JP5115925B2 - Microcrystalline nitride semiconductor optical / electronic devices with controlled crystal orientation and facets - Google Patents

Description

  The present invention relates to a semiconductor electronic device having a polycrystalline / microcrystalline structure.

  The semiconductor electronic device is a light emitting diode (hereinafter referred to as “LED”) having a double heterojunction such as a pn junction or a pin, a light receiving device such as a solar cell or a photosensor, an electron emitting device used for a display, etc. A semiconductor element that emits and absorbs.

  In recent years, ultraviolet, blue, and green light emitting diodes using nitride semiconductors and white light emitting diodes that combine phosphors have already been put into practical use.

  In particular, white light emitting diodes are attracting attention as the fourth lighting alternative to current fluorescent lamps. In recent years, there have been reports that characteristics such as luminous efficiency are equal to or higher than fluorescent lamps (> 150lm / W). ing.

  The market for white light emitting diodes is expected to grow significantly in 2015, and is expected to reach 650 billion yen in 2015. Considering these points, cost reduction of the current nitride-based light emitting diode is a very important issue. It is also important to fabricate on a larger substrate when considering application to displays and the like. The current nitride semiconductor light-emitting diodes are grown on a sapphire substrate, and the price of this substrate is about 10,000 yen for a 2-inch size, and it is difficult to increase the area of the sapphire substrate. And application problems.

  As one of methods for solving these problems, it is conceivable to use an amorphous substrate such as a glass substrate and a polycrystalline nitride semiconductor substrate which are cheaper and can easily be enlarged. In fact, the following patent document discloses a technique related to a nitride semiconductor optical device using a polycrystalline / amorphous substrate as a large-area and inexpensive substrate instead of a sapphire single crystal substrate.

JP 2000-133841 A

  In the technique of Patent Document 1, a polycrystalline gallium nitride (hereinafter referred to as GaN) light emitting diode is manufactured on a quartz substrate. However, it has been reported that the emission intensity of this polycrystalline light emitting diode is 100 times weaker than that of a single crystal light emitting diode.

  The main cause of the characteristic deterioration in such a polycrystalline light emitting diode is a difference in crystal quality from the single crystal. In Patent Document 1, a device such as depositing a low-temperature GaN relaxation layer is devised to try to obtain a structure and characteristics as close as possible to a single crystal light emitting diode. However, since a polycrystalline structure usually has a larger number of crystal grain boundaries than a single crystal, defects such as dislocations present at the grain boundaries become non-light emitting centers, and the luminous efficiency is greatly reduced.

  For these reasons, a conventional light emitting diode on a polycrystalline substrate is inefficient even if the cost can be reduced, and it is very difficult to realize a low cost and highly efficient polycrystalline light emitting diode.

  That is, in order to realize an optical element such as a high-efficiency light-emitting diode based on a polycrystalline structure, it is necessary to reduce non-radiative recombination that occurs at a crystal grain boundary and achieve high efficiency. For that purpose, it is indispensable to develop a new device structure and its growth method that make use of the characteristics of the polycrystalline structure, rather than simply creating a structure similar to the device structure on a single crystal on an amorphous substrate or a polycrystalline substrate. It is.

  In view of the circumstances described above, an object of the present invention is to provide a novel high-efficiency optical device structure and a method for manufacturing the same using a polycrystalline nitride semiconductor substrate that is inexpensive and easy to increase in area.

  The present invention is based on a polycrystalline or microcrystalline nitride semiconductor (hereinafter simply referred to as polycrystalline nitride semiconductor) composed of crystal grains having different crystal faces (facets), and the facets of each crystal grain are random. It is a semiconductor electronic device that is used or whose structure is controlled.

