Abstract:
A device includes: a substrate; and a doped III-V compound layer disposed over the substrate; wherein: the doped III-V compound layer includes an upper boundary; the upper boundary has a micro-roughened texture and a macro-roughened texture where the micro-roughened texture located on; and the upper boundary includes dopant ions that are not present in a remainder of the doped III-V compound layer underneath the upper boundary.

Description:
PRIORITY DATA 
     The present application is a divisional of U.S. patent application Ser. No. 13/112,046, filed on May 20, 2011, now U.S. Pat. No. 8,906,712, issued Dec. 9, 2014, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates to light-emitting diode (LED) semiconductor light sources, and fabrication thereof. 
     LEDs are used in diverse lighting applications and can be used to provide radiation across the visible, ultraviolet and/or infrared wavelengths. Such applications include displays, printers, communications, and optoelectronic computer interconnects. One type of LED is a III-V group compound semiconductor LED element, for example, a GaN-LED. However, obtaining sufficient brightness from a GaN-LED, and LEDs in general, has been a challenge. Therefore, what is desired is an LED and process of fabrication of an LED that increases the maximum radiation (e.g., light) output or efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a cross-sectional view of an embodiment of a vertical structure GaN-LED including a surface according to aspects of the present disclosure. 
         FIG. 2  is a cross-sectional view of an alternative embodiment of a vertical structure GaN-LED including a surface according to aspects of the present disclosure. 
         FIG. 3  is a flow chart illustrating an embodiment of a method of fabricating an LED according to aspects of the present disclosure. 
         FIGS. 4-8  illustrate cross sectional views of an embodiment of an LED corresponding to one or more of the steps of the method of  FIG. 3 . 
         FIG. 9  is a graphical representation of an embodiment of the depth of the amorphous/crystal interface at a plurality of implantation conditions. 
     
    
    
     DETAILED DESCRIPTION 
     It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Various features may be arbitrarily drawn in different scales for simplicity and clarity. Furthermore, to the extent the present disclosure illustrates embodiments of vertical structure GaN LEDs, one of ordinary skill in the art would recognize the benefits of the methods discussed herein as applied to other types of LEDs. 
     Illustrated in  FIG. 1  is a light-emitting diode (LED) element  100 . The LED element  100  is a vertical structure GaN-LED, however other configurations are possible. The LED element  100  may be a completed LED product, or portion thereof, or provided during one or more stages of fabrication. The LED element  100  includes a substrate  102 . A plurality of layers (e.g., a stack) is disposed on the substrate  102 . The layers include a GaN layer  104 , a A 1 GaN layer  106 , a multiple quantum well (MQW) layer  108 , a GaN layer  110 , and an electrode  114 . The GaN layer  104  may be a p-type layer (p-GaN). The A 1 GaN layer  106  may be a p-type layer (e.g., having p-type conductivity) (p-AlGaN). The GaN layer  110  may be n-type (e.g., n-type conductivity) (n-GaN). The substrate  102  may include sapphire, oxide monocrystalline, SiC, silicon, ZnO, GaAs, MgAl 2 O 4 , and/or other suitable material. The substrate  102  may include further layers such as, for example, buffer layers, intermediate layers, reflective layers, and/or other suitable layers. The electrode  114  provides an ohmic contact layer and may include various electrically conductive materials. The electrode  114  may be an n-side electrode. Any one of the layers  104 ,  106 ,  108 , and/or  110  may be epitaxially grown or formed by other suitable methods. 
     The LED element  100  has a treated surface  112 . The treated surface  112  is disposed on and/or in the GaN layer  110 . In an embodiment, the treated surface  112  includes the top surface region of a n-GaN layer. The treated surface  112  has a roughened surface property or texture. The treated surface  112  having improved roughness, provides for improved radiation (e.g., light) output by the LED element  100  as compared to a typically formed (e.g., native) flat or planar surface. The treated surface  112  may provide enhance radiation (e.g., light) extraction efficiency of the LED element  100  due to the scattering of photons from the textured surface  112 . The treated surface  112 , as illustrated in  FIG. 1 , includes micro-roughened texture and macro-roughened texture. 
     The treated surface  112  may be formed using one or more treatments described herein. These treatments are described in further detail with reference to step  304  of the method  300  illustrated in  FIG. 3 . For example, the treated surface  112  may be formed by performing an ion implantation process on a native surface of the GaN layer  110 . The ion implantation process may provide a micro-roughening or texturing of the surface. In an embodiment, the ion implantation process is coupled with additional treatments such as, wet etching, dry etching, KrF laser treatments, and/or other suitable macro-roughening processes. 
