Patent Application
20140054593
The technical field relates to a nitride semiconductor structure.
Nowadays, it has been proved that Gallium Nitride-based (GaN-based) semiconductor material has potential for the commercial applications to the backlight module of LCD, optical storage system, high frequency and high power microwave electronic device, and so on. As to the epitaxial growth of GaN-based semiconductor material, sapphire substrate is mainly used as substrate.
However, it is a main topic to reduce production cost and to improve film quality in the application of lighting and electronic devices, and therefore, silicon substrate tends to be utilized for cost down. Nevertheless, the derivational issue is the mismatch between nitride and silicon in lattice constant and thermal expansion coefficient, and thus it may cause GaN epitaxial layer to have considerable cracks and tensile stress. Accordingly, the yield of large-size GaN epitaxial chip is too low to reduce production cost.
One of exemplary embodiments comprises a nitride semiconductor structure including a silicon substrate, a MN layer, a AlGaN layer and a GaN layer formed on the AlGaN layer. The silicon substrate has a surface tilted at 0<tilted≦0.5° with respect to a axis perpendicular to a (111) crystal plane. The AlN layer is formed on the surface of the silicon substrate. The AlGaN layer is formed on the AlN layer, and an Al content in the AlGaN layer is decreased gradually in a layer thickness direction from the AlN layer side toward the GaN layer side.
Another of exemplary embodiments comprises a nitride semiconductor structure including a silicon substrate, a AlN layer, a AlGaN layer and a GaN layer formed on the AlGaN layer. The AlN layer is formed on the surface of the silicon substrate. The AlGaN layer is formed on the AlN layer. A variation rate in the lattice constant of the AlGaN layer is from 5.08%/μm to 1.27%/μm.
Several exemplary embodiments accompanied with figures are described in detail below to further describe the disclosure in details.
The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments and, together with the description, serve to explain the principles of the disclosure.
With reference to the drawings attached, the disclosure will be described by means of the embodiments below. Nevertheless, the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, for the purpose of clarity and specificity, the sizes and the relative sizes of each layer and region may not be illustrated in accurate proportion.
Referring to
In the first exemplary embodiment, a sum of the thicknesses of the AlN layer 104, the AlGaN layer 106 and the GaN layer 108 is at least 3 μm. In the exemplary example, a thickness of the AlN layer 104 is about 50-150 nm, and a thickness of the GaN layer 108 is about 0.5-5 μm. When a thickness of the AlGaN layer 106 is from 0.5 μm to 2 μm, a variation rate in the lattice constant of the AlGaN layer 106 is from 5.08%/μm to 1.27%/μm, for example.
The so-called “variation rate in the lattice constant” represents a ratio of the lattice constant variation to the thickness. The lattice constants of (0001) AlN and (0001) GaN in a-axis are 3.11 Å and 3.189 Å, respectively. The variation rate of lattice constant in percentage (%) is equal to
The variation rate of lattice constant divided by the thickness of the AlGaN layer 106 is from 5.08%/μm to 1.27%/μm. The structure having the variation rate in the lattice constant may reduce stress build in epitaxy layer and improve the crystal quality.
Moreover, the surface 102a of the silicon substrate 102 in the first exemplary embodiment may be a flat surface or comprise patterns as shown in
In
A plurality of experimental results is provided below to verify the effect of the exemplary embodiments.
Three single crystal silicon substrates are provided, and each has a surface tilted at 0.5° with respect to a axis perpendicular to the (111) crystal plane. Stacked layers comprising AlN (100 nm)/AlGaN (1200 nm)/GaN (1300 nm) are grown on the tilted surface of the Si substrate by metal organic chemical vapor deposition (MOCVD). The Al content in the AlGaN layer is continuously decreased from 100 at % to 0 at %. The difference between Experimental examples 1-3 is related to the epitaxial growth temperature. In detail, the GaN layers in Experimental examples 1-3 are grown at 1130° C., 1080° C., and 1030° C. respectively. Each GaN layer of Experimental examples 1-3 is then examined. The result is shown in Table 1.
Except for the surface of each single crystal silicon substrate is a (111) silicon substrate, the manufacturing methods of Comparative examples 1-3 are the same as Experimental examples 1-3. Each GaN layer of Comparative examples 1-3 is then examined. The result is shown in Table 1.
