CN110911274B - III-nitride epitaxial film and selective area growth method thereof - Google Patents
III-nitride epitaxial film and selective area growth method thereof Download PDFInfo
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Abstract
The invention discloses a III-group nitride epitaxial film and a selective area growth method thereof.A transferred carbon nano tube is used as a dislocation cut-off layer above a graph of a patterned substrate, a composite substrate with a space structure is prepared by utilizing a periodic carbon nano tube array, and the process of inducing dislocation bending by a micrometer graph and the process of realizing dislocation cut-off by a nano porous layer are completed through one-step growth, so that the dislocation is effectively reduced, and the high-quality III-group nitride epitaxial film is obtained. The method has the advantages of simple process, low cost and high compatibility, and is very convenient for industrial application.
Description
Technical Field
The invention belongs to the technical field of semiconductor photoelectron, relates to a preparation technology of a III-group nitride epitaxial film, and particularly relates to a high-quality III-group nitride epitaxial film with a carbon nano tube as a dislocation cut-off layer on a patterned substrate and a selective area growth method thereof.
Background
Group III nitrides have great advantages of no alternatives in the field of short wavelength photoelectrons, but due to the difficulty and high price of single crystal preparation of group III nitride objects, commercially available group III nitride thin films are mainly obtained by epitaxy on a foreign substrate.
Among the commonly used heterogeneous substrates, sapphire substrates are currently the most widely used substrate in laboratory research and industrial production due to their ease of mass production and low cost. However, the sapphire substrate and the group III nitride have larger lattice mismatch and thermal mismatch, resulting in higher dislocation density and significantly influencing the photoelectric properties of the device, especially for the next generation of ultraviolet light emitting devices. Two major main epitaxial techniques, patterned substrate and lateral epitaxy, formed in the past in the industrialization process of blue light emitting devices can only reduce the dislocation density to-10 8 /cm 2 Multiple lateral epitaxy, stacked masking, etc., although the dislocation density can be reducedReduce to 10 of commercial requirement 7 /cm 2 However, these techniques often require multiple processes and even multiple epitaxial growths, and are complicated in process and high in cost, and thus are still difficult to be applied industrially. The high dislocation density brings the efficiency bottleneck problem and the heat dissipation problem of the ultraviolet light-emitting device, the junction temperature of the device is increased, the light-emitting intensity and the service life are deteriorated, the heat conductivity of the sapphire substrate is relatively small, the heat dissipation capability is relatively weak, and the heat dissipation problem of the device is particularly obvious. Reducing the dislocation density in epitaxial structures and thus improving device heat dissipation in a simple and efficient manner, while taking into account the cost of technology implementation, has become a focus of recent attention in the field of short wavelength photonics.
The carbon nanotube is a tubular carbon molecule, the radial dimension of which is in the nanometer level, the axial dimension of which is in the micrometer level, and the carbon nanotube has a huge length-diameter ratio and is a typical one-dimensional material. The carbon atom on the surface of the material is sp 2 The hybrid C-C bond is connected, the outer wall is smooth, no dangling bond exists, the high temperature and the conventional acid and alkali are resisted, and the physical and chemical properties are stable. The above-mentioned morphology and physical properties determine that reactants and intermediates in vapor phase epitaxy are generally difficult to attach to carbon nanotubes. In addition, the research shows that the axial thermal conductivity of the carbon nano tube is 3000-6600W/mK, and the carbon nano tube has good thermal conductivity. As a new carbon material discovered earlier, carbon nanotubes have been produced in large quantities, at low cost, and are capable of orientation and transfer. The preparation process only involves few raw materials, the reaction is relatively sufficient, the concentration of residual impurities is extremely low, and the requirements of the semiconductor industry are met.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides the III-nitride epitaxial film and the selective area growth method thereof.
