WO2007076730A1 - GaN-BASED OPTOELECTRONIC DEVICE AND METHOD OF MANUFACTURE THE SAME - Google Patents

Abstract

A GaN-based optoelectronic device and a method of manufacturing the same are disclosed, GaN-based optoelectronic device comprises substrate (100), low temperature buffer layer (110), N-GaN layer (120), quantum well active layer (130), p-AlGaN limiting layer (140) and P-GaN layer (150). The invention uses the MOVPE growth technology, is especially suitable to manufacture light emitting diode. Using the low temperature buffer layer remarkably improve the performance of device, the yield and the reliability, especially for light emitting diode containing thick and heavily doped N-GaN layer.

Description

 Ga-based optoelectronic device and method of manufacturing the same

 The present invention relates to the fabrication of GaN-based optoelectronic devices in a broad sense and related M0CVD growth techniques, particularly the fabrication of light-emitting diodes. Background technique

 It is well known that silicon-doped N-GaN is an important basis for all related optoelectronic devices. Generally, the optical and electrical properties of a device are closely related to the crystal quality of this layer.

 As shown in Figure 1, a conventional light emitting diode includes a sapphire substrate (100) and a set of epitaxial layers grown thereon using M0CVD techniques. These epitaxial layers are composed of the following five layers: a low temperature buffer layer (110), a heavily doped N-type GaN layer (120), an active region (130) composed of a quantum well structure, An AlGaN confinement layer (140), and a P-type GaN layer (150).

 Among all the epitaxial layers, the N-type GaN layer is an important layer, and it mainly functions in the following three aspects. First, it is generally desirable for the N-type GaN layer to have a higher conductivity, which effectively disperses the current and has a lower forward operating voltage and thus lowers power consumption. Second, in a sapphire-based light-emitting diode, the N-GaN layer is also an important light extraction layer, and the emission of light from the side of the N-GaN layer is a major part of the total light output. Because of the difference in refractive index of light, most of the light emitted by the active area cannot escape, so many efforts are required to make the chip emit more light. One of the efforts is to thicken the chip, especially the thickness of the N-type GaN layer, because the extraction rate of light in an ideal state is proportional to the thickness of the N-type GaN layer.

Finally, but most importantly, because the N-type GaN layer is the "ground" layer that was originally grown, the crystal quality of the N-type GaN layer directly affects the performance of subsequent layers. Therefore a high quality residual stress-free N-type GaN layer for high performance Light-emitting diodes are essential.

 However, if conventional single layer GaN is used (see U.S. Patent No. 5,290,393, inventor: Nakamura et al., March 1, 1994) or A1N (see U.S. Patent No. 4,855,249, inventor: Akasaki et al., August 8, 1989) As a low temperature buffer layer on the sapphire substrate, due to lattice mismatch, subsequent M0VPE growth will be difficult to obtain a high quality, thick enough heavily doped N-type GaN layer.

 Since the stress is gradually accumulated during the growth process, when the thickness of the film reaches a certain value, also called the critical thickness, excessive stress will break the crystal bond, resulting in the occurrence of misfit dislocations and the film. Cracked. More seriously, if the doping concentration of the N-type GaN layer is high, such as doping with Si or other impurities, these substitutional impurity atoms will cause further changes in the lattice size, thereby causing the crack to deteriorate, in other words Generally speaking, heavily doped N-type GaN has a smaller critical thickness than an undoped GaN layer.

Usually, due to the difference in lattice mismatch and thermal expansion coefficient, stress release during high temperature growth causes cracking. The heavily doped thicker N-type GaN layer is much more likely to crack than the thinner layer. This situation becomes especially serious if the impurity is Si (the Si atom radius is 30% smaller than the Ga atom it replaces). Under normal circumstances, if the doping concentration of Si is about 5xl 0 ¹⁸ cm- ³ , the N-type GaN layer can be as long as 2 to 3 μm without cracking. However, it should be noted that the critical thickness is also strongly dependent on the growth temperature. The higher the temperature, the smaller the critical thickness.

It is well known that dislocations and cracks are fatal defects in LED devices (see Liu Henghe, et al., Problems in the production of Al InGaN-based LED chips, 2003 SPE Conference Proceedings, Vol. ^4, 996, p. 125). They often lead directly to device failure, typically in the form of partial or even no luminescence. These failures greatly reduce the yield and correspondingly increase the production cost. The significance of these defects will also affect the reliability of the device. They accelerate the aging process and shorten the life of the device, resulting in high failure rates during operation. They are generally not resistant to high voltage electrostatic discharges, which means they may suddenly fail in an electrostatic environment.

