Patterned Si substrate-based LED epitaxial wafer and preparation method therefor

Abstract

An patterned Si substrate-based LED epitaxial wafer and a preparation method therefor, the LED epitaxial wafer comprising: a patterned Si substrate (1) and an Al.sub.2O.sub.3 coating (2) growing on the patterned Si substrate (1); sequentially growing on the Al.sub.2O.sub.3 coating (2) are a nucleating layer (3), a first buffer layer (4), a first insertion layer (5), a second buffer layer (6), a second insertion layer (7), an n-GaN layer (8), a quantum well layer (9), a p-GaN layer (10), an n-electrode (14) electrically connected to the n-GaN layer and a p-electrode (13) electrically connected to the p-GaN layer. The present invention is suitable for the preparation of large-sized LED epitaxial wafers. Furthermore, the crystal quality is improved, and the light extraction efficiency of the LED die is improved.

Claims

1. A preparation method for a patterned Si substrate-based LED epitaxial wafer, characterized in that the preparation method comprising the steps of: S1, etching a Si substrate to form a patterned Si substrate with a patterned structure thereon; S2, growing an Al.sub.2O.sub.3 coating on the patterned Si substrate; and S3, growing an epitaxial layer on the Al.sub.2O.sub.3 coating, wherein the epitaxial layer further comprises a GaN or AlGaN nucleation layer, a stress buffer layer and a light emitting structure layer, wherein the stress buffer layer is disposed between the GaN or AlGaN nucleation layer and the light emitting structure layer, the stress buffer layer composed of insertion layers and buffer layers alternately, the epitaxial layer further comprising a first buffer layer, wherein the first buffer layer and the light emitting structure layer are configured to be sequentially grown on the GaN or AlGaN nucleation layer, and the preparation method further comprising the step of: etching off the patterned Si substrate by wet etching by using the Al.sub.2O.sub.3 coating as a barrier layer, and exposing a patterned Al.sub.2O.sub.3 coating.

2. The preparation method according to claim 1, characterized in that the GaN or AlGaN nucleation layer configured to be grown on the Al.sub.2O.sub.3 coating.

3. The preparation method according to claim 1, characterized in that the step S2 comprising: plating an Al layer on the patterned Si substrate, and then introducing oxygen ions to form the Al.sub.2O.sub.3 coating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description for the embodiments or the prior art will be briefly described below. Obviously, the drawings in the following description are only for some of the embodiments described in the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative work.

(2) FIG. 1FIG. 11 are process flow diagrams of a method for preparing an LED device with a patterned Si substrate according to an embodiment of the present invention, wherein:

(3) FIG. 1 is a schematic view of a Si (111) substrate;

(4) FIG. 2A to 2G are schematic views showing the formation of a patterned Si substrate on the Si (111) substrate;

(5) FIG. 3 is a schematic view showing a step of growing an Al.sub.2O.sub.3 coating on the patterned Si substrate;

(6) FIG. 4A and FIG. 4B are schematic views of epitaxial growth of a nucleation layer on the Al.sub.2O.sub.3 coating;

(7) FIG. 5A and FIG. 5B are schematic views showing epitaxial growth of a first buffer layer on the nucleation layer;

(8) FIG. 6 is a schematic view showing epitaxial growth of a stress buffer layer on the first buffer layer;

(9) FIG. 7 is a schematic view showing epitaxial growth of a light emitting structure on the stress buffer layer;

(10) FIG. 8 is a schematic view showing deposition of a metal layer with a soldering surface on the light emitting structure;

(11) FIG. 9 is a schematic view of transferring an LED epitaxial wafer onto a Si (100) substrate by soldering a mirror metal layer;

(12) FIG. 10 is a schematic view showing an ohmic contact p-electrode fabricated on the Si (100) substrate and an ohmic contact n-electrode fabricated on an n-GaN layer; and

(13) FIG. 11 is a schematic illustration of the removal of the patterned Si substrate.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(14) The invention will be described in detail below in conjunction with the specific embodiments shown in the drawings. However, the embodiments are not intended to limit the invention, and the structures, methods, or functional changes made by those skilled in the art in accordance with the embodiments are included in the scope of the present invention.

(15) Referring to FIG. 1 to FIG. 11, the method for preparing a patterned Si substrate-based LED epitaxial wafer in the embodiment specifically includes the following steps:

(16) (1) Preparing a flat Si substrate (as shown in FIG. 1), first etching a patterned structure on a flat Si substrate (shown in FIG. 1) to prepare a patterned silicon substrate (PSS) 1. Preferably, the present invention can optionally etch the patterned structure by dry etching.

