| Light emitting device structure having nitride bulk single crystal layer -> Monitor Keywords |
|
|
  Light emitting device structure having nitride bulk single crystal layerUSPTO Application #: 20060138431Title: Light emitting device structure having nitride bulk single crystal layer Abstract: The object of this invention is to provide a high-output type nitride light emitting device. The nitride light emitting device comprises an n-type nitride semiconductor layer, a p-type nitride semiconductor layer and an active layer therebetween, wherein the light emitting device comprises a gallium-containing nitride semiconductor layer prepared by crystallization from supercritical ammonia-containing solution in the nitride semiconductor layer. (end of abstract) Agent: Westerman, Hattori, Daniels & Adrian, LLP - Washington, DC, US Inventors: Robert Dwilinski, Roman Doradzinski, Jerzy Garczynski, Leszek Sierzputowski, Yasuo Kanbara USPTO Applicaton #: 20060138431 - Class: 257079000 (USPTO) Related Patent Categories: Active Solid-state Devices (e.g., Transistors, Solid-state Diodes), Incoherent Light Emitter Structure The Patent Description & Claims data below is from USPTO Patent Application 20060138431. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a structure wherein a single crystal nitride layer prepared by crystallization from supercritical ammonia-containing solution is used as a substrate or an intermediate layer of light emitting devices such as a laser structure etc. BACKGROUND ART [0002] In the nitride semiconductor laser, crystal defect or dislocation of a waveguide causes electron-hole pairs to make non-radiative recombination therein. Ideally, considering the laser function, the dislocation density in the waveguide may be 10.sup.6/cm.sup.2 or less, preferably 10.sup.4/cm.sup.2 or less. However, in the present situation, the dislocation density can not be reduced to less than 10.sup.6/cm.sup.2 by using a vapor phase epitaxial growth (MOCVD and HVPE) or by using a repeated ELOG (Epitaxial lateral overgrowth), because the waveguide is grown on a heterogeneous substrate, such as sapphire substrate or SiC substrate. [0003] To form a light emitting device comprising nitride semiconductor on a sapphire substrate or a SiC substrate without crack, the nitride semiconductor having the reduced dislocation density is required to be grown in the form of a thin layer on a sapphire substrate or a SiC substrate. If the nitride semiconductor is grown in the form of a thick layer on the substrate such as sapphire substrate etc, the curving of the substrate will be bigger, which leads to higher probability of crack occurrence. However, the nitride semiconductor in the form of a thin layer, in which the dislocation density is reduced, has not been realized by the vapor phase epitaxial growth. [0004] To summarize the above, there has been a limitation to form a nitride semiconductor light emitting device (especially a laser device) by the vapor phase growth. Moreover, regarding the light emitting diode, in case that the higher luminance and higher output are required, the crystal dislocation of the substrate and of the intermediate layer will be a serious problem. DISCLOSURE OF INVENTION [0005] The first object of the present invention is to provide a light emitting device structure, which comprises a light emitting device comprising an n-type nitride semiconductor layer, an active layer comprising an In-containing nitride semiconductor, and a p-type nitride semiconductor layer, formed on a substrate for growth, wherein the light emitting device comprises a gallium-containing nitride semiconductor layer prepared by crystallization from supercritical ammonia-containing solution, instead of the so-far used vapor phase growth. The gallium-containing nitride semiconductor layer as one of the layers in the light emitting device is prepared by crystallization from supercritical ammonia-containing solution so that the crystalline quality of the layers formed on the gallium-containing nitride semiconductor layer can be recovered. [0006] The second object of the present invention is to form a substrate for growth having low dislocation density by using a gallium-containing nitride bulk single crystal prepared by crystallization from supercritical ammonia-containing solution. Accordingly, the nitride semiconductor device formed on the substrate can be a nitride semiconductor with lower dislocation density. Concretely, this object is to form a nitride substrate having a lower dislocation density, i.e. 10.sup.5/cm.sup.2 or less and more preferably 10.sup.4/cm.sup.2 or less and to form thereon a light emitting device (laser structure etc.) having less crystal dislocation causing non-radiative recombination. [0007] The third object of the present invention is to provide a light emitting device structure, such as a laser device etc, which comprises a high-resistance layer prepared by crystallization from supercritical ammonia-containing solution as a current confinement layer. [0008] The inventors of the present invention found the following matters by using a technique wherein a gallium-containing nitride is recrystallized by crystallization from supercritical ammonia-containing solution, so-called