Conventional means for reducing cracking include appropriately reducing the doping concentration of silicon, lowering the growth temperature of the N-type GaN layer, and reducing the thickness of the N-type GaN layer. Based on the foregoing discussion, we have known that the disadvantage of reducing the doping concentration is that the resistance of the N-type GaN layer is increased, thereby increasing the forward operating voltage _Vf . At the same time, reducing the thickness of N-type GaN is also very different from the benefits of the thick N-type GaN layer we mentioned earlier. Decreasing the growth temperature of the N-type GaN layer leads to a decrease in electron mobility and an increase in the forward operating voltage.

 In addition, from the perspective of overall device performance, in order to further reduce the forward operating voltage and power consumption, thereby reducing thermal effects and improving device reliability, the process direction should be selected for high temperature growth, thick N-type GaN and high doping concentration. .

 In summary, for a light-emitting diode device grown with M0VPE, since a thick heavily doped N-type GaN layer is indispensable, it is imperative to alleviate the resulting cracking problem, which will not only improve. The performance of the device, the widening of the process conditions window, also allows for better control of the forward voltage and overall improvement in product quality and yield. Summary of the invention

 This invention specifically addresses and addresses the potential problems previously raised with the advantages of heavily doped thick N-type GaN in current GaN-based optoelectronic device fabrication processes.

 The present invention includes devices for growing gallium nitride based using M0VPE technology, and are particularly suitable for use in the fabrication of light emitting diode (LED) devices. The device structure includes a substrate, a low temperature buffer layer, an N-type GaN layer, a quantum well active layer, a P-type AlGaN confinement layer, and a P-type GaN layer.

As noted above, the use of a low temperature buffer layer greatly improves the performance of the device, especially for light emitting diodes that use thicker, high temperature grown heavily doped N-type GaN layers. To further improve the yield and reliability of the protection.

According to an embodiment of the present invention, the present invention relates to an optoelectronic device comprising a substrate and an epitaxial layer, wherein the epitaxial layer comprises: a buffer layer grown on the substrate, an N-type GaN layer grown on the buffer layer, An active layer including a single quantum well or a multiple quantum well over the N-type GaN layer, a P-type AlGaN confinement layer over the active layer, and a P-type GaN layer over the P - -type AlGaN confinement layer, characterized In that the buffer layer consists of one or more layers of doped or undoped In _x G _ai - _x N layers and/or doped or undoped Al _y G _ai — _y N layers, or The buffer layer is AUn _b Ga. The N layer, wherein the X and y values representing the atomic composition of the element are 0 < χ < 1 and 0 < y < 1 respectively; the ranges of a, b, and c representing the atomic composition of the element are 0 < a < l, 0 < b 1 , 0<c < 1 JL a+b+c=l ₀

 According to a further embodiment of the present invention, the present invention is also directed to a method of fabricating the above-described optoelectronic device, characterized in that the epitaxial layer is grown on a substrate by a MOVPE technique, wherein the buffer layer has a growth temperature of 400 to 800°. C; N-type GaN has a growth temperature of 800 ° C to 1300 ° C. DRAWINGS

 BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic cross-sectional view of a conventional gallium nitride based light emitting diode device having a low temperature single layer buffer layer.

 Fig. 2 is a schematic cross-sectional view showing a novel gallium nitride based light emitting diode device having a low temperature composite buffer layer.

贴向衬底一侧） 两层 结构。 图 3A是没有掺杂的， 图 3B则包^了掺杂 （X ) 。 3A and 3B are schematic cross-sectional views of a first type of low temperature composite buffer layer. It includes AlyGanN/InxGa _X N

Attached to the side of the substrate) Two-layer structure. Figure 3A is undoped, and Figure 3B is doped (X).

贴向衬底一侧） 两层 结构。 图 4A是没有掺杂的， 图 4B则包括了掺杂 （X ) 。 图 5A和 5B所展示的是基于第一类低温复合型緩沖层结构的 厚 N-GaN实例相衬显微镜照片。 具体实施方式 4A and 4B are schematic cross-sectional views showing a cyanide type low temperature composite buffer layer. it includes

Attached to the side of the substrate) Two-layer structure. Figure 4A is undoped, and Figure 4B includes doping (X). 5A and 5B show a phase contrast micrograph of a thick N-GaN example based on a first type of low temperature composite buffer layer structure. detailed description

After discussion thread and further illustrate clearly demonstrate the advantages brought by the invention and benefits ₀

 The detailed description and illustrations of the present invention are set forth to provide a more detailed description of the present invention, but are not intended to emphasize that these are the only technical solutions that can be used and implemented. The detailed description of the back-end details the specific steps for growing a gallium nitride device such as a light-emitting diode or the like using the M0VPE technique. It is to be noted, however, that the construction of the same or equivalent functions in other different forms is also within the scope of the invention.