     In an embodiment, the treated surface  112  includes an amorphous region of the GaN layer  110 . The amorphous region may be formed by performing an ion implantation process on the GaN layer  110 . The treated surface  112  may include an amorphous regions which extends to an interface with a crystal structure of the GaN layer  110 . The treated surface  112  may be referred to as a boundary layer. In an embodiment, the boundary layer includes the amorphous region having an interface with the crystal structure GaN layer. The boundary layer may include ions such as As, Si, P, BF 2 , Ge, C, B, F, N, Sb, Xe, and/or combinations thereof. The boundary layer (e.g., treated surface  112 ) may include ions that are not present in the underlying GaN layer  110 . The ions included in the boundary layer (e.g., treated surface  112 ) provided by the implantation causing micro-roughing, may not effect the electrical performance of the GaN layer. 
     Referring now to  FIG. 2 , illustrated is an LED element  200 . The LED element  200  also includes a treated surface  202 . The treated surface  202  is roughened (or textured) using one or more treatments such as described below with reference to step  304  of the method  300  illustrated in  FIG. 3 . In an embodiment, the treated surface  202  is formed by performing an ion implantation process on a native surface of a semiconductor layer  204 . The treated surface  202  having greater roughness than a native surface may provide for improved radiation (e.g., light) output by the LED element  200  as compared to an LED element with a planar surface. The treatment or surface texturing techniques provided enhance the radiation (e.g., light) extraction efficiency of the LED element  200  due to the scattering of photons from the treated surface  202 . 
     The treated surface  202 , as illustrated, includes a micro-roughened texture. In other embodiment, the ion implantation process is coupled with additional treatments such as wet etching, dry etching, KrF laser treatments, and/or other suitable macro-roughening processes. These embodiments may provide a micro-roughened and macro-roughened surface. 
     In an embodiment, the treated surface  202  includes an amorphous region of the associated semiconductor layer  204 . In an embodiment, the semiconductor layer  204  is GaN. In a further embodiment, the semiconductor layer  204  is n-GaN. The amorphous region may be formed by the ion implantation of the layer  204 . The treated surface  202  may extend to an interface with a region having crystal structure in the layer  204 . The treated surface  202  may be referred to as a boundary layer. In an embodiment, the boundary layer includes the amorphous region having an interface with the crystal structure GaN layer. The boundary layer may include ions such as As, Si, P, BF 2 , Ge, C, B, F, N, Sb, Xe, and/or combinations thereof. The boundary layer (e.g., treated surface  202 ) may include ions that are not present in the underlying layer  204 . The ions included in the boundary layer (e.g., treated surface  202 ) provided by the implantation causing micro-roughing, may not effect the electrical performance of the layer  204 . 
     The LED element  200  further includes an n-electrode  206 , an active region  208 , a semiconductor layer  210 , a p-electrode conductive layer  212  and a substrate  214 . The substrate  214  further includes a silicon sub-mount  216 , a conductive bonding layer  218  and an electrode  220 . In an embodiment, the semiconductor layer  210  is GaN (e.g., p-GaN). In an embodiment, the active region  208  is InGaN. In an embodiment, the semiconductor layer  204  is GaN (e.g., n-GaN). The LED element  200  is representative only and not intended to be limiting to the LED structure applicable to the present teachings. The LED element  200  may be a completed LED product, or portion thereof, or provided during one or more stages of fabrication. 
     Referring now to  FIG. 3 , illustrated is a method  300  of fabricating an LED element. The method  300  may be used to fabricate the LED element  100 , the LED element  200 , and/or other LED elements.  FIGS. 4-8  are cross-sectional views of an LED element or portion thereof fabricated according to the method  300  of  FIG. 3 . 
