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Nitride semiconductor device and method for manufacturing the sameNitride semiconductor device and method for manufacturing the same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070170441, Nitride semiconductor device and method for manufacturing the same. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001]This non-provisional application claims priority under 35 U.S.C. .sctn.119(a) of Japanese Patent Applications Nos. 2006-17193 and 2006-23029 filed in Japan on 26 Jan. 2006 and 31 Jan. 2006, respectively, the entire contents of which are hereby incorporated by reference. BACKGROUND OF THE INVENTION [0002]1. Field of the Invention [0003]The present invention relates to a nitride semiconductor device using a nitride semiconductor and a method for manufacturing the same. [0004]2. Description of Related Art [0005]A semiconductor light emitting device using a nitride semiconductor has already been practically used as a light emitting diode in various kinds of fields because it is able to emit light over wide wavelength ranges from ultraviolet to blue or green visible light by suitably controlling the composition of the nitride semiconductor. [0006]As the nitride semiconductor has a large band gap and a deep acceptor level, it is difficult to reduce the resistance of a p-type layer. However, in order to reduce the operating voltage of a light emitting diode having a p-n junction, it is essential to reduce the resistance of the p-type layer and contact resistance between the p-type layer and an ohmic electrode. [0007]Hereinafter, as a first conventional example, a light emitting diode using a nitride semiconductor is explained with reference to drawings (see, for example, Shuji Nakamura et al., "Superbright green InGaN single-quantum-well-structure light-emitting diodes", Jpn. J. Appl. Phys. Vol. 34 (1995) L.1332-L.1335). [0008]FIG. 14 shows the sectional structure of the first conventional example of the light emitting diode using a nitride semiconductor. As shown in FIG. 14, the conventional light emitting diode includes a sapphire substrate 101 having a (0001) plane as a principal surface. On the principal surface of the sapphire substrate 101, a GaN buffer layer 102 which grows at low temperatures, an n-type GaN layer 103, an InGaN quantum well active layer 104, a p-type cladding layer 105 made of p-type AlGaN and a p-type contact layer 106 made of p-type GaN are formed in this order. A p-type electrode 107 is formed on the p-type contact layer 106 and an n-type electrode 108 is formed on a selectively exposed part of the n-type GaN layer 103. [0009]In the first conventional example, the p-type cladding layer 105 contains magnesium (Mg) as p-type dopants and heat treatment is carried out in nitrogen atmosphere to obtain a p-type semiconductor layer. [0010]As a second conventional example of a semiconductor device using the nitride semiconductor, a blue-violet semiconductor laser device has already come into practical use. Commonly used blue-violet semiconductor laser devices have a ridge waveguide structure as disclosed by Shuji Nakamura et al., "InGaN/GaN/AlGaN-based laser diodes with modulation-doped strained-layer superlattices grown on an epitalixally laterally overgrown GaN substrate", Appl. Phys. Lett. Vol. 72 (1998) pp. 211-213. In this structure, a p-type semiconductor layer on an active layer is patterned into a convex stripe in order to narrow a current flow and trap emitted light. The blue-violet semiconductor laser device is achieved by a relatively easy process. [0011]However, the light emitting diode using the nitride semiconductor of the first conventional example has limitations in reducing the resistance of the p-type contact layer 106 and the contact resistance between the p-type contact layer 106 and the p-type electrode 107. Therefore, it is difficult to reduce the operating voltage to a further extent. Likewise, it is not easy to reduce the resistance of the p-type contact layer in the semiconductor laser device using the nitride semiconductor. Thus, difficulty remains in improving characteristics, efficiency and reliability of the laser device. [0012]In the semiconductor laser device using the nitride semiconductor of the second conventional example, the ridge waveguide structure having a convex section is provided by dry etching. Therefore, it is difficult to control the thickness of parts of the p-type semiconductor layer remaining on the sides of the ridge. This leads to variations in threshold current in the semiconductor laser device and variations in angle of light emission. [0013]Moreover, since the p-type semiconductor layer is made of a nitride semiconductor which is not suitable for easily producing a low resistance p-type semiconductor layer, the series resistance of the p-type semiconductor layer is increased. Further, electrooptic characteristics and reliability of the laser device may possibly deteriorate due to damage caused by the dry etching for forming the ridge. Thus, the semiconductor laser device of the second conventional example has limitations in improving yield and reducing the operating voltage. SUMMARY OF THE INVENTION [0014]In order to solve the above-described conventional problems, the present invention makes it possible to reduce the resistance of the p-type contact layer and produce a semiconductor laser device having a current confining structure without patterning the p-type semiconductor layer into ridge shape. [0015]In order to achieve the above-described object, the present invention provides a nitride semiconductor device by selectively growing a second nitride semiconductor layer on the side surfaces of a convex portion of a first nitride semiconductor layer. [0016]To be more specific, the nitride semiconductor device of the present invention includes: a substrate having a principal surface; a first nitride semiconductor layer formed on the principal surface of the substrate and includes one or more convex portions whose side surfaces are vertical to the principal surface; and a second nitride semiconductor layer selectively grown on the side surfaces of the one or more convex portions of the first nitride semiconductor layer. [0017]In the nitride semiconductor device of the present invention, the second nitride semiconductor layer is selectively grown on the side surfaces of the one or more convex portions using an organic nitride material. As described later, the thus-formed second nitride semiconductor layer improves the activation rate of p-type dopants and reduces the resistance thereof. [0018]If the conventionally used current confining structure provided on a p-type semiconductor layer formed on an active layer is replaced with the first nitride semiconductor layer of the present invention having the one or more convex portions and n-type conductivity, the need of patterning the p-type semiconductor layer into ridge shape is eliminated. As a result, a large region of the p-type semiconductor layer is surely kept for current injection. This makes it possible to reduce the series resistance and the operating voltage of the device to a notable degree. [0019]As to the nitride semiconductor device of the present invention, it is preferable that the side surfaces of the one or more convex portions are provided by forming protrusions and depressions in at least a top portion of the first nitride semiconductor layer, the first and second nitride semiconductor layers have a p-type conductivity and the second nitride semiconductor layer has a higher p-type carrier concentration than the first nitride semiconductor layer. [0020]This configuration makes it possible to reduce the resistance of the p-type second nitride semiconductor layer. [0021]As to the nitride semiconductor device of the present invention, it is preferable that the side surfaces of the one or more convex portions are provided by forming protrusions and depressions in at least a top portion of the first nitride semiconductor layer, the first and second nitride semiconductor layers have a p-type conductivity and the second nitride semiconductor layer has a lower residual hydrogen concentration than the first nitride semiconductor layer. Continue reading about Nitride semiconductor device and method for manufacturing the same... Full patent description for Nitride semiconductor device and method for manufacturing the same Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Nitride semiconductor device and method for manufacturing the same patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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