The core of the invention is: in order to solve a series of problems of low light efficiency and high heat production caused by high dislocation density in a short wavelength light-emitting device, difficulty in heat dissipation caused by a sapphire substrate and the like, the invention provides a selective growth method and a selective growth structure of a high-quality III-group nitride epitaxial film by taking transferred carbon nanotubes as dislocation cut-off layers above a pattern of a patterned substrate. The composite substrate with a special space structure is prepared by means of a periodic carbon nanotube array, two independent processes of 'micron pattern induced dislocation bending' and 'dislocation cutoff realized by a nano porous layer' can be combined through one-time growth, so that a high-quality III-group nitride epitaxial film can be obtained, the process is simple, the cost is low, the peak internal quantum efficiency (representing the efficiency of converting electric energy into light energy) of the prepared device is greatly improved, the light output power (under the same working current), the saturation current and the saturation light power are also greatly improved, and the heat generation of the device is reduced by the high photoelectric conversion efficiency. Furthermore, the strong heat dissipation capability of the carbon nano tube makes up the deficiency of the sapphire substrate in heat dissipation. The junction temperature of the device can be obviously reduced by improving heat dissipation on the basis of reducing heat generation, and the reduction of the junction temperature is also beneficial to the improvement of the electro-optic conversion efficiency. The invention combines the crystal quality improvement and the heat radiation improvement into a whole, realizes two mutually-promoted functions by one process, and has the advantages of simple structure, convenient implementation and cost advantage compared with the prior complex designs which utilize new materials such as carbon-based materials and the like to simply improve the crystal quality (or simply improve the heat radiation effect).
The technical scheme provided by the invention is as follows:
a selectively grown high quality group III-nitride epitaxial film, comprising: patterning the substrate; the carbon nano tube dislocation cut-off layer is paved above the graphical substrate graph and consists of a single-layer or multi-layer carbon nano tube film, and each layer of carbon nano tube film is a carbon nano tube array which is arranged in parallel; and growing and finally folding the III-nitride epitaxial film in the window of the carbon nano tube dislocation stop layer.
The patterned substrate can be a patterned substrate with protrusions, recesses or other special-shaped structures such as a bag-shaped substrate, a cone-shaped substrate, a hole-shaped substrate and the like, and can comprise a substrate with a periodic micrometer-scale structure formed by one or more patterns in the same or different distribution.
When the dislocation cut-off layer is prepared, firstly, a carbon nano tube film is generated: on the growth substrate of the carbon nano tube array, a layer of regularly arranged and uniform nano-scale iron powder is evaporated and deposited by an electron beam to be used as a catalyst, then the array consisting of the carbon nano tubes arranged in parallel is grown by using acetylene as a carbon source under low pressure and high temperature through a low-pressure chemical vapor deposition method, and then the array is used as a layer of carbon nano tube film to be transferred to the graph of the patterned substrate. The carbon nano tube dislocation cut-off layer is composed of single-layer or multi-layer carbon nano tube films, and the diameter of the carbon nano tube in each layer of film can be single-wall or multi-wall, and the diameter of a single carbon nano tube is between 10 and 100nm.
The invention selects different carbon nano tube dislocation cut-off layers according to different graphs and different III-nitride growth modes aiming at different patterned substrates. The carbon nanotube dislocation cut-off layer can comprise a single-layer or multi-layer carbon nanotube film, so the size and the structure of a window in the cut-off layer can be flexibly and accurately controlled by controlling the number of layers of the laid carbon nanotube film according to actual needs: the more the number of layers is laid, the smaller the size of the window in the cut-off layer is; the single-layer carbon nanotube film is a carbon nanotube array arranged in parallel, and the multiple layers of carbon nanotube films can be arranged in parallel, vertically or across at an acute angle according to requirements, so that the multiple layers of carbon nanotube films can be used for constructing a cut-off layer with any window shape such as rectangle, hexagon, parallelogram and the like.
In the invention, the carbon nano tube is positioned above the patterned substrate pattern. This spatial structure means that in the initial stage of epitaxial growth of group III nitride, the micron-scale pattern on the patterned substrate surface will first serve as a one-time selective growth: because the growth conditions of the III-nitride on different crystal planes of the patterned substrate are obviously different, for example, the growth conditions of the III-nitride on a c plane and a non-c plane cannot be met at the same time, the nucleation islands can be mainly distributed between the patterns of the patterned substrate in actual growth, more sufficient lateral epitaxy can occur in the growth process of the nucleation islands, the mirror image force of the free surface can promote the threading dislocation in the III-nitride to incline, partial dislocation with larger inclination degree is stopped on the surface of the III-nitride contacted with the patterns, the threading dislocation is not extended, and the dislocation density is reduced. The fact that the carbon nano tube dislocation stop layer is located above the patterned substrate pattern means that when a group III nitride island growing along with lateral epitaxy is close to the top end of the pattern, partial dislocations which are slightly inclined or even basically not inclined due to the mirror force are stopped by the carbon nano tube dislocation stop layer with high duty ratio at a high probability, and the group III nitride growing from a large number of nano-scale windows in the dislocation stop layer has high crystal quality. The carbon nanotube layer also improves the heat diffusion capability along the surface of the III-nitride film, increases the available interface area of the heat diffusion along the longitudinal direction of the device, and enables more channels for heat to be radiated out of the device.