     The method  300  begins at step  302  where a plurality of layers forming a vertical structure LED are formed. Referring to the example of  FIG. 4 , a substrate  402  is provided. In an embodiment, the substrate  402  includes sapphire. Other example compositions include silicon, SiC, GaAs, ZnO, GaAs, MgAl 2 O 4 , and/or other suitable materials now known or later developed. The substrate  402  may be referred to as a growth substrate disposed on the LED element during fabrication and subsequently removed. With continuing reference to the example of  FIG. 4 , a plurality of semiconductor layers are disposed on the substrate  402 . In the illustrated embodiment, a first semiconductor layer  404 , an A 1 GaN layer  406 , a multiple quantum well (MQW) element  408 , and a GaN layer  410  are formed on the substrate  402 . In an embodiment, the semiconductor layer  404  includes GaN. The semiconductor layer  404  and/or the A 1 GaN  406  may be a p-type layer (e.g., p-GaN, p-AlGaN). The GaN layer  410  may be an n-type layer or layer having an n-type conductivity (e.g., n-GaN). An exemplary thickness of the semiconductor layer  404  (e.g., GaN), by way of example only and not intending to be limiting, is approximately 50 nm. An exemplary thickness of the A 1 GaN layer  406 , by way of example only and not intending to be limiting, is approximately 20 nm. An exemplary thickness of the GaN layer  410 , again by way of example only, is approximately 2 μm. Numerous other embodiments are possible including various compositions, thicknesses, and LED structures. In an embodiment, various layers are formed on the substrate  402  and a top layer remains a GaN layer (e.g., an n-GaN layer). 
     A top surface  412  of the semiconductor layer  410  is referred to herein as a native surface (e.g., as formed). It is noted that the top surface  412  is substantially planar or flat. In an embodiment, the top surface  412  results from an epitaxial growth of the layer  410 . 
     In an embodiment, the vertical structure LED  400  may be formed using a conductive substrate, such as, for example, SiC for growing semiconductor layer (e.g., GaN layer  404  and  410 ). In an alternative embodiment, the vertical structure LED  400  is formed using a process of providing a growth substrate, and separating and/or removing this substrate (e.g., sapphire) and subsequently bonding a conductive substrate and. For example, in the illustrated embodiment, the layers  404 ,  406 ,  408 , and  410  may be formed on a sapphire substrate  402 . A conductive substrate may be subsequently bonded to one or more of the GaN semiconductor layers. The sapphire substrate  402  may then be removed by laser lift off and/or chemical mechanical polishing processes. In an embodiment, after separating the sapphire substrate  402  one or more electrodes are formed on the LED  400 . Exemplary electrodes include n-type and/or p-type electrodes such as, electrode  114  and/or  206  illustrated above in  FIGS. 1 and 2 , respectively. 
     The treatment process described with reference to block  304  may be performed before and/or after the removal of the growth substrate (e.g., substrate  402 ). In an embodiment, the growth substrate is removed from a GaN semiconductor layer, which is then treated according to one or more aspects of block  304 . In an embodiment, two treatments are performed one on a first conductivity side GaN semiconductor layer prior to removal of the substrate; and one on a second conductivity side GaN semiconductor layer after removal of the substrate. The first and/or second conductivity may be n-type or p-type. 
     Referring now to  FIG. 5 , illustrated is a lattice pattern  502 . The lattice pattern  502  may be the crystal pattern disposed at and near the surface of the semiconductor layer  410  (e.g., the native surface  412 ). The lattice pattern  502  illustrates a crystalline structure. In an embodiment, the lattice pattern  502  is crystalline n-GaN. In an embodiment, the lattice pattern  502  illustrates the crystalline structure of the layer  410  as formed during an epitaxial process. 
     Referring again to  FIG. 3 , the method  300  then proceeds to step  304  where a treatment is performed, which provides for a surface roughening or texturing. The treatment includes a micro-roughening process. In embodiments, the treatment also includes a macro-roughening process. The step  304  may provide a surface substantially similar to as described above with reference to the surface  112  of  FIG. 1  and/or the surface  202  of  FIG. 2 . 
     The treatment of step  304  includes an ion implantation process. The ion implantation provides a micro-roughening (or texturing) of a surface of an exposed layer, such as the layer(s) described above with reference to step  302 . Micro-roughening or texturing of a surface includes surface roughening on a nanometer scale. In other words, the roughening provided includes peak to valley differences on a nanometer scale (e.g., 500 nanometers or less). In contrast, macro-roughening or texturing of a surface, described in further detail below such as provided by a wet etch/clean, includes roughening of a surface an approximately 0.5 μm to approximately 1 μm scale. In other words, the roughening provided includes peak to valley differences of greater than approximately 0.5 μm. 
       FIG. 6  illustrates an ion implantation treatment  602  performed on the lattice pattern  502 , as illustrated in  FIG. 5 . The implantation treatment  602  includes bombarding the lattice pattern  502  (e.g., the surface of an LED element) with one or more ions denoted as  604  and  606 . The ion implantation treatment  602  may modify the lattice pattern  502  or portion thereof (which was previously crystalline) to be amorphous material. The ion implantation treatment  502  may be performed at room temperature or a sub-zero degree Celsius temperature, as described in further detail below. The depth of the treatment  602  (e.g., depth of ion implantation) may be temperature and/or implantation energy dependent. 