The polycrystalline nitride semiconductor described here is characterized in that the average diameter of each crystal grain contained in the semiconductor is 1 mm or longer, which is sufficiently longer than the minority carrier diffusion length (several tens of nm) in the GaN crystal. For example, in an image of 100 mm ² or more of an electron / optical microscope, it is formed from two or more crystal grains / microcrystals having different crystal orientations, and the standard deviation of the area of each crystal grain / microcrystal is at least 1 mm ² or more. It means a polycrystalline nitride semiconductor characterized by

  By controlling the crystal axis orientation, facet shape, size, and mixed crystal composition of each crystallite or its crystal grains, and simultaneously proceeding with different crystal production processes on different crystal faces, the characteristics of each crystal face can be adjusted. This is a semiconductor optical device capable of controlling the emission wavelength including white using the difference.

  If these polycrystalline and microcrystalline semiconductors are formed using InGaN or AlGaN mixed crystals, the layer thickness and mixed crystal composition show non-uniformity due to the difference in the mixed crystal growth process for each crystal grain, A semiconductor optical element that can be applied as a new white light source that does not require a phosphor or the like can be formed, and a white light device can be formed by a completely new inexpensive and simple method.

  A polycrystalline nitride semiconductor is a semiconductor electronic device characterized by diffracting from two or more different crystal plane orientations in a 2θ / θ scan of X-ray diffraction measurement.

  As a substrate material for a polycrystalline nitride semiconductor element, a low-cost polycrystalline material that is transparent in the ultraviolet, visible, and near-infrared wavelength region is suitable, but any material such as a single crystal substrate or a cheaper amorphous substrate can be used. It can be used and is not limited to a polycrystalline substrate.

  A polycrystalline nitride semiconductor optical device according to one means of the present invention is formed by using a polycrystalline structure having the above characteristics as a base, an active layer including a first quantum well structure, and further sandwiching the active layer. A second n-type semiconductor clad layer, a third p-type clad layer, a pair of contact layers connected to each, a first electrode and a second electrode connected to each of the contact layers, It is also preferable to have

  In each of the above means, the first polycrystalline semiconductor layer is expressed by the formula InxGa1-xN (0 <x <1) or AlyGa1-z-yInzN (0 <y <1, 0 <z <1). It is formed of a crystalline nitride semiconductor.

  The second n-type cladding layer is a layer formed for injecting and confining electron carriers in the polycrystalline active layer, and is not limited to, for example, GaN, InGaN mixed crystal or AlGaN mixed crystal polycrystalline Si. A layer in which, for example, impurities are implanted can be preferably used.

  The third p-type cladding layer is a layer formed for injecting and confining hole carriers in the polycrystalline active layer, and is not limited to, for example, GaN, InGaN mixed crystal or AlGaN mixed crystal polycrystalline. A layer in which Mg or the like is implanted as an impurity can be preferably used.

  As described above, according to the present invention, a novel polycrystalline semiconductor optical device can be provided.

  The inventors of the present invention have come up with the idea that new optoelectronic devices can be developed that make use of the unique features of polycrystalline materials by using polycrystalline semiconductors that are inexpensive and easy to increase in area, and by actively using different crystal planes. Thus, the present invention has been completed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention can be expressed as many different embodiments and examples, and needless to say, the present invention is not limited to the embodiments and examples.

(Embodiment 1)
FIG. 1 is a surface electron microscope image (SEM: 40 × 30 mm ² image) of a nitride polycrystalline semiconductor according to the present embodiment. At the same time, the results of crystal orientation analysis of each crystal grain obtained by back electron diffraction image (EBSP) are also shown. By comparing the results of SEM and EBSP, the polycrystalline semiconductor according to the present embodiment is a polycrystalline body having various crystal orientations, and the crystal orientations are aligned within each crystal grain. The crystal quality is considered to be relatively high. This polycrystal has a relatively large crystal grain (the standard deviation of the average grain area in this case is 40 mm ² ), and this crystal grain area is sufficiently larger than the minority carrier diffusion length (several tens nm) in the GaN crystal Therefore, the influence of the crystal grain boundary is small, and there is a high possibility that high-efficiency light emission can be obtained from the randomly oriented crystal grains. Most of the researches on polycrystalline semiconductors reported to date have been based on the idea of how close to the crystallinity of single crystal semiconductors, but in the present invention, random crystal orientation of polycrystalline / microcrystalline structures It is characterized by actively using.