The invention also provides a method for selective growth of high-quality group III nitride epitaxial films, which comprises the following steps: the transferred carbon nano tubes are used as dislocation cut-off layers above the patterns of the patterned substrate, the composite substrate with a special space structure is prepared by utilizing the carbon nano tube array with periodicity, the dislocation cut-off process is realized by completing the process of inducing dislocation bending by a micron pattern and a nano porous layer through one-time growth, the dislocation is effectively reduced, and the high-quality III-group nitride epitaxial film is obtained; the method comprises the following steps:
1) Selecting a patterned substrate:
the patterned substrate with protrusions, recesses or other special-shaped structures such as bag-shaped, cone-shaped and hole-shaped structures can be selected, or the substrate with periodic micrometer-scale structures formed by one or more patterns in the same or different distribution can be selected.
2) Using the transferred carbon nanotubes as dislocation cut-off layers above the pattern of the patterned substrate: growing a carbon nanotube film, and laying a single-layer or multi-layer carbon nanotube film on the patterned substrate to form a carbon nanotube dislocation stop layer;
the grown carbon nanotube film is stripped from a substrate on which the carbon nanotube film grows, then a single-layer or multi-layer carbon nanotube film is laid on the patterned substrate according to the requirement to form the carbon nanotube dislocation stop layer, each layer of carbon nanotubes is a carbon nanotube array which is arranged in parallel, and the multi-layer carbon nanotube film can be arranged into various shapes, such as being arranged in parallel, vertically or crossed into an acute angle, so that the multi-layer carbon nanotube film is used for constructing the carbon nanotube dislocation stop layer with any window shape, such as rectangle, hexagon, parallelogram and the like.
When the dislocation cut-off layer is prepared, firstly, a layer of regularly arranged and uniform-sized nanoscale iron powder is evaporated and deposited on a growth substrate of a carbon nano tube array through an electron beam to serve as a catalyst, then, an array consisting of carbon nano tubes arranged in parallel is grown through a low-pressure chemical vapor deposition method by taking acetylene as a carbon source at low pressure and high temperature, and then, the array is taken as a layer of carbon nano tube film to be transferred to a pattern of a patterned substrate. The carbon nano tube dislocation cut-off layer is composed of single-layer or multi-layer carbon nano tube films, and the diameter of the carbon nano tube in each layer of film can be single-wall or multi-wall, and the diameter of a single carbon nano tube is between 10 and 100nm.
3) Growing a III-nitride epitaxial film on the patterned substrate paved with the carbon nano tube dislocation stop layer:
the group III nitride epitaxial film may be grown by Metal Organic Chemical Vapor Deposition (MOCVD), molecular Beam Epitaxy (MBE), hydride Vapor Phase Epitaxy (HVPE), or the like. When growing a group III nitride epitaxial film at a high temperature by MOCVD, hydrogen, nitrogen or a mixed gas of the two is used as a carrier gas, a group III metal organic compound is used as a group III source, the flow rate of the carrier gas is 10-500 sccm, ammonia gas is used as a group V source, the flow rate of the carrier gas is 10-10000 sccm, the molar flow rate ratio of the group III source to the group V source (V/III, which is the ratio of the number of particles of the group III source to the number of particles of the group V source fed into a reaction chamber in unit time) is 50-8000, the temperature is 800-1100 ℃, and the pressure is 50-500 Torr. By changing the growth time, high-quality III-nitride epitaxial thin films with the thickness between 10nm and 10 mu m can be grown.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a high-quality III-nitride epitaxial film taking a carbon nano tube as a dislocation cut-off layer on a patterned substrate and a selective area growth method thereof, which have the following technical advantages that:
(1) The invention leads the dislocation bending induced by the micron pattern and the dislocation bending induced by the nano porous layer to be directly cut off two independent processes for effectively reducing the dislocation; reducing the dislocation density of a group III nitride epitaxial film to-10 with simpler process and at lower cost 7 /cm 2 The problems that the traditional schemes such as multiple lateral epitaxy, laminated mask and the like can only annihilate partial dislocation with small inclination degree through the interaction between dislocations and have low efficiency are solved; can meet the requirements of various commercial III-nitride photoelectric devices on the crystal quality.