(17) The Si substrate is a Si (111) crystal face or a Si (100) crystal face or a Si (110) crystal face, and the doping type is n-type or p-type.

(18) In the present invention, the patterned structure etched on the Si substrate is not particularly limited, and a corresponding patterned structure can be produced according to design requirements.

(19) Referring to the cross-sectional views and the top views shown in FIG. 2A to FIG. 2G, the patterned structures which can be fabricated on the silicon substrate are various, and only some commonly used pattern structures are listed here, but the present invention is not limited thereto.

(20) On the one hand, the patterned Si substrate can effectively reduce the dislocation density in GaN epitaxial material, improve the crystal quality of epitaxial layer, thereby reducing the non-radiative recombination of active region, reducing the reverse leakage current, and improving the lifetime of the LED; on the other hand, the light emitted by the active region is scattered multiple times by the interfaces between GaN and Al.sub.2O.sub.3 coatings, which changes the exit angle of the total reflected light, and increases the probability that the light of a flip-chipped LED is emitted from the Al.sub.2O.sub.3 coating, thereby improving the light extraction efficiency.

(21) (2) Referring to FIG. 3, an Al.sub.2O.sub.3 coating is grown by molecular beam epitaxy (MBE). Specifically, the patterned Si substrate 1 is first plated with an Al layer having a thickness of 1 nm to 200 nm, and then, an oxygen plasma is introduced to form an Al.sub.2O.sub.3 coating.

(22) In order to avoid melt-back reaction, the LED device structure prepared on the Si substrate must first grow AlN as a nucleation layer, and then grow a GaN epitaxial layer thereon, but the AlN growth mode tends to be in a columnar growth mode, the problem of AlN crystal walls is generated when the layer is patterned on the Si substrate without Al.sub.2O.sub.3 coating, resulting in that a gap exists in the GaN layer, or a thick GaN layer is required in order to be completely combined; and an AlN nucleation layer can be grown on any crystal face, and it is even possible to form a polycrystalline epitaxial film using AlN as a nucleation layer. If Al.sub.2O.sub.3 is used as a coating, the Si substrate can be effectively protected, and the melt-back reaction is avoided, and the GaN nucleation layer can be directly used to realize single crystal growth. The growth rate of GaN is the fastest in (0002) direction, and the growth rate in other directions is suppressed by the growth in the (0002) direction, thereby solving the problem that the GaN crystal grains cannot be effectively combined. In this way, a large-sized Si substrate GaN-based LED can be prepared, which provides a guarantee for developing a high-power Si substrate GaN-based LED device and reducing the price of LED.

(23) (3) A nucleation layer 3 is grown on the Al.sub.2O.sub.3 coating as shown in FIGS. 4A and 4B. FIG. 4A shows that when the width of a groove of the patterned structure on the Si substrate is large, the nucleation layer 3 can be grown onto the inner wall and the bottom of the groove. However, if the width of the groove of the patterned structure on the Si substrate is small, so that atoms cannot enter, as shown in FIG. 4B, the nucleation layer 3 cannot be grown on the inner wall and the bottom of the groove.

(24) In the present invention, the nucleation layer 3 may preferably be AlGaN or GaN.

(25) (4) As shown in FIGS. 5a and 5b, a first buffer layer 4 having a thickness of 100 nm to 5000 nm is epitaxially grown on the nucleation layer 3 by MOCVD. The first buffer layer 4 is preferably GaN.

(26) FIG. 5A corresponds to FIG. 4A. When the groove of the patterned structure is wide, the first buffer layer 4 can be grown onto the side wall and bottom of the groove.

(27) FIG. 5B corresponds to FIG. 4B. When the groove of the patterned structure is narrow, the first GaN buffer layer 4 cannot grow onto the sidewall and bottom of the groove, and the first GaN buffer layer 4 cannot grow onto the portion close to the groove opening.

(28) (5) Referring to FIG. 6, a stress buffer layer is epitaxially grown on the first GaN buffer layer 4 by the MOCVD method. The stress buffer layer can act to regulate stress.

(29) In the present invention, preferably, the stress buffer layer is composed of a first interposer layer 5, a second buffer layer 6, and a second insertion layer 7. However, the present invention is not limited thereto, and the stress buffer layer may be composed of three insertion layers and two buffer layers alternately, or more insertion layers and more buffer layers alternately.