  FIG. 2 is a schematic view of a polycrystalline light emitting diode (LED) structure according to this embodiment. The LED according to this embodiment includes a substrate 1, a low-temperature relaxation layer 2, an n-type contact layer 3, an n-type cladding layer 4, an active layer 5, a p-type cladding layer 6, and a p-type contact layer 7 stacked in this order. ing. A first electrode 8 is formed on the n-type contact layer 3, and a second electrode 9 is formed on the p-type contact layer 7. A voltage is applied between the first and second electrodes. Thus, holes and electrons can be injected into the active layer 5 to emit light.

The substrate 1 is used for growing each polycrystalline layer such as GaN formed thereon, and has a crystal grain area sufficiently larger than the minority carrier diffusion length (several tens of nm) in the GaN crystal. It is used for growing a polycrystalline layer. Although not limited, for example, an AlN or GaN polycrystalline nitride semiconductor substrate, a sapphire substrate, a SiC substrate, an amorphous substrate such as glass, or a metal substrate can be used as the substrate. Here, the polycrystalline layer having sufficiently large crystal grains is formed of, for example, two or more crystal grains / microcrystals having different crystal orientations in an electron microscope and an optical microscope image (size of 100 mm ² or more), The standard deviation of the area of crystal grains / microcrystals is at least 1 mm ² or more.

  The low-temperature relaxation layer 2 is a layer for improving the coverage and flatness of the polycrystalline layer grown on the substrate 1, and is a layer for growing the polycrystalline layer having the above crystal grain size. Although not necessarily, a GaN polycrystal, an AlGaN mixed crystal, or an InGaN mixed crystal low-temperature relaxation layer can be suitably used.

The low-temperature relaxation layer 2 can also be used for film coating and subsequent crystallization / crystal grain increase. For example, an amorphous substrate such as glass can be used as the substrate 1 in this embodiment. In this case, first, after depositing a low-temperature relaxation layer, the substrate temperature is raised to an appropriate temperature to crystallize the crystal grains. It is possible to grow a polycrystalline structure having a plurality of crystal grains with an area of 1 mm ² or larger.

  The n-type contact layer 3 is a layer formed for electrical connection with the n-type clad layer 4, and is not limited to, for example, GaN polycrystal, InGaN mixed crystal, AlGaN mixed crystal polycrystal, Si, etc. A layer in which is implanted as an impurity can be preferably used.

  The n-type cladding layer 4 is for injecting electrons into the active layer 5 and is not limited to, for example, implanting Si or the like as an impurity into GaN polycrystal, AlGaN mixed crystal or InGaN mixed crystal polycrystal. The layer thus obtained can be suitably used.

Since the active layer 5 is formed on the substrate 1, the contact layer 2, and the clad layer 3, it has a randomly oriented polycrystalline nitride semiconductor structure. In the polycrystalline semiconductor devices reported so far, efforts have been made to make the polycrystalline structure as close as possible to the single crystal structure, but in this embodiment, the randomly oriented crystal grains are actively used. This indicates that new functions can be expressed. For example, “K. Nisizuka et. Al.,
Appl. Phys. Lett., 85, 3122 (2004) ”, in the quantum well structure using InGaN mixed crystal as the active layer, its In composition and InGaN well layer thickness depend on the crystal orientation of the underlying layer. Light with different emission wavelengths is detected from around 450 nm, which is emitted from the (0001), (11-22), and (11-20) planes, and contains In composition and InGaN for each crystal orientation. This is probably because the crystal composition is different, that is, if various crystal orientations are created and an InGaN mixed crystal is grown, the In composition may be controlled at random. In this way, a completely new white LED can be realized by a fundamentally different method from white LEDs manufactured using phosphors.