(2) Compared with the traditional III-nitride device heat management technology of wafer bonding, inversion and addition of a metal or carbon-based heat dissipation layer, the invention combines a dislocation control structure and an optional heat dissipation structure into a whole, achieves two mutually-promoted effects of high-quality and high-efficiency heat production reduction and rapid heat dissipation and junction temperature reduction and efficiency improvement by one process, and realizes simpler and more effective heat management.
(3) The invention is suitable for various commercial patterned substrates, the adopted carbon nano tube can be prepared massively and has low price, and the whole process does not need other special materials or special procedures, thereby being well compatible with the existing production line equipment and process flow and being very convenient for industrialized application.
Drawings
FIG. 1 is an embodiment of selective growth of high quality group III-nitride epitaxial films according to the present invention: a schematic diagram of a round-bag type patterned substrate and a composite substrate which is arranged above the round-bag pattern and takes two carbon nano tube layers with the inner parts parallel to each other and mutually orthogonal to each other as dislocation cut-off layers;
FIG. 2 is a schematic view of two independent processes for effectively reducing dislocations, combining "micro pattern induced dislocation bending" and "nanoporous layer implemented dislocation cutting" in the method for selective growth of high quality group III nitride epitaxial films of the present invention;
FIG. 3 is a graph of the raw results of measuring dislocation density of a group III nitride epitaxial film according to a widely used cathode fluorescence method in a method for selective growth of a high quality group III nitride epitaxial film according to the present invention;
FIG. 4 is a schematic diagram of a carbon nanotube layer rapidly and relatively uniformly spreading heat collected at a position of an n-electrode of an n-type layer adjacent to a subsequent epitaxy in a group III nitride thin film to the entire carbon nanotube layer in a high quality group III nitride epitaxial thin film of the present invention;
fig. 5 is a measurement result of optical power and junction temperature of a light emitting diode fabricated based on the high-quality group III nitride epitaxial thin film of the present invention;
FIG. 6 is an embodiment of the selective growth of high quality group III-nitride epitaxial films of the present invention: a schematic diagram of a triangular pyramid patterned substrate and a composite substrate above the triangular pyramid pattern, wherein three carbon nanotube layers which are parallel to each other in the interior and have an included angle of 60 degrees with each other are used as dislocation cut-off layers;
FIG. 7 is an embodiment of the selective growth of high quality group III-nitride epitaxial films of the present invention: a schematic diagram of a composite substrate formed by combining a sapphire substrate, an aluminum nitride layer with a strip-shaped pattern on the sapphire substrate and a layer of carbon nanotubes which are parallel to each other and vertical to the strip direction and are positioned above the strip-shaped pattern;
in fig. 1 to 2, 4, 6 to 7, 1 is a substrate; 2 is a graph; 3 is a gap between the patterns; 41. 42, 43 are the first, second, third carbon nanotube film above the figure respectively, make up the dislocation and stop the layer; 5 is a window in the carbon nanotube dislocation stop layer;
in fig. 2, 6 is a nucleation island in the inter-pattern space; 7 is a threading dislocation; 8 is carbon nanotube and hole wrapping carbon nanotube;
in fig. 2, 4, 9 is a high-quality group III nitride epitaxial film; 10 is an n-type group III nitride epitaxial layer on the group III nitride epitaxial film; 11 is an n-electrode on the n-type group III nitride epitaxial layer; 12 is the current in the light emitting process of the device; the heat flow generated by the current is 13.