 Moreover, what is discussed directly herein is the growth of a gallium nitride based light emitting diode using the M0VPE technique, which is merely an illustrative method and is not meant to limit the invention to only this technique. It will be readily apparent to those skilled in the art that the invention is equally applicable to other deposition growth processes (e.g., MBE and HVPE). Similarly, the present invention is not only applicable to the fabrication of light-emitting diodes, but also to the fabrication of devices in various other aspects. For example, the present invention can be used to enhance the performance and reliability of other Ga-based devices, including high power microwave devices and ultra high power switching devices.

 The main object of the present invention is to obtain a sufficiently thick high-quality N-type GaN layer by using a novel pre-grown composite low-temperature buffer layer to achieve the purpose of reducing the defect density and preventing cracking. These buffer layers grown at relatively low temperatures (400 ° C to 800 ° C) can effectively release the stresses accumulated by themselves, thereby providing a growth substrate with almost no residual stress and near lattice matching for subsequent needs. An epitaxial layer that grows on it.

The low temperature buffer layer mentioned in the present invention is directly grown on a substrate, such as blue Gem substrate. This layer may be composed of one or more layers of AlyGa- _y N and/or In _x G _ai - _x N layers, and they may appear in different orders, or may have one of silicon, magnesium and carbon. One or more of the incorporation or non-doping. Here, X and y are used to represent the atomic composition of the elements, and they can range from 0 to 1. At the same time, those skilled in the art can adjust the specific composition of each layer according to specific requirements. That is to say, the composition of each layer is not necessarily the same.

的厚度范围优选应控制在 0 ~ 1000埃 （A ) , 而 Al_yG_ai-_yN的厚度范围优选应控制在 0 ~ 2000埃（A ) 。 同时， 本领域技术人员能够根据具体要求调整各层的厚度。 也就是说， 各层的厚度不一定相同。另外， Al_aIn_bGa。N层的厚度范围优选是 0 ~

There is no particular requirement for the thickness of each layer of In _x Ga N and Al _y G _ai - _y N in the composite buffer layer. but,

The thickness range should preferably be controlled from 0 to 1000 angstroms (A), and the thickness range of Al _y G _ai - _y N should preferably be controlled from 0 to 2000 angstroms (A). At the same time, those skilled in the art can adjust the thickness of each layer according to specific requirements. That is to say, the thickness of each layer is not necessarily the same. In addition, Al _a In _b Ga. The thickness of the N layer is preferably 0 ~

 The composite buffer layer is typically grown at a lower temperature, i.e., below the growth temperature of the N-type GaN layer. The ideal growth temperature for N-type GaN is usually about 800 Ό to 1300 °C. The suitable growth temperature of the buffer of the present invention should be 40 (TC to 800)

. C.

层在更普遍意义下可以都是 Al InGaN或都是 Al InGaN掺杂层，而且 Al， Ga， In 在这两层中的 浓度可以是不同的，而掺杂在其中的掺杂物可以是 Si、 Mg和 C中 的一种或两种。 In addition,

The layers may all be Al InGaN or both Al InGaN doped layers in a more general sense, and the concentrations of Al, Ga, In in the two layers may be different, and the dopant doped therein may be Si One or two of Mg, C and C.

The thickness of each layer in the GaN-based photoelectron standard device is preferably as follows: the substrate is about 0.4 mm, the buffer layer is about 20 nm to 300 nm, the N-type GaN layer is about 2 to 5 μm, and the active layer is about 100 nm. The 300 nm, P − -type AlGaN layer is about 25 nm to 250 nm, and the P − -type GaN layer is about 100 nm to 500 nm. However, it will be apparent to those skilled in the art that the above thickness ranges are only preferred ranges, and those skilled in the art will be able to determine the specific thickness of each of the above layers in accordance with the prior art, and the resulting devices are also within the scope of the present invention. There is no particular limitation on the substrate, which may be any substrate that can be used in the present invention, such as, but not limited to, sapphire, Zii0, S i, GaAs, S iC, and the like.