  However, in the technique described in the above document, the growth is performed on single crystal sapphire, and the LED structure itself is also a single crystal. Therefore, unless special processing is performed, single crystal structures having various crystal orientations are realized. This is difficult, and the cost is much higher than the white LED based on the conventional phosphor + ultraviolet LED. In this embodiment, since a polycrystalline semiconductor is originally used as a base, it is easy to form an active layer having a random crystal orientation. Moreover, since it can be produced without using an expensive substrate such as sapphire, it is far superior to the conventional white LED in terms of cost.

  The active layer 5 according to the present embodiment is made of, for example, InGaN mixed crystal polycrystal, and the In composition incorporation process and the growth rate of the InGaN mixed crystal are different for each randomly oriented crystal grain. It is thought to have. By actively utilizing and controlling these orientations and the randomness of the In composition of each InGaN polycrystalline grain, we can expect a completely new white LED structure that does not use phosphors.

  The p-type cladding layer 6 is used for injecting holes into the polycrystalline active layer 5, and this layer is not limited to, for example, GaN polycrystalline or AlGaN mixed crystal, InGaN mixed crystal. A layer in which Mg or the like is implanted as an impurity in the polycrystal can be preferably used.

  The p-type contact layer 7 is used for injecting holes into the active layer 5, and is not limited to, for example, GaN polycrystal, InGaN mixed crystal, AlGaN mixed crystal polycrystalline material such as Mg. A layer implanted as an impurity can be preferably used.

  The first electrode 8 is used for injecting electrons into the active layer 5 and is not limited as long as it has conductivity. For example, aluminum (Al), titanium (Ti), gold An electrode layer composed of (Au) or the like can be suitably used.

  The second electrode 9 is used for injecting holes into the active layer 5 and is not limited as long as it has conductivity. For example, palladium (Pd), nickel (Ni), An electrode layer made of gold (Au) or the like can be preferably used.

  As described above, the polycrystalline LED according to this embodiment emits light when a voltage is applied between the first electrode and the second electrode and electrons and holes are injected into the active layer 5.

  The optical element based on a polycrystalline semiconductor according to the present invention can be an industrially important element in drastically reducing the cost and increasing the area of the current white LED. Furthermore, since it can have a wide light emission and light reception wavelength in the visible light region, it can be used for an inexpensive and highly efficient solar cell.

  Here, the manufacturing method of the polycrystalline LED according to this embodiment will be described. The LED manufacturing method according to this embodiment includes a step of forming a low-temperature relaxation layer 2 on a substrate 1, a step of forming an n-type contact layer 3, a step of forming an n-type cladding layer 4, and a step of forming an active layer 5. , A step of forming the p-type cladding layer 6, a step of forming the p-type contact layer 7, a step of forming the first electrode 8, and a step of forming the second electrode 9.

  The polycrystalline LED structure is not limited, and for example, metal organic chemical vapor deposition, MBE, or pulsed laser deposition can be used.

The substrate 1 is used to grow each polycrystalline layer such as GaN formed thereon, and has a crystal grain area sufficiently larger than the minority carrier diffusion length (several tens of nm) in the GaN crystal. It is used for growing a polycrystalline layer. Although not limited, for example, GaN, AlN polycrystalline nitride semiconductor substrate, sapphire substrate, SiC substrate, amorphous substrate such as glass, or metal substrate can be used as the substrate. Here, a polycrystalline layer having sufficiently large crystal grains is formed from, for example, two or more crystal grains / microcrystals having different crystal orientations in an electron microscope image or an optical microscope image (image size of 100 mm ² or more). The standard deviation of the area of each crystal grain / microcrystal is 1 mm ² or more.

  Since the coverage and flatness of the polycrystalline semiconductor differ depending on the substrate 1, the low-temperature relaxation layer 2 can be used to improve the coverage and flatness. The low temperature relaxation layer is not limited, but is formed of polycrystalline AlN, GaN, InN, or a mixed crystal thereof. The growth temperature grows at a low temperature of about 550 ° C., for example.

  The step of forming the n-type contact layer 2 on the substrate 1 can be omitted when a conductive polycrystalline semiconductor substrate, metal substrate, amorphous substrate, or single crystal substrate is used as the substrate 1.