Detailed Description
The present invention provides a high quality group III nitride epitaxial thin film on a patterned substrate using carbon nanotubes as dislocation cutoff layers and a selective growth method thereof, which will be further described by way of example with reference to the accompanying drawings, without limiting the scope of the invention in any way.
Example one
In this embodiment, the composite substrate includes a round-bag type patterned substrate and a dislocation-cutting layer having two carbon nanotube layers inside parallel to each other and orthogonal to each other above the round-bag pattern.
The high quality III-nitride epitaxial film and the selective growth method thereof of the present embodiment include the following:
1) Preparing a composite substrate:
a) A layer of regularly arranged nanoscale iron powder with uniform size is deposited on a growth substrate of a carbon nano tube array through electron beam evaporation to serve as a catalyst, and then an array consisting of carbon nano tubes arranged in parallel is grown by using acetylene as a carbon source at low pressure and high temperature through a low-pressure chemical vapor deposition method, wherein the carbon nano tubes are multi-wall carbon nano tubes, and the diameter of a single carbon nano tube is about 50 nm.
b) And stripping the grown carbon nanotube film from the substrate on which the carbon nanotube film is grown. As shown in FIG. 1, a layer of carbon nanotubes 41 with their inner portions parallel to each other is laid on top of a pattern 2 (height 1.5 μm, diameter 3 μm, pattern pitch 0.5 μm) of a round-covered patterned substrate 1, with the direction parallel to the reference edge of the substrate.
c) Similarly, a second layer of carbon nanotubes 42 is laid over the first layer of carbon nanotubes, with the inner carbon nanotubes parallel to each other and oriented perpendicular to the reference edge of the substrate.
2) Growing a high-quality gallium nitride epitaxial film based on the composite substrate to form a high-quality group III nitride epitaxial thin film 9 in fig. 2:
a) Hydrogen and nitrogen were used as carrier gases, the flow rate of gallium source was 25sccm, the flow rate of ammonia gas was 5000sccm, V/III was 4200, the temperature was 1030 ℃, and the pressure was 300Torr. The growth time was controlled to grow a high-quality group III nitride epitaxial thin film 9 with a thickness of 1 μm.
b) After growingIn the process, as shown in fig. 2, gallium nitride first forms nucleation islands 6 between the gaps 3 of the substrate pattern, the islands containing a high density of threading dislocations 7. In the subsequent growing and folding process of the nucleation island, lateral epitaxy occurs, the oblique side surface generates mirror image force to induce the direction of partial threading dislocation to obviously deflect, and as the nucleation island grows continuously, the dislocation obviously deflected in the direction is finally stopped on the surface of the III group nitride in contact with the graph 2 and does not extend any more. The dislocation without obvious deflection direction, most of which is cut off by the carbon nano tube 41,42 with high duty ratio (essentially by the formed holes wrapping the carbon nano tube) when the nucleation island approaches the top end of the pattern 2, only a small part of threading dislocation can pass through the window area 5 in the dislocation cut-off layer formed by the carbon nano tube and continue to extend upwards, and the high-quality III-group nitride epitaxial film 9 with the thickness of 2.5 mu m and the dislocation density of 3.5 multiplied by 10 is obtained through the processes 7 /cm 2 (measurement according to the widely used cathodoluminescence method, the raw results of the measurement are shown in FIG. 3).
Example two
In this example, the high-quality group III nitride epitaxial thin film 9 demonstrated in example one was used as a template to continue epitaxial production of the short-wavelength light-emitting device shown in fig. 4
1) An n-type group III nitride epitaxial layer 10 is epitaxially grown on the epitaxial thin film 9 as shown in fig. 4. Hydrogen and nitrogen are used as carrier gas, the flow rate of a gallium source is 25sccm, ammonia is used as a group V source, the flow rate is 5000sccm, the V/III is 4200, the temperature of MOCVD growth is 1020 ℃, the pressure is 300Torr, the thickness of an n-type GaN layer is 1.5 mu m, an n-type carrier adopts silicon element for doping, the electron concentration is 10 18 /cm 3 .
