Patent Publication Number: US-2010109017-A1

Title: GaN-BASED COMPOUND SEMICONDUCTOR DEVICE

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2005-0033197, filed on Apr. 21, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     The present disclosure relates to a gallium nitride (GaN)-based compound semiconductor device, and more particularly, to a GaN-based compound semiconductor device having a structure improving a surface characteristic of a thin film growing on a substrate. 
     2. Description of the Related Art 
     In a conventional nitride-based semiconductor thin film grown on a heterogeneous substrate defects may be generated due to differences in lattice parameters, which degrade the characteristics of a device. Accordingly, it is essential to use a low-defect GaN substrate for growing a thin film of a nitride-based semiconductor device. However, the thin film growth on a GaN substrate has problems of irregular surface morphology, such as hillocks, crystallinity of a thin film, etc. In particular, generation of hillocks causes segregation of a certain component in a composition of a thin film growing on the hillock, so that the properties of a device are degraded, the manufacturing process for the thin film device becomes difficult, and thus yield is decreased. 
     Accordingly, when a thin film for a optoelectronic device is grown using a GaN substrate, technologies need to be developed for maintaining or improving a surface characteristic by improving surface morphology of the thin film growing in the substrate. 
     SUMMARY OF THE DISCLOSURE 
     The present invention may provide a gallium nitride (GaN)-based compound semiconductor device having a structure for improving a surface characteristic of a thin film growing on a substrate. 
     According to an aspect of the present invention, there is provided a GaN-based compound semiconductor device including an Al x In y Ga 1−x−y N substrate (0≦x≦1, 0≦y≦1, and 0≦x+y≦1) whose surface inclines toward a predetermined direction at an off-angle of greater than 0° and less than 1° to the ( 0001 ) plane, and a GaN-based compound semiconductor layer grown on the surface of the substrate. Here, the substrate can be doped with n-type or p-type impurities. The predetermined direction may be the &lt; 11 - 20 &gt; direction or the &lt; 1 - 100 &gt; direction, in which case the off-angle of the surface of the substrate may be greater than or equal to 0.01° and less than 1°. 
     According to another aspect of the present invention, there is provided a GaN-based compound semiconductor device including an Al x In y Ga 1−x−y N substrate (0≦x≦1, 0≦y≦1, and 0≦x+y≦1) whose surface inclines toward a predetermined direction at an off-angle of greater than 0° and less than or equal to 10° with respect to a plane perpendicular to a non-polar direction, and a GaN-based compound semiconductor layer grown on the surface of the substrate. The plane perpendicular to the non-polar direction is one of the ( 11 - 20 ) plane, the ( 1 - 100 ) plane and the ( 1 - 102 ) plane. The substrate can be doped with n-type or p-type impurities. Preferably, the off-angle of the surface of the substrate is greater than or equal to 0.1° and less than or equal to 1°. 
     According to the present invention having the above-described construction, there is provided a GaN-based compound semiconductor device having excellent device characteristics by improving a surface characteristic of a thin film growing on a substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention are described in detail in exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a schematic perspective view of a gallium nitride (GaN)-based compound semiconductor device according to a first embodiment of the present invention; 
         FIG. 2  is a detailed view of  FIG. 1 ; 
         FIGS. 3A through 3C  are optical interference microscope photographs showing the surface morphology of thin films growing at each surface off-angle on a substrate; 
         FIG. 4  is a schematic perspective view of a laser diode (LD) using a GaN-based compound semiconductor device according to a first embodiment of the present invention; 
         FIG. 5  is a schematic perspective view of a GaN-based compound semiconductor device according to a second embodiment of the present invention; and 
         FIG. 6  is a detailed view of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, a gallium nitride (GaN)-based compound semiconductor device according to the present invention will now be described with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. In the description, the thicknesses of layers and portions illustrated in the figures are exaggerated for clarity of the specification. 
       FIG. 1  is a schematic perspective view of a gallium nitride (GaN)-based compound semiconductor device according to a first embodiment of the present invention, and  FIG. 2  is a detailed view of  FIG. 1 . 
     Referring to  FIGS. 1 and 2 , the GaN-based compound semiconductor device according to the first embodiment of the present invention includes an Al x In y Ga 1−x−y N substrate  11  (0≦x≦1, 0≦y≦1, and 0≦x+y≦1) and a GaN-based compound semiconductor layer  20  grown on the surface of the substrate  11  by metal-organic chemical vapor deposition (MOCVD). The Al x In y Ga 1−x−y N substrate  11  may be doped with n-type or p-type impurities. The surface of the substrate  11  inclines toward a predetermined direction at an off-angle of greater than 0° and less than 1° with respect to the ( 0001 ) plane. The predetermined direction may be the &lt; 11 - 20 &gt; direction or the &lt; 1 - 100 &gt; direction. 
     The GaN-based compound semiconductor layer  20  is a material layer made of Al x In y Ga 1−x−y N (0≦x≦1, 0≦y≦1, and 0≦x+y≦1), formed as a monolayer or a multi-layer on the substrate  11  to construct a unit device. For example, the GaN-based compound semiconductor layer  20  may include an n-type cladding layer  21 , an n-type light guide layer  22 , a multiple quantum well active layer (MQW)  23 , a p-type light guide layer  24  and a p-type cladding layer,  25 , sequentially stacked on the substrate  11 . The n-type cladding layer  21  and the p-type cladding layer  25  are formed of n-type aluminum-gallium-nitride (AlGaN) and p-type AlGaN, respectively. Also, the n-type light guide layer  22  and the p-type light guide layer  24  are formed of n-type GaN and p-type GaN, respectively. The MQW  23  includes a well layer formed of indium-gallium-nitride (InGaN) and a barrier layer formed of GaN or InGaN. 