(30) In the present invention, preferably, the first insertion layer 5 and the second insertion layer 7 may be any one of an AlGaN insertion layer, an AlN insertion layer, or a superlattice insertion layer.

(31) The first interposer layer 5 and the second interposer layer 7 have a thickness of 5 nm to 100 nm, and the second buffer layer 6 has a thickness of 100 nm to 5000 nm.

(32) (6) Referring to FIG. 7, the light emitting structure layer is epitaxially grown on the stress buffer layer by the MOVCD method. In the present invention, preferably, the light emitting structure layer is an n-GaN layer 8 of 1 m to 5 m, a quantum well layer 9 with multilayer structure, and a PGaN layer 10 of 0.1 m to 2 m.

(33) (7) Referring to FIG. 8, a welded mirror metal layer 11 is coated on the p-GaN layer by sputtering, metal evaporation or electroplating, which is a silver or magnesium plated aluminum plate or nickel plate, the aluminum plate or nickel plate is bonded to the p-GaN layer 9 to form an ohmic contact.

(34) (8) Referring to FIG. 9, the epitaxial layer is transferred to a new low-resistance double-side-polished Si substrate 12 through a solder metal layer, and a flip-chipping process is used to cause the welded mirror metal layer 11 to reflect light and to emit light from the Al.sub.2O.sub.3 coating.

(35) (9) Referring to FIG. 10, an ohmic contact p-electrode 13 is formed on the Si substrate 12.

(36) Etching is performed from the Si substrate 12 by dry etching until the n-GaN layer 8 is exposed, and a transparent electrode is plated on the exposed n-GaN layer 8, and gold or nickel is sputtered on the transparent electrode and etched into an electrode pattern to form an ohmic contact n-electrode 14.

(37) (10) Referring to FIG. 11, using the Al.sub.2O.sub.3 coating as a barrier layer, the patterned Si substrate 1 is removed by wet etching to expose a patterned Al.sub.2O.sub.3 coating to form an LED device.

(38) Compared with the prior art, the beneficial effects of the present invention are:

(39) 1. The present invention employs a patterned silicon substrate which is easier to fabricate various types of patterns on a Si substrate than a patterned sapphire substrate currently used in the LED industry, and the size and style selection of patterns are also more than that of the sapphire substrate; in addition, the patterned Si substrate has the following advantages: on one hand, the dislocation density of the GaN epitaxial material can be effectively reduced, thereby reducing the non-radiative recombination of active regions, and reducing the reverse leakage current, and increasing the lifetime of LED; on the other hand, the light emitted by the active regions is scattered multiple times by GaN and substrate interfaces, changing the exit angle of the total reflected light, increasing the probability that the flip-chipped LED light will exit the substrate, thereby improving the efficiency of light extraction.

(40) 2. The present invention employs an Al.sub.2O.sub.3 coating on a patterned silicon substrate and then directly grows a GaN or AlGaN nucleation layer. It is necessary for the LED device structure on a conventional Si substrate to first grow AlN as a nucleation layer, and then grow a GaN epitaxial layer thereon, but the AlN growth mode tends to be in a columnar growth mode, the problem of AlN crystal walls is generated when the layer is patterned on a PSS substrate, resulting in a gap exists in the GaN layer, or a thick GaN layer required in order to be completely combined. If GaN or AlGaN is used as the nucleation layer, the problem that GaN crystal grains cannot be effectively combined can be solved. In this way, a large-sized Si substrate GaN-based LED epitaxial wafer can be prepared, which provides a guarantee for developing a high-power Si substrate GaN-based LED device and reducing the price of LED.

(41) 3. Adding a stress buffer layer to the entire LED device structure solves the problem of surface cracking of the epitaxial layer which is caused by the tensile stress caused by the Si substrate when the GaN epitaxial layer is cooled.

(42) It is obvious to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered as exemplary and not limiting in any way, and the scope of the invention is defined by the appended claims rather than the description. Therefore, all changes that come within the meaning and range of equivalents of the claims are intended to be included in the invention. Any reference signs in the claims should not be construed as limiting the claim.

(43) In addition, it should be understood that, although the description is described in terms of embodiments, not every embodiment includes only one independent technical solution. The description of the specification is merely for the sake of clarity, and those skilled in the art should regard the specification. The technical solutions in the respective embodiments may also be combined as appropriate to form other embodiments that can be understood by those skilled in the art.