2) The n-type group III nitride epitaxial layer is epitaxially provided with 15 periods of quantum wells. Each quantum well structure consists of a well region and a barrier region, wherein the well region is made of GaN material, hydrogen and nitrogen are used as carrier gas, the flow rate of a gallium source is 25sccm, ammonia is used as a V-group source, the flow rate is 5000sccm, the V/III is 4200, the temperature of MOCVD growth is 1010 ℃, the pressure is 300Torr, and the thickness of the well region is 5nm; the barrier region is made of AlGaN material, hydrogen and nitrogen are used as carrier gas, the flow rate of a gallium source is 25sccm, the flow rate of an aluminum source is 45sccm, ammonia is used as a V-group source, the flow rate is 5000sccm, the V/III is 3500, the temperature of MOCVD growth is 1010 ℃, the pressure is 300Torr, and the thickness of the barrier region is 100nm.
3) Then, extending p-type GaN material, using hydrogen and nitrogen as carrier gas, gallium source flow rate of 25sccm, ammonia gas as group V source, its flow rate of 5000sccm, V/III of 4200, MOCVD growth temperature of 1000 deg.C, pressure of 100Torr, p-type region thickness of 500nm, doping Mg element, and hole concentration of 10 18 /cm 3 .
4) Finally, electrodes (11 are n electrodes) are respectively prepared on the p-type GaN and the exposed n-type GaN by utilizing conventional LED preparation technologies such as photoetching, electron beam evaporation, alloy and the like, the metal materials of the electrodes are Ti/Al/Ni/Au, the thickness is 200nm, chips with the size of 300 microns multiplied by 300 microns are prepared by laser scribing, and then packaging is carried out.
5) Thanks to the improvement in crystal quality, the output power at 300mA is improved by about 36.6% (as shown in fig. 5), and further in-depth analysis shows that the increase rate of the quantum efficiency in the peak reaches 58.2%, the saturation current is improved by 38%, and the saturation optical power is improved by 89%, during the light emission of the device, the current 12 is mainly concentrated near the n-electrode 11, and most of the joule heat 13 is also generated there, and then is transferred from there to the outside of the device through the high-quality III-nitride epitaxial thin film 9 and the substrate 1. Due to the existence of the dislocation cut-off layer 4 formed by the carbon nanotube layer, compared with the case without the dislocation cut-off layer, most of the joule heat 13 can be rapidly and relatively uniformly spread to the whole carbon nanotube layer 4, so that the available interface area for heat diffusion along the longitudinal direction of the device is increased, more channels for heat are provided for being emitted out of the device through the longitudinal path of the n-electrode 11, the n-type layer 10, the group III nitride film 9, the carbon nanotube layer 4 and the substrate 1, and the measured junction temperature of the device is averagely reduced by 10 ℃ (as shown in fig. 5).
Part of measured data is shown in the figure
EXAMPLE III
The triangular pyramid type patterned substrate is more advantageous in improving the light extraction efficiency of the photoelectric device than a round-clad patterned substrate, but is inferior to the latter in reducing the dislocation density, and the composite substrate prepared by combining the triangular pyramid type patterned substrate with the carbon nanotube dislocation cut-off layer can overcome the defects in the aspect.
The selective growth method of a high-quality group III nitride epitaxial film of the present embodiment includes the steps of:
1) Preparing a composite substrate:
a) On the growth substrate of the carbon nano tube array, a layer of regularly arranged and uniform-sized nanoscale iron powder is evaporated and deposited by an electron beam to be used as a catalyst, and then the array consisting of carbon nano tubes arranged in parallel is grown by using acetylene as a carbon source at low pressure and high temperature by a low-pressure chemical vapor deposition method, wherein the carbon nano tubes are single-wall carbon nano tubes, and the diameter of each single carbon nano tube is about 10 nm.
b) The grown carbon nanotube film is peeled off from the substrate on which it was grown, and as shown in FIG. 6, a layer of carbon nanotubes 41 whose insides are parallel to each other is laid on top of a pattern 2 (height 1.5 μm, bottom side length 2.6 μm, pattern pitch 0.5 μm) of a triangular pyramid type patterned substrate 1, with the direction parallel to the reference side of the substrate.
c) Similarly, a second layer of carbon nanotubes 42 is laid over the first layer of carbon nanotubes, with the inner carbon nanotubes parallel to each other and oriented at an angle of 60 degrees clockwise from the reference edge of the substrate.
d) Similarly, a third layer of carbon nanotubes 43 is laid over the second layer of carbon nanotubes, with the inner carbon nanotubes parallel to each other and oriented at 120 degrees clockwise from the reference edge of the substrate.