In general, GaN-based light emitting diodes having thicker N-type GaN layers can directly benefit from the present invention. This composite buffer layer helps reduce defect density and prevent cracking. Thereby improving the yield of the product. In addition, this invention for improving the thick N-type GaN layer will further help to optimize the performance of LEDs, which are embodied in the following aspects: First, high-quality thick N-type GaN due to the increase in lateral effective area of the chip The light extraction efficiency is improved, and the lower resistance not only improves the current distribution, but also helps to reduce the forward working voltage V _f and thus the energy loss, thereby enhancing the reliability of the device.

 Figure 1 is a schematic cross-sectional view of a conventional light emitting diode. As previously described, the structure of the light emitting diode includes a sapphire substrate (100) and a series of epitaxial layers grown by M0VPE technology. The epitaxial layer comprises a conventional low temperature buffer layer such as 300 angstroms thick or A1N (110), a heavily doped N-type GaN layer (120), an active layer (130) composed of multiple quantum wells, A P-type AlGaN confinement layer (140) and a P-type GaN layer (150).

 Figure 2 is a schematic cross-sectional view of a novel light emitting diode structure including the present invention. This new diode device includes a sapphire substrate (200) and a series of epitaxial layers grown using M0VPE. The invention includes an InxGa N/AlyGa N composite buffer layer (210), a heavily doped N-type GaN layer (220), an active layer (230) composed of multiple quantum wells, and a P-type An AlGaN confinement layer (240) and a P-type GaN layer (250).

层（41½)。 图 4B 中所示的结构 与次序与 4A—致， 所不同的只是 4B中包含了掺杂（X)， 杂质（X) 可以是硅（S i)、 镁 (Mg)、 碳（C) 等。 The design of the first type of composite buffer layer (310a) of the first type shown in Fig. 3A. The order is to first grow an In _x G _ai - _x N layer (312a) on the sapphire substrate and then regenerate the long AlyGa yN layer (314a). The structure and order shown in FIG. 3B are the same as those of 3A, the only difference being that the doping (X) is contained in 3B, and the impurity (X) may be silicon (S i ), magnesium (Mg), carbon (C), or the like. . Shown in Figure 4A is the design of a second type of composite buffer layer (410a). The arrangement of the growth order is exactly the opposite of the case of FIG. In this structure, Mr. Al _y Ga N layer (412a), then regrowth

Layer (411⁄2). The structure and sequence shown in FIG. 4B are different from those of 4A, except that 4B contains doping (X), and impurity (X) may be silicon (S i ), magnesium (Mg), carbon (C), etc. .

5A and 5B show is based on the thickness of the first instance of the class N-GaN low-temperature buffer layer composite structure with village micrograph user total thickness of about 4.5 microns, doped silicon concentration is about 5xl 0 ¹⁸ Cnf ³ . Figure 5A shows the surface of the sample without optimization, with a set of cracks in one direction, and Figure 5B shows the surface optimized for composition and thickness without any cracks.

 The growth method of each layer of the optoelectronic device of the present invention is well known in the art and is not particularly limited.

In summary, the present invention provides a novel device structure and associated M0VPE growth techniques for overcoming the generation of dislocations and cracks. The invention also improves the performance of the device, broadens the growth window of the N-type GaN layer, enhances the control of the forward voltage _Vf , and changes the product quality and reliability as a whole.

 In contrast to the prior art, the present invention provides a novel composite low temperature buffer layer in place of a conventional single buffer layer for thick N-type GaN layer growth and fabrication of related GaN-based semiconductor devices. .

 This composite buffer layer can effectively axe the stress caused by lattice mismatch and thermal expansion mismatch, thereby reducing the formation of defects and preventing cracking. This method of growing a thick N-type GaN layer can be used for performance improvement and reliability improvement of GaN-based light-emitting diodes. It is also widely used in the fabrication of other GaN-based devices, including high-power microwave devices and switching devices. Embodiment 1 : The first type of composite type low temperature buffer layer

Using sapphire as the substrate, a layer of Mr. M0VPE is used at 500 degrees Celsius. 15。 The thickness of the InxGai- _X N layer, wherein x is 0.15. Then, a layer of about 250 A thick Al _y G _ai - _y N layer is further grown at the same temperature, wherein y is 0. 05. The two layers together form a first type of composite type low temperature buffer layer. After a high temperature tempering of 1100 degrees for 10 minutes, a Ν-type (Al) GaN layer of about 3 μm thick was grown at the same high temperature, wherein the doping concentration of silicon was 5×10 ¹⁸ cnf ³ . The rest of the LED structure (quantum well active region and P-type layer) is grown under normal conditions. The first type of composite low temperature buffer layer is suitable for the fabrication of blue and shorter wavelength light emitting diodes. Example 2: The second type of composite type low temperature buffer layer