  The substrate temperature when forming the n-type cladding layer 3 varies depending on the material of the layer to be formed and can be adjusted as appropriate. It is. The thickness is about several μm.

The active layer 5 is made of, for example, InGaN mixed crystal polycrystal, and it is considered that each of the crystal grains has a different emission wavelength because the incorporation process of the In composition and the growth rate of the InGaN mixed crystal are different for each randomly oriented crystal grain. . The growth temperature is, for example, in the range of 600 ° C. to 800 ° C., and the thickness of the InGaN polycrystalline active layer is 10 to 100 nm or less. InGaN mixed crystal grows with the information of each underlying crystal grain tightly, and since the crystal orientation differs for each crystal grain, the growth rate and the incorporation rate of In raw material are different. As a result, InGaN crystal grains having different In compositions with X _In = 0 to 0.5 can be easily formed by randomly formed crystal grains, and the randomness of the In composition of these InGaN polycrystal grains is positive. By using and controlling them, it is expected to realize a completely new white LED structure that does not use phosphors.

  The process of forming the p-type cladding layer 6 and the p-type contact layer 7 can employ substantially the same process as the process of forming the n-type cladding layer 4 except for the material.

The step of forming the first electrode 8 is not limited, but can be formed by vacuum deposition. Since the first electrode 9 is formed on the n-type contact layer 2, it is preferable to form the first electrode 9 after exposing the n-type contact layer 2 using, for example, photolithography and dry etching. . When photolithography is employed, it is also a preferable aspect that a protective film such as SiO ₂ is formed on the entire surface by plasma CVD or the like prior to photolithography. The first electrode 8 is preferably formed into an ohmic electrode after annealing in a nitrogen atmosphere.

The step of forming the second electrode 9 is not limited, but can be formed by vacuum deposition. Although this step is not limited, for example, a protective film such as SiO ₂ is formed on the entire surface by a plasma CVD method or the like, and a current injection window is formed on the p-type contact layer 8 by patterning. Forming the two electrodes 9 is a preferred form. The second electrode 9 is also preferably an ohmic electrode by annealing in a nitrogen atmosphere, like the first electrode. The annealing and the protective film formation can be performed simultaneously with the first electrode 8 formation step.

  Through the above steps, the polycrystalline LED according to the present embodiment can be manufactured.

  As one of the embodiments, application to a solar cell is also possible. The structure of the solar cell is similar to that of the LED according to this embodiment, and the thickness of each layer is different, but the substrate 1, the low-temperature relaxation layer 2, the n-type contact layer 3, the n-type cladding layer 4, the polycrystalline active layer 5, and the p-type. The clad layer 6 and the p-type contact layer 7 are sequentially laminated. The first electrode 8 is formed on the n-type contact layer 2 and the second electrode 9 is formed on the p-type contact layer 7. Are stacked. The respective layers and electrodes in the present embodiment are substantially the same in function as those in the first embodiment, and the description thereof is omitted.

  In order to confirm the effect of the polycrystalline semiconductor device according to the above embodiment, GaN and InGaN polycrystalline structures were actually created and evaluated on a polycrystalline AlN substrate. This will be described below.

(Manufacturing method of GaN polycrystalline structure on polycrystalline AlN substrate)
A polycrystalline AlN substrate was used as the substrate. For the growth, a GaN polycrystal low temperature relaxation layer was grown using a metal organic vapor phase (MOCVD) growth method, and then the GaN polycrystal layer was grown to 2 to 7 μm.