2) Growing a high-quality gallium nitride epitaxial film based on the composite substrate to form a high-quality III-group nitride epitaxial film:
a) Hydrogen and nitrogen are used as carrier gases, the flow rate of a gallium source is 28sccm, ammonia is used as a group V source, the flow rate is 5500sccm, the V/III is 4100, the temperature is 1030 ℃, and the pressure is 300Torr. The growth time is controlled, and a high-quality III-nitride epitaxial film with the thickness of 1 mu m is grown.
b) The threading dislocation was reduced during the growth in a manner similar to that of the example.
3) Subsequently, a device can also be prepared similarly to example two.
Example four
In this embodiment, the composite substrate includes a silicon substrate, an aluminum nitride layer on the silicon substrate, in which a long stripe pattern is etched, and a dislocation cut-off layer having a carbon nanotube layer inside parallel to each other over the long stripe. The silicon substrate with aluminum nitride deposited in advance is hopeful to serve as a substrate of III-nitride in the epitaxial preparation of electronic devices, but the control of epitaxial dislocation of the III-nitride on the substrate is more difficult, and the defect of the composite substrate prepared by combining the substrate with the carbon nanotube dislocation stop layer can be overcome.
The selective growth method of a high-quality group III nitride epitaxial film of the present embodiment includes the steps of:
1) Preparing a composite substrate:
a) On a growth substrate of a carbon nano tube array, a layer of regularly arranged nanoscale iron powder with uniform size is evaporated and deposited by an electron beam to be used as a catalyst, and then an array consisting of carbon nano tubes arranged in parallel is grown by using acetylene as a carbon source at low pressure and high temperature by a low-pressure chemical vapor deposition method, wherein the carbon nano tubes are multi-wall carbon nano tubes, and the diameter of a single carbon nano tube is about 100nm. Stripping the grown carbon nanotube film from the substrate
b) Cleaning a commercial silicon substrate 1 with hydrofluoric acid and deionized water, sending the silicon substrate into an MOCVD reaction chamber to grow a layer of aluminum nitride (or depositing the aluminum nitride by other common film coating means such as magnetron sputtering) so as to protect the silicon substrate from being damaged by a III-group or V-group source in subsequent growth, wherein hydrogen and nitrogen are used as carrier gases during MOCVD growth, the flow rate of an aluminum source is 45sccm, ammonia is used as a V-group source, the flow rate is 1000sccm, the V/III is 2900, the temperature of MOCVD growth is 1090 ℃, the pressure is 200Torr, after the growth is finished and the temperature is reduced, a long strip-shaped pattern 2 (the height is 1.5 mu m, the bottom surface side length is 2.5 mu m, and the pattern interval is 5 mu m) is prepared by adopting a traditional planar process through etching, as shown in figure 7, a layer of carbon nanotubes 41 with the inner parts parallel to each other is laid above the pattern, and the direction is vertical to the extending direction of the long strip.
2) Growing a high-quality gallium nitride epitaxial film based on the composite substrate to form a high-quality III-group nitride epitaxial film:
a) Hydrogen and nitrogen were used as carrier gases, the flow rate of gallium source was 25sccm, the flow rate of ammonia gas was 5000sccm, V/III was 4200, the temperature was 1030 ℃, and the pressure was 300Torr. The growth time is controlled, and a high-quality III-nitride epitaxial film with the thickness of 1 mu m is grown.
b) The threading dislocation was reduced during the growth in a manner similar to that of the example.
3) Subsequently, a device can also be prepared similarly to example two.
Finally, it is noted that the disclosed embodiments are intended to aid in further understanding of the invention, but those skilled in the art will appreciate that: various substitutions and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the invention should not be limited to the embodiments disclosed, but the scope of the invention is defined by the appended claims.