AMMONO method: [0009] the ratio of Ga/NH.sub.3 can remarkably be improved (over 20 times), compared with the ratio set by MOCVD vapor phase growth, [0010] the bulk single crystal having a lower dislocation density can be obtained by AMMONO method at a very low temperature (600.degree. C. or less), while the bulk single crystal is prepared by the vapor phase growth of the nitride at 1000.degree. C. or more, [0011] the lower dislocation density and recovery of the crystalline quality thereof can be realized despite the thin layer growth of the gallium-containing nitride, and [0012] the single crystal substrate wherein the single crystal substrate is formed on A-plane or M-plane as an epitaxial growth face can be obtained, while such substrate would not be prepared by the so-far vapor phase growth. [0013] The first invention is to provide a light emitting device structure comprising a gallium-containing nitride single crystal substrate, an n-type nitride semiconductor layer, an active layer comprising an In-containing nitride semiconductor, and a p-type nitride semiconductor layer, formed on the substrate, for growth prepared by the vapor phase growth, wherein a gallium-containing nitride semiconductor layer is formed to preserve the crystalline quality which would be degraded during the deposition of the layers in the light emitting device in the form of quaternary or ternary compound, such as InAlGaN, InGaN or AlGaN etc. on the substrate. Moreover, it is possible to recover the crystalline quality which would be detracted by newly occurred dislocation or impurity dopants during the depositing process of nitride semiconductor. The first invention is characterized in that the gallium-containing nitride semiconductor layer is formed by crystallization from supercritical ammonia-containing solution, so that the layer can become an epitaxial growth plane whose dislocation density thereon is 10.sup.6/cm.sup.2 or less, preferably 10.sup.4/cm.sup.2. [0014] Specifically, the gallium-containing nitride has to be grown at the temperature which does not damage the active layer comprising an In-containing nitride semiconductor. In the AMMONO method, the nitride is grown at 600.degree. C. or less, preferably 550.degree. C. or less, therefore the single crystal GaN or AlGaN layer can be deposited on the active In-containing layer without the detraction of the active layer, although the growth temperature of 1000.degree. C. or more is required in the vapor phase growth. The active layer comprising an In-containing nitride semiconductor is usually formed at 900.degree. C., as lower temperature does not damage to the active layer from degradation etc. Furthermore, the crystalline quality can be recovered by the thin layer of less than several am, preferably several hundreds .ANG. and the dislocation density can also be reduced, so that the resulting laser device etc. is not subject to the stress. [0015] The second invention is characterized in that the substrate is the gallium-containing nitride bulk single crystal prepared by crystallization from supercritical ammonia-containing solution, which leads to a light emitting device with lower dislocation density by the combination of the first invention and the second invention. Moreover, the substrate in the light emitting device structure has at least one plane selected from the group comprising A-plane, M-plane, R-plane, C-plane, {1-10n (n is a natural number)}, and {11-2m (m is a natural number)} of the gallium-containing nitride bulk single crystal, as its own surface. [0016] According to the present invention, a nitride bulk single crystal shown in Drawings can be prepared by applying the AMMONO method, therefore A-plane or M-plane which is parallel to C-axis of hexagonal structure for an epitaxial growth can be obtained. (FIG. 9) In the present invention, an epitaxial growth required by a device structure can be carried out in case that the plane has the area of 100 mm.sup.2. A-plane and M-plane are non-polar, unlike C-plane. In case that A-plane or M-plane of the gallium-containing nitride is used as a plane for depositing of layers, there can be obtained a laser device having no cause of the deterioration of the performance such as the red shift of light emitting, recombination degradation and increase of the threshold current. According to the present invention, when the nitride semiconductor laser device is grown on A-plane of the GaN substrate prepared by crystallization from supercritical ammonia-containing solution, the active layer of the laser device is not subject to the polarization effect. In such a case, the light emitting face of the resonator will be M-plane, on which M-plane end face film can be formed and thus cleavage is easily performed. In case that the nitride semiconductor laser device is grown on M-plane of the GaN substrate prepared by crystallization from supercritical ammonia-containing solution, the active layer is not subject to the polarization effect and A-plane end face film being non-polar can be obtained on the light emitting face of the resonator. [0017] According to the present invention, a substrate for growth means not only a substrate of only gallium-containing nitride but also a composite substrate (template) which