(Effect of low-temperature relaxation layer on GaN polycrystalline growth on polycrystalline AlN substrate)
In the growth process, a polycrystalline AlN substrate is first heat-treated in an MOCVD apparatus for 30 minutes at 1100 ° C., then a GaN relaxation layer is formed at a low temperature of 550 ° C., and then the substrate temperature is raised to 1080 ° C. Grew up.
The surface coverage of the GaN polycrystalline layer varies depending on the presence or absence of the GaN low-temperature relaxation layer. FIG. 3 shows changes in surface morphology depending on the presence or absence of a low-temperature relaxation layer of polycrystalline GaN. Here, the growth pressure was constant at 200 Torr. As can be seen by comparing electron microscope images of the surface, it can be seen that when the GaN low-temperature relaxation layer is used, the surface coverage is improved. That is, it can be seen that the GaN low-temperature relaxation layer is effective in increasing the coverage of the polycrystalline GaN layer. The coverage of polycrystalline GaN grown using the low-temperature relaxation layer is 81%, but it is reduced to 66% when not used.

(Effect of growth pressure on GaN polycrystal growth on polycrystal AlN substrate 1)
Since the effect of the low-temperature relaxation layer was confirmed, the above-mentioned GaN low-temperature relaxation layer was inserted into all the growth processes, and this time the growth pressure was changed to grow a polycrystalline GaN layer. The growth temperature was fixed at 1080 ° C., and the growth pressure was changed to 30, 76, 200, and 300 Torr, and the growth was performed for 1 hour. FIG. 4 shows electron microscope images of the surface and the cross section. It can be seen that the coverage of the polycrystalline GaN on the surface approaches 100% as the growth pressure decreases.
Moreover, it can be seen from the cross-sectional electron microscope image that each crystal grain of polycrystalline GaN grows along the crystal grain of polycrystalline AlN which is the substrate, and the characteristics of each crystal grain itself are equivalent to the single crystal itself. it is conceivable that.
It can also be seen that when the growth pressure is lowered, the flatness of the surface is improved. This shows that the surface coverage and surface flatness can be controlled by appropriately selecting the growth pressure.

(Effect of growth pressure on GaN polycrystal growth on polycrystal AlN substrate 2)
FIG. 5 shows the result of X-ray diffraction measurement of a polycrystalline GaN sample grown by changing the growth pressure. For comparison, the result of a polycrystalline AlN substrate on which GaN is not grown is also shown. Diffraction peaks from a plurality of crystal orientations indicating the formation of a polycrystalline structure are observed. In the polycrystalline GaN sample, a peak clearly different from that of polycrystalline AlN is observed, and it can be confirmed that the GaN polycrystalline is growing. These diffraction peaks also change depending on the growth pressure. When the growth pressure is as low as 30 Torr, it can be seen that the diffraction peak on the (0002) plane is strong and the orientation of the polycrystalline film is improved.
That is, the surface coverage, flatness, and orientation are improved at a low growth pressure of 30 Torr.

(Effect of growth pressure on GaN polycrystal growth on polycrystal AlN substrate 3)
FIG. 6 shows a room temperature photoluminescence spectrum of a polycrystalline GaN sample grown at different growth pressures. Here, a photoluminescence measurement result of a commercially available single crystal bulk GaN substrate is also shown for comparison. The emission intensity from polycrystalline GaN is higher as the growth pressure is higher, and the emission peak intensity is reduced to about 1/10 at a pressure as low as 30 Torr compared to bulk GaN. However, even in the sample grown at 300 Torr, the emission intensity was equivalent to that of the bulk GaN sample, but the emission on the low energy side other than the forbidden band width (360 nm) of GaN was dominant.

(Growth Temperature Dependence in GaN Polycrystalline Growth on Polycrystalline AlN Substrate 1)
Next, the growth temperature dependence of polycrystalline GaN was examined. The growth pressure was 300 Torr, which showed relatively good optical characteristics, and the growth temperature of polycrystalline GaN was changed to 550, 700, 800, 900, 1080 ° C. FIG. 7 shows a surface electron microscope image of polycrystalline GaN. Although an uncoated region can be seen at a growth temperature of 1080 ° C., the coverage can be improved by lowering the growth temperature in the same manner as controlling the growth pressure, and a coverage of almost 100% can be achieved at 900 ° C. or less. did it. Further, the surface roughness (expressed by RMS value) was smaller as the growth temperature was lower, and the lowest value of 0.09 mm was obtained at 550 ° C. The above results indicate that the coverage and surface flatness can be controlled by appropriately selecting the growth temperature.