Claims (9)
1. A selective area growth method of a high-quality III-group nitride epitaxial film is characterized in that transferred carbon nanotubes are used as dislocation cut-off layers at the top end of a graph of a patterned substrate, a composite substrate with a space structure is prepared by utilizing a periodic carbon nanotube array, a process of inducing dislocation bending by a micrometer graph and a process of realizing dislocation cut-off by a nano porous layer are completed through one-time growth, dislocation is effectively reduced, and the high-quality III-group nitride epitaxial film is obtained; the method comprises the following steps:
1) Selecting a patterned substrate, wherein the patterned substrate is a substrate with a periodic micrometer scale structure; selecting a bag-shaped, conical or hole-shaped patterned substrate; the patterned substrate is provided with a special-shaped structure comprising protrusions and depressions;
2) Growing a carbon nano tube film;
the growing carbon nanotube film specifically comprises the following steps: depositing a layer of regularly arranged nanoscale iron powder with uniform size as a catalyst on a growth substrate of a carbon nanotube array by electron beam evaporation; then, by a low-pressure chemical vapor deposition method, acetylene is used as a carbon source at low pressure and high temperature to grow an array consisting of carbon nano tubes arranged in parallel as a layer of carbon nano tube film;
laying a single-layer or multi-layer carbon nanotube film on the top end of the patterned substrate to form a carbon nanotube dislocation cut-off layer;
controlling the size and structure of a window in the cut-off layer through the number of layers of the carbon nanotube film contained in the carbon nanotube dislocation cut-off layer;
3) And growing a high-quality III-group nitride epitaxial film with the thickness of 10 nm-10 mu m on the patterned substrate paved with the carbon nano tube dislocation cut-off layer.
2. The selective area growth method of a high quality group III nitride epitaxial film according to claim 1, wherein step 2) is to lay a single-layered or multi-layered carbon nanotube film on the patterned substrate, each layer of carbon nanotubes being an array of parallel arranged carbon nanotubes.
3. The method for selective area growth of high quality group III nitride epitaxial films according to claim 1 wherein in step 2) different carbon nanotube dislocation stop layers are selected for different patterned substrates depending on the pattern and the group III nitride growth mode.
4. The method for selective growth of high quality group III nitride epitaxial films according to claim 1 wherein in step 2) the plurality of carbon nanotube films are arranged parallel, perpendicular or crossing to each other at an acute angle; the shape of the array includes a rectangle, a hexagon or a parallelogram.
5. The method for selective growth of high quality group III nitride epitaxial films according to claim 1 wherein step 3) uses metalorganic chemical vapor deposition MOCVD, molecular beam epitaxy MBE, or hydride vapor phase epitaxy HVPE methods to grow group III nitride epitaxial films.
6. The selective growth method of a high-quality group III nitride epitaxial film according to claim 5, characterized in that, when the group III nitride epitaxial film is grown at a high temperature by the MOCVD method, hydrogen, nitrogen or a mixed gas of the two is used as a carrier gas; using III metal organic as III source with flow rate of 10-500 sccm; ammonia gas is used as a group V source, and the flow rate is 10-10000 sccm; V/III is between 50 and 8000, the temperature is between 800 and 1100 ℃, and the pressure is between 50 and 500 Torr.
7. A high quality group III nitride epitaxial thin film selectively grown by the method of any one of claims 1 to 6, comprising:
patterning the substrate;
the carbon nano tube dislocation cut-off layer laid at the top end of the graphical substrate is composed of single-layer or multi-layer carbon nano tube films, and each layer of carbon nano tube film is a carbon nano tube array arranged in parallel;
and growing and finally folding the III-nitride epitaxial film in the window of the carbon nano tube dislocation stop layer.
8. The selectively grown high quality epitaxial film of group III nitride of claim 7 wherein said patterned substrate is of the wrap-around, taper or hole type; or/and the patterned substrate can have a special-shaped structure comprising a protrusion and a recess; the patterned substrate comprises a substrate with a periodic micrometer-scale structure formed by one or more patterns in the same or different distribution.
9. The selectively grown high quality group III nitride epitaxial film of claim 7, wherein the carbon nanotubes in each carbon nanotube film layer can be single walled or multi-walled; the diameter of a single carbon nano tube is 10-100 nm; and/or, the multi-layer carbon nanotube film is arranged to be parallel, vertical or crossed to form an acute angle; the shape of the array includes a rectangle, a hexagon or a parallelogram.
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