Table 1 shows that the FWHM of (102) XRD of GaN layers of Experimental examples 1-3 are significantly decreased in comparison with Comparative examples 1-3. Therefore, the experimental examples 1-3 obtain lower value of FWHM of (102) XRD than the Comparative examples 1-3 while lower value of FWHM of (102) XRD indicates the lower density of threading dislocations and the better crystalline quality.
A (111) silicon substrate is patterned to form rectangular protrusions. In detail, the area of each rectangular protrusion is about 300×300 μm2, the thickness of each rectangular protrusion is about 2 μm, and the interval between the two rectangular protrusions is about 40 μm. Stacked layers comprising MN (100 nm)/multilayered AlGaN (1200 nm)/GaN (1300 nm) are grown on the silicon substrate by MOCVD. The Al content in the multilayered AlGaN layer is decreased stepwise from the MN layer toward the GaN layer, and the multilayered AlGaN layer includes a first thin film with 40 at % Al and 150 nm thick, a second thin film with 30 at % Al and 200 nm thick, a third thin film with 20 at % Al and 400 nm thick, and a fourth thin film with 10 at % Al and 450 nm thick. Through optical microscope (OM),
Except for the silicon substrate is not patterned, the manufacturing method is the same as Experimental example 4. Through optical microscope (OM),
A stacked layer comprising MN (100 nm)/AlGaN (1200 nm)/GaN (1300 nm) is grown on a flat undoped silicon substrate by MOCVD. The Al content in the AlGaN layer is continuously decreased from 100 at % to 0 at %. The GaN layer of Experimental example 5 is then examined. The result is shown in
Except for the silicon substrate having a surface tilted at 0.5° with respect to a axis perpendicular to the (111) crystal plane, the manufacturing method is the same as Experimental example 5. The GaN layer of Experimental example 6 is then examined. The result is shown in
Except for doping phosphorous in the silicon substrate, the manufacturing method is the same as Experimental example 5. The doping concentration is from −1×1015/cm3 to −1×1016/cm3. The GaN layer of Experimental example 7 is then examined. The result is shown in
A stacked layer comprising AlN (100 nm)/AlGaN/GaN (1300 nm) is grown on the (111) silicon substrate. The Al content in the AlGaN layer is decreased continuously in the layer thickness direction from the AlN layer side toward the GaN layer side. In particular, the Al content in the AlGaN layer is continuously decreased from 100 at % to 0 at %. Moreover, the thickness of the AlGaN layer is also varied from 0.3 μm to 2 μm. The GaN layers of Experimental example 8 are then examined. The result is shown in
A stacked layer comprising AlN (100 nm)/multilayered AlGaN (1200 nm)/GaN (1300 nm) is grown on a (111) silicon substrate by MOCVD. The Al content in the multilayered AlGaN layer is decreased stepwise from the AlN layer toward the GaN layer, and the multilayered AlGaN layers includes a first thin film with 40 at % Al and 150 nm thick, a second thin film with 30 at % Al and 200 nm thick, a third thin film with 20 at % Al and 400 nm thick, and a fourth thin film with 10 at % Al and 450 nm thick. Through optical microscope (OM),
Except for the absent of the multilayer AlGaN, the manufacturing method is the same as Experimental example 9. Through OM,
An AlN layer of 100 nm is grown on a (111) silicon substrate and then a multilayer AlGaN layer of 1200 nm is grown on the AlN layer. The multilayer AlGaN layer is the same as that in Experimental example 9. A first AlN interlayer of 10 nm is grown on the multilayer AlGaN layer, and a first GaN film of 750 nm is then grown on the first AlN interlayer. A second AlN interlayer of 10 nm is grown on the first GaN film, and a second GaN film of 1000 nm is then grown on the second AlN interlayer. A third AlN interlayer of 10 nm is grown on the second GaN film, and a third GaN film of 1000 nm is then grown on the third AlN interlayer. Through OM,
In view of the above, the disclosure utilizes a graded AlGaN layer in Al content, and thus the cracks in the GaN layer may be eliminated and the quality of the GaN layer may be improved. Moreover, the disclosure utilizes a silicon substrate having a tilted surface, so the lower density of threading dislocations and the better crystalline quality in the GaN layer may be obtained. In addition, the GaN layer is grown on the doped Si substrate according to the disclosure, and thus the density of threading dislocations therein may be reduced and its crystalline quality may be increased. Furthermore, due to the presence of the AlN interlayers sandwiched by the GaN films, the GaN films in the disclosure tend to crack free.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.