(Growth temperature dependence in GaN polycrystal growth on polycrystal AlN substrate 2)
FIG. 8 shows a room temperature photoluminescence spectrum of a polycrystalline GaN sample with the growth temperature changed. For comparison, the results of a single crystal bulk GaN sample are also shown. It was found that the sample with the growth temperature set at 900 ° C. showed substantially the same emission intensity and half width as single crystal bulk GaN. In other words, it was found that by optimizing the growth pressure and growth temperature, it is possible to improve the coverage, flatness, and optical characteristics of a polycrystalline structure having large crystal grains. Specifically, to realize a polycrystalline GaN structure with excellent optical properties, (1) introduction of a low-temperature GaN relaxation layer (2) high growth pressure (-300 Torr) (3) optimum growth temperature (-900 ° C) The selection of was found to be important.
The excellent optical characteristics of such a polycrystalline GaN sample are the result of positively using randomly oriented crystal grains having an area sufficiently larger than the minority carrier diffusion length (several tens of nm) in GaN. In other words, it was experimentally suggested that high-efficiency light emission can be obtained by random control of each polycrystalline and microcrystalline grains even in a polycrystalline structure that is inexpensive and easy to increase in area, and that it can be applied to optical devices sufficiently. .

(Example 2)
(Polycrystalline InGaN mixed crystal growth)
Next, in order to investigate the effect of random control of polycrystalline and microcrystalline grains, a polycrystalline InGaN mixed crystal is grown on the above-mentioned polycrystalline GaN, and the composition and optical characteristics of the InGaN mixed crystal grown on each crystalline grain. Examined.

  The polycrystalline InGaN mixed crystal was grown on the above-described polycrystalline GaN film at a growth temperature of 700 to 800 ° C. The growth pressure was constant at 200 Torr. InGaN mixed crystals with different compositions were prepared and evaluated by changing the growth temperature and the raw material supply ratio of indium and gallium.

FIG. 9 shows a surface / cross-sectional electron microscope image (about 70 μm × 100 μm) of polycrystalline InGaN. The standard deviation of the crystal grain area of the polycrystalline InGaN mixed crystal is about 130 mm ² , indicating that crystal grains sufficiently larger than the minority carrier diffusion length of the GaN single crystal are formed. It can also be seen from the cross-sectional image that an InGaN / GaN polycrystalline structure grows along each underlying crystal grain on the polycrystalline AlN substrate.

FIG. 10 shows a surface electron microscope image of the polycrystalline InGaN sample and its EBSP measurement result. From the comparison of the two images, it can be confirmed that each crystal grain forms a polycrystalline structure having different plane orientations, and it can be seen that each crystal grain has crystallinity close to that of a single crystal. In the EBSP of FIG. 9B, the crystal planes of the red, blue, and green crystal grains correspond to (0002), (1-120), and (10-10) facets.

  FIG. 11 shows a low temperature PL spectrum. In this figure, the results of single crystal InGaN grown under the same conditions as the measurement results of four polycrystalline InGaN samples are also shown. The In composition of single crystal InGaN grown under the same conditions was (i) 9%, (ii) 16%, (iii) 25%, and (iv) 40%. It can be seen that a broad emission spectrum is obtained compared to the photoluminescence spectrum of the InGaN single crystal indicated by the dotted line. It can also be seen that as the In composition increases, the emission wavelength becomes longer and light emission from the red region is also obtained.

FIG. 12 shows the results of cathodoluminescence measurement of the sample shown in FIG. 10 (In composition is (iii) 25%). The emission images when the wavelength of the spectroscope is fixed at 515 nm and 590 nm are shown respectively. Obviously, the images obtained at wavelengths of 515 nm and 590 nm are different, and it can be seen that each crystal grain has a different emission wavelength. That is, by controlling each facet, InGaN crystal grains having various In compositions can be grown, and a broad emission wavelength in the visible light region can be obtained. This result shows that a white light device can be realized by polycrystalline random facet control without using a phosphor.