     For the present invention having such constructions, the off-angle of the surface of the substrate  11  with respect to the ( 0001 ) plane is controlled to be in the range of 0° through 1°, to thereby obtain three different types of surface morphology for the GaN-based compound semiconductor layer  20  according to the off-angle. For example, by substituting “θ” for the off-angle, three different kinds of surface morphology, i.e. a hillock surface, a wavy surface and a mirror-like surface, are obtained in the range of 0°&lt;θ≦0.1°, 0.1°&lt;θ≦0.4°, and 0.4°&lt;θ&lt;1.0°, respectively. Preferably, the off-angle is controlled to be in the range of 0.1° through 1.0°, to thereby obtain a GaN-based compound semiconductor layer without the hillock surface. More preferably, the off-angle is controlled to be in the range of 0.4° through 1.0°, to thereby obtain a mirror-like surface of the GaN-based compound semiconductor layer without having the hillock and wavy surface. 
     According to the present invention, when the GaN-based compound semiconductor layer  20  grows on the Al x In y Ga 1−x−y N substrate  11 , problems caused by generation of irregular surface morphology such as hillocks on the GaN-based compound semiconductor layer  20  can be reduced by controlling the off-angle of the substrate  11 . In particular, the occurrence of indium segregations in an InGaN quantum well near the hillock can be reduced. Accordingly, by improving a surface characteristic of a thin film growing on the substrate  11 , a GaN-based compound semiconductor device having excellent device characteristics can be obtained. 
       FIGS. 3A through 3C  are optical interference microscope photographs showing the surface morphology of thin films growing on a substrate at each surface off-angle. 
       FIGS. 3A through 3C  show surfaces of GaN-based compound semiconductor layers grown on nitride-based semiconductor substrates at off-angles of 0.019°, 0.35° and 0.42°, showing formations of a hillock surface, a wavy surface and a mirror-like surface, respectively. 
       FIG. 4  is a schematic perspective view of a laser diode (LD) using a GaN-based compound semiconductor device according to the first embodiment of the present invention. Compared to the first embodiment in  FIG. 2 , a p-type contact layer  26  formed of p-type GaN is further stacked on the p-type cladding layer  25 . In addition, the p-type cladding layer  25  and the p-type contact layer  26  are etched to a predetermined depth, and their side surfaces are covered with a protective insulative film  27 . Moreover, a p-side electrode  28  and an n-side electrode  31  are prepared on the p-type contact layer  26  and the bottom surface of the Al x In y Ga 1−x−y N substrate  11 , respectively. The p-side electrode  28  and the n-side electrode  31  are nickel/gold (Ni/Au) and titanium/Aluminum (Ti/Al), respectively. 
       FIG. 5  is a schematic perspective view of a GaN-based compound semiconductor device according to a second embodiment of the present invention and  FIG. 6  is a detailed view of  FIG. 5 . Here, explanations for the same components as in the first embodiment shown in  FIGS. 1 and 2  will be omitted, and the same reference numerals will be used. 
     Referring to  FIGS. 5 and 6 , a GaN-based compound semiconductor device according to the second embodiment of the present invention includes an Al x In y Ga 1−x−y N substrate  12  (0≦x≦1, 0≦y≦1, and 0≦x+y≦1) and a GaN-based compound semiconductor layer  20  grown on the substrate  12  by MOCVD. The Al x In y Ga 1−x−y N substrate  12  may be doped with n-type or p-type impurities. The surface of the substrate  12  inclines toward a predetermined direction at an off-angle of greater than 0° and less than or equal to 10° with respect to any one of the planes perpendicular to a non-polar direction, such as the ( 11 - 20 ) plane, the ( 1 - 100 ) plane and the ( 1 - 102 ) plane. The off-angle of the surface of the substrate  12  may be greater than or equal to 0.1° and less than or equal to 1°. The predetermined direction includes all directions existing on any one of the planes perpendicular to the non-polar direction, such as the ( 11 - 20 ) plane, the ( 1 - 100 ) plane and the ( 1 - 102 ) plane. For example, when the substrate  12  has an off-angle with respect to the ( 1 - 100 ) plane, the predetermined direction may be a &lt; 0001 &gt; direction existing on the ( 1 - 100 ) plane. 
     For the present invention having such constructions, the off-angle of the substrate  12  with respect to any one of the planes perpendicular to the non-polar direction, such as the ( 11 - 20 ) plane, the ( 1 - 100 ) plane and the ( 1 - 102 ) plane, is controlled in the range of 0° through 10°, to thereby obtain three different kinds of surface morphology, i.e. the hillock surface, the wavy surface and the mirror-like surface of the GaN-based compound semiconductor layer  20  according to the off-angle, and the effects thereof are described above. 
     According to the present invention having the above-described construction, the problems caused by generation of irregular surface morphology such as hillocks on the GaN-based compound semiconductor layer growing on the substrate can be reduced. Accordingly, a GaN-based compound semiconductor device having excellent device characteristics can be obtained by improving a surface characteristic of a thin film growing on a substrate. 
     The GaN-based compound semiconductor device according to the present invention can be applied to optoelectronic devices such as a light emitting diode (LED), a laser diode (LD), and a photodetector, or other electronic devices. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood that the invention should, however, not be construed as being limited to the embodiments set forth herein; rather, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.