comprises gallium-containing nitride grown on a heterogeneous substrate. In case that the gallium-containing nitride is formed on a heterogeneous substrate by crystallization from supercritical ammonia-containing solution, first GaN, AlN or AlGaN layer is preformed on the heterogeneous substrate and then the gallium-containing nitride is formed thereon. [0018] The third invention is characterized by a light emitting device structure which comprises a light emitting device comprising an n-type nitride semiconductor layer, an active layer comprising an In-containing nitride semiconductor, and a p-type nitride semiconductor layer, formed on a substrate for growth, wherein the light emitting device comprises a layer in the form of high-resistance single crystal having a general formula Al.sub.xGa.sub.1-xN (0.ltoreq.x.ltoreq.1), prepared by crystallization from supercritical ammonia-containing solution as a current confinement layer. Accordingly, it is possible to limit the flowing position of the electric current and confine the current without forming the ridge in the laser device. Higher mixture ratio of Al in the crystal leads to the lower refraction index so as to confine the light efficiently. The current confinement layer made of AlN is preferred. [0019] According to the present invention, aforementioned single crystal layer is usually in the form of a non-doped crystal. Even if AlGaN layer has non-uniform mixture ratio of crystal in direction of the thickness and then a tendency of decreased mixture ratio from the beginning of forming step is shown, there is no hindrance to the function as a current confinement layer. Furthermore, the layer can attain its function in the form of thin layer, i.e. several to several tens nm. Accordingly, when the AMMONO method is applied, alkali metal such as Na, K or Li etc, or alkali metal compound such as azide, amide, imide, amide-imide or hydride may be used as a mineralizer. Considering dissolving of the current confinement layer with the supercritical ammonia at the beginning of the AMMONO method, it is preferable that the thickness of the lower layer of the current confinement layer is set thicker than usual. When the current confinement layer or gallium-containing nitride semiconductor layer is prepared by the AMMONO method, it is recommended that a mask may be formed having the lower or same solubility in the supercritical ammonia. The formation of the mask can prevent the dissolution in the supercritical ammonia from the end face of the other layers of the nitride semiconductor, especially the dissolution of the active layer. The mask may be selected from the group consisting of SiO, SiN, AlN, Mo, W, and Ag. In the supercritical ammonia these materials for mask are more stable than GaN and the contact surface covered with the mask material can be prevented from the dissolution. In a later process, i.e. the process of formation of a ridge, the mask can be easily removed. [0020] In the AMMONO method using the supercritical ammonia, a nitride semiconductor is grown in the supercritical ammonia wherein a gallium-containing nitride has the negative solubility curve. Detailed explanation of the method is disclosed in Polish Patent Application Nos. P-347918, P-350375 and PCT Application No. PCT/IB02/04185, so that those skilled in the art can easily carry out the present invention with reference to the abstract and examples explained below. [0021] In the present invention, gallium-containing nitride or nitride is defined as below and as the general formula Al.sub.xGa.sub.1-x-yIn.sub.yN, where 0.ltoreq.x<1, 0.ltoreq.y<1, and 0.ltoreq.x+y<1, and may contain a donor, an acceptor, or a magnetic dopant, as required. For example, if the donor is doped, the nitride can be changed into n-type, so that the gallium-containing nitride semiconductor layer can be formed on a part of n-type nitride semiconductor layer. If acceptor is doped, the nitride can be changed into p-type, so that the gallium-containing nitride semiconductor layer is formed on a part of p-type nitride semiconductor layer. If a substrate for growth is a conductive substrate, a laser device (FIG. 1) or LED device (FIG. 4) having a pair of opposite electrodes can be obtained. It enables to introduce the huge electric current thereto. Continue reading... Full patent description for Light emitting device structure having nitride bulk single crystal layer Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Light emitting device structure having nitride bulk single crystal layer patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Light emitting device structure having nitride bulk single crystal layer or other areas of interest. ### Previous Patent Application: Heteroisomer boron carbide devices Next Patent Application: Optical combiner/decombiner with reduced insertion loss Industry Class: Active solid-state devices (e.g., transistors, solid-state diodes) ### FreshPatents.com Support Thank you for viewing the Light emitting device structure having nitride bulk single crystal layer patent info. IP-related news and info Results in 2.68224 seconds Other interesting Feshpatents.com categories: Software: Finance , AI , Databases , Development , Document , Navigation , Error |
||