  FIG. 13 shows the cathodoluminescence spectrum obtained from each crystal grain. Here, the result of polycrystalline InGaN having an In composition (iv) of 40% was used. The light emission from the (0002), (1-120), and (10-10) facets was different, and it was confirmed again that each crystal grain had a different In composition. It was also found that the In composition of each crystal grain was higher in the order of the crystal planes (10-10), (1-120), and (0002). These results indicate that the In composition can be controlled by controlling each crystal grain and facet, and the color rendering property of white light can also be controlled.

  FIG. 13 shows a photoluminescence spectrum of a polycrystalline InGaN sample on polycrystalline GaN and a polycrystalline InGaN / GaN double heterostructure having substantially the same structure as that of the embodiment shown in FIG. For comparison, a spectrum of a nitride semiconductor white LED using a normal phosphor and a fluorescent lamp is also shown. Already put into practical use, white LEDs and fluorescent lamps have a very broad emission spectrum in the visible light range, but blue (400-450 nm) is also present in the polycrystalline InGaN mixed crystal and its double heterostructure produced by this embodiment. ) To red (600 nm) has been obtained, suggesting the possibility of application to a novel white light device having a polycrystalline InGaN structure by random facet control.

  As described above, it was confirmed that the effects of the polycrystalline semiconductor optical functional device according to the above embodiment can be achieved by the above examples. As described above, a novel semiconductor optical device can be realized.

  The semiconductor optical device according to the present invention can be industrially used as an LED or a solar cell. Furthermore, it can be used in a wide range of fields such as light receiving elements and electronic devices.

Surface SEM, EBSP image and color map of polycrystalline AlN substrate 1 is a schematic cross-sectional view of a polycrystalline LED according to an embodiment. . Effect of low-temperature relaxation layer of polycrystalline GaN film: (a) No relaxation layer (b) With relaxation layer Growth pressure dependence of surface and cross-sectional SEM images of polycrystalline GaN films. The numerical value in a figure shows a coverage. Growth pressure dependence of XRD measurement results for polycrystalline GaN films. The bottom is the XRD measurement result of the polycrystalline AlN substrate. Growth pressure dependence of room temperature PL spectrum of polycrystalline GaN film. Growth temperature dependence of surface SEM image of polycrystalline GaN film. The numerical value indicates the surface roughness. Growth temperature dependence of room temperature PL spectrum of polycrystalline GaN film. The surface and cross-sectional SEM image of a polycrystal InGaN film | membrane. Surface SEM image and EBSP image of polycrystalline InGaN film. Low temperature PL spectrum of polycrystalline InGaN film. In the figure, the solid line is the measurement result of polycrystalline InGaN, and the dotted line is the measurement result of single crystal InGaN grown under the same conditions. The panchromatic image by CL of the SEM image shown in FIG. (a) Light emission image at a wavelength of 515 nm (b) 590 nm. Emission spectrum from each crystal orientation by CL measurement of polycrystalline InGaN sample

Claims (5)

A microcrystalline nitride semiconductor electronic device comprising a plurality of crystal grains having random crystal faces,
A microcrystalline nitride semiconductor electronic device in which InGaN mixed crystal microcrystals having different compositions or film thicknesses on different crystal planes are formed. ^2. The microcrystalline nitride semiconductor electronic device according to claim 1, wherein 90% or more of the plurality of crystal grains has the crystal plane having an area of 1 mm ² or more.   2. The microcrystalline nitride semiconductor electronic device according to claim 1, wherein an area of the plurality of crystal grains is sufficiently larger than a diffusion length of minority carriers in the crystal grains.   The microcrystalline nitride semiconductor electronic device according to claim 1, wherein diffraction from two or more different crystal plane orientations is observed when 2θ / θ scan of X-ray diffraction measurement is performed. The microcrystalline nitride semiconductor electronic device according to claim 1, wherein the presence of the crystal grains having two or more different crystal planes can be confirmed by a scanning electron microscope or a backscattered electron diffraction image.