Using sapphire as the substrate, a layer of about 100A thick Al _y G _ai - _y N is grown by M0VPE at 500 degrees Celsius, where X is 0. 15. Then continue to grow at the same temperature. 200。 The thickness of the InxGa N layer, where y is 0.02. The two layers together form a second type of composite low temperature buffer layer. After 10 minutes of high temperature tempering at 1100 degrees, a Ν-type (In) GaN layer of about 3 μm thick was grown at the same high temperature, wherein the doping concentration of silicon was 5×10 ¹⁸ cm ⁻³ . The rest of the LED structure (quantum well active region and P-type layer) is grown under normal conditions. The second type of composite low temperature buffer layer is suitable for the fabrication of green and longer wavelength light emitting diodes.

Claims

What is claimed is: 1. An optoelectronic device comprising a substrate and an epitaxial layer, wherein the epitaxial layer comprises:  a buffer layer grown on the substrate,  An N-type GaN layer grown on the buffer layer,  An active layer including a single quantum well or a multiple quantum well over the N-type GaN layer, a P-type AlGaN confinement layer above the active layer,  a P-type GaN layer over the P-type AlGaN confinement layer, Characterized in that the buffer layer consists of one or more layers of doped or undoped InxGa J layers and/or doped or undoped

The layer composition, or the buffer layer is an Al _a In _b Ga _c N layer, wherein the x and y values representing the atomic composition of the element are 0 < x < 1 JL 0 < y < 1 respectively; The ranges of b, c are 0 < a 1, 0 < b < 1 > 0 < c < 1 and a + b + c = 1. 2. The optoelectronic device of claim 1 wherein said buffer layer is comprised of a layer

The layer consists of a layer of Al _y Ga _w N. 3. The optoelectronic device according to claim 1, wherein said buffer layer is composed of a plurality of layers

Layer composition. 4. The optoelectronic device according to claim 3, wherein the plurality of layers of In _x G _ai - _X N and the layers of layers of Al _y Ga _w N are alternately arranged. 5. The optoelectronic device according to claim 1, wherein the buffer layer is an In _x G _ai _J layer. 6. The optoelectronic device of claim 1 wherein the buffer layer is an Al _y G _ai - layer. 7. The optoelectronic device according to claim 1, wherein the buffer layer is an Al _a In _b Ga _c N layer.  8. The optoelectronic device according to claim 1, wherein the substrate is selected from the group consisting of sapphire, Zn0, Si, GaAs or SiC. 9. An optoelectronic device according to claim 8, characterized in that the substrate is sapphire. good 10. The optoelectronic device according to claim 1, wherein the In _x G _ai - _x N layer is attached to the substrate side or the Al _y G _ai - _y N layer is attached to the substrate side. The optoelectronic device according to any one of claims 1 to 4, characterized in that

The layers are doped and the doped state is represented by Si: In _x G _ai - _x N and Si: AlyGa! - yN. 12. An optoelectronic device according to any of claims 1 - 4, characterized in that

_{Both the} layer and the Al _y G _ai - _y N layer are doped, and the doped state is represented by Mg: In _x G _ai - _x N and Mg: Al _y Ga yN. 13. An optoelectronic device according to any of claims 1 - 4, characterized in that said In _x G _ai - _X N layer and

The layers are doped and their doped state is (Si+Mg):

And (Si + Mg): AlyGa - _y N to represent. The optoelectronic device according to any one of claims 1 to 6, wherein the In.Gaj-layer or the Al _y Ga N layer is doped, and the doped state thereof is Si: In.Ga^ Or Si: Al _y Ga _y N to indicate. 15. The optoelectronic device of claim 1 wherein said

The thickness of the layer ranges from 0 to 1000 A. 16. The optoelectronic device according to claim 1, wherein said Al _y G _ai - _y N layer has a thickness ranging from 0 to 2000 A. The optoelectronic device according to claim 1, wherein said Al _a In _b Ga N layer has a thickness ranging from 0 to 2000 A.  The optoelectronic device according to any one of claims 1 to 17, wherein the optoelectronic device is a light emitting diode.  19. The method of fabricating an optoelectronic device as claimed in claim 1, wherein the epitaxial layer is grown on the substrate by a MOVPE technique, wherein the buffer layer has a growth temperature of 400 to 800 ° C; Type GaN has a growth temperature of 800 ° C to 1300 ° C