crystal growth substrate;
A buffer layer laminating step of laminating a buffer layer on one main inner wall surface of the stripe groove;
A non-longitudinal growth step of facet growing or laterally growing the semiconductor crystal on a crystal growth surface provided by the buffer layer;
A main growth step for crystal growth of the semiconductor crystal in a direction perpendicular to the main surface;
A first angle θ ₁ formed by the main inner wall surface of the stripe groove and the main surface is a second angle θ formed by the c-axis of the semiconductor crystal and the crystal orientation at which the piezoelectric field of the semiconductor crystal becomes zero. against _0, the crystal growth method of the semiconductor crystal and satisfies the _{θ 0 -10 ° ≦ θ 1 ≦} θ 0 + 10 °. The crystal orientation at which the piezoelectric field is zero is the r-axis orientation,
The crystal growth substrate is
Having a hexagonal crystal structure,
The direction of the normal vector <σ |
The crystal growth substrate rotates from the positive direction of the c-axis toward the positive direction of the m-axis by the first angle θ ₁ .
The longitudinal direction of the stripe groove is
2. The crystal growth method for a semiconductor crystal according to claim 1, wherein the crystal growth method is in the direction of the a-axis. The crystal orientation at which the piezoelectric field is zero is the r-axis orientation,
The crystal growth substrate is
Having a hexagonal crystal structure,
The direction of the normal vector <σ |
The crystal growth substrate rotates from the positive direction of the a-axis toward the positive direction of the m-axis by the first angle θ ₁ ;
The longitudinal direction of the stripe groove is
2. The crystal growth method for a semiconductor crystal according to claim 1, wherein the crystal growth method is in the direction of the c-axis. The crystal orientation at which the piezoelectric field is zero is the r-axis orientation,
The crystal growth substrate is
Having a hexagonal crystal structure,
The direction of the normal vector <σ |
The crystal growth substrate rotates from the positive direction of the a-axis toward the positive direction of the c-axis by the first angle θ ₁ .
The longitudinal direction of the stripe groove is
The method of growing a semiconductor crystal according to claim 1, wherein the crystal growth method is in the direction of the m-axis. The crystal orientation in which the piezoelectric field is zero is
The crystal growth method for a semiconductor crystal according to claim 1, wherein the crystal growth method is an a-axis or m-axis orientation. Before the groove forming step or after the groove forming step,
2. A mask forming step of forming a mask for promoting selective growth of the semiconductor crystal on the crystal growth substrate on an inner wall surface other than the main inner wall surface constituting the stripe groove. 6. The method for growing a semiconductor crystal according to any one of 5 above. The stripe groove is
It is formed so that the flat portion of the main surface remains between the adjacent other stripe grooves,
The mask forming step includes
A step of forming a mask on the flat portion,
The growth process includes
The method of growing a semiconductor crystal according to claim 6, further comprising a step of laterally growing the semiconductor crystal on the flat portion using the semiconductor crystal grown on the stripe groove as a nucleus. The plurality of stripe grooves are
7. The crystal growth method for a semiconductor crystal according to claim 1, wherein the crystal growth method is continuously formed on the main surface without any gap in the width direction. . The crystal growth of a semiconductor crystal according to any one of claims 1 to 8, wherein an inner wall surface other than the main inner wall surface constituting the stripe groove is formed perpendicular to the main surface. Method. The crystal growth temperature of the semiconductor crystal in the non-longitudinal growth step is:
The method of growing a semiconductor crystal according to any one of claims 1 to 9, wherein the temperature is 900 ° C or higher and 1150 ° C or lower. An optical semiconductor element having a semiconductor layer made of a group III nitride compound semiconductor,
The semiconductor crystal manufactured based on the crystal growth method of a semiconductor crystal according to any one of claims 1 to 10 is included in at least a part of a crystal growth substrate or an n-type layer,
At least the lower interface of the active layer
With respect to any one of the r-plane, a-plane, and m-plane of the group III nitride compound semiconductor,
An optical semiconductor element characterized by being formed from a surface having an off angle of 10 ° or less. A crystal growth substrate in which a semiconductor crystal made of a group III nitride compound semiconductor is grown on a predetermined base substrate,
On the planar main surface of the crystal growth substrate, there are a plurality of stripe grooves which are parallel to each other and whose inner wall surface is a plane,
On one main inner wall surface of each stripe groove, each has a buffer layer,
Each of the buffer layers provided on the crystal growth surface has a non-longitudinal growth portion formed by the growth of the semiconductor crystal,
A first angle θ ₁ formed by the main inner wall surface of the stripe groove and the main surface is a second angle θ formed by the c-axis of the semiconductor crystal and the crystal orientation at which the piezoelectric field of the semiconductor crystal becomes zero. against _0, the crystal growth substrate characterized by satisfying the _{θ 0 -10 ° ≦ θ 1 ≦} θ 0 + 10 °. The upper interface of the non-longitudinal growth portion formed at a position substantially coinciding with the main surface is:
It is formed from any one of r-plane, a-plane, or m-plane,
The upper interface is
Formed parallel to the main surface,
On the upper interface,
The crystal growth substrate according to claim 12, wherein a series of flat semiconductor crystal layers are stacked.

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