     Referring to the example of  FIG. 7 , the surface of the semiconductor layer  410  is treated with the ion implantation process of step  304 . The surface of the treated layer  410  is illustrated as treated surface  702 . The treated surface  702  has an increased roughness as compared to a native surface  412  of the GaN layer  410  (as illustrated in  FIG. 4 ). The increased roughness of the treated surface  702  may be on the micro-scale (e.g., nanometer scale) and thus, referred to herein as micro-roughening. The treated surface  702  includes a peak to valley difference of approximately T. In an embodiment, T is less than approximately 500 nm. In an embodiment, T is between approximately 10 nm and 500 nm. In an embodiment, T is less than approximately 100 nm. The treated surface  702  includes an amorphous layer of material (e.g., boundary layer) formed on the crystalline semiconductor layer of semiconductor layer  410 . 
     The ion implantation process may be performed using a substrate temperature between approximately room temperature (e.g., approximately 25 C.) and approximately −100 C. In an embodiment, the ion implantation process is performed at less than 25 C. In an embodiment, the ion implantation is performed at less than 0 C. The temperature may be based on the substrate temperature and/or a chuck temperature upon which the substrate is disposed for the ion implantation process. Exemplary implant energy is between approximately 1 keV and approximately 3 MeV, by way of example. Exemplary implant dosage is between approximately 1.0E10 and approximately 1.0E16, by way of example. Exemplary implant species (e.g., ions to be implanted) include As, Si, P, BF 2 , Ge, C, B, F, N, Sb, Xe, and combinations thereof. 
     The ion implantation treatment may be performed by implantation equipment such as, for example, high current implanters, medium current implanters, and/or high energy implanters. Example ion implantation systems include those provided by Advance Ion Beam Technology (AIBT) of Fremont, Calif. (including AIBT&#39;s “iPulsar” system); Varian Semiconductor Equipment Associates of Massachusetts (including Varian&#39;s Trident™, 900XP, or 3000XP systems); and Axcelis Technologies of Massachusetts (including Axcelis&#39; HE3 or Optima XE system). 
     In an embodiment of the method  300 , the step  304  includes a macro-roughening treatment prior to the micro-roughening ion implantation treatment described above. In an embodiment, the macro-roughening treatment is a wet etch or wet clean. Exemplary wet etch and clean treatments include KOH solutions. Other exemplary macro-roughening treatments include dry etch processes, laser processes such as the use of KrF laser, nano-imprint lithography, nano-particle-array, pattern sapphire substrate, chemical mechanical polish (CMP) processes, and/or other suitable processes. In embodiments, a plurality of macro-roughening processes may be performed during step  304 . The macro-roughening process(es) may be performed prior to the ion implantation treatment (a micro-roughening process). 
     The treatment of step  304  may be performed on a plurality of layers of an LED element. For example, in the embodiment illustrated in  FIGS. 7 and 8 , a treatment is performed on a n-type GaN layer opposing the substrate  402 . In an embodiment, the substrate  402  is removed and a treatment described in step  304  is performed on the layer  404  (e.g., a treatment is performed on a p-type GaN layer). Various other embodiments are possible and within the scope of the present disclosure. For example, any layer of an LED element, such as a GaN layer (p-type and/or n-type) may benefit from the treatment of step  304 . The treatment may be performed prior to the removal of a growth substrate, after the removal of a growth substrate, prior to the attachment (bonding) of a package substrate (e.g., carrier substrate), and/or after the attachment (bonding) of a package substrate. 
     Referring now to  FIG. 8 , illustrated is an LED  800  that includes a treated surface  802  of the semiconductor layer  410 . The treated surface  802  may also be referred to as a boundary layer. The treated surface  802  illustrates a macro-roughening and micro-roughening affect of treating the semiconductor layer  410 . The macro-roughening affect is illustrated by the wave-like texture to the surface  802 . It is noted that the present illustrations are not to scale but emphasized for ease of understanding. The macro-roughening provides a peak to valley difference of approximately T2 microns. In an embodiment, T2 is between approximately 0.5 μm and 2 μm. The treated surface  802  also includes a micro-roughening including a peak to valley difference of approximately T nanometers. 
     It is noted that the LEDs  700  and/or  800  may be a vertical structure LED elements during the fabrication process and additional process step(s) may occur following the formation of treated surface  702  and  802  respectively. For example, the substrate  402  may be removed, an additional substrate may be attached (bonded) to the element, one or more additional layers may be treated (e.g., layer  404 ) according to one or more aspects of the present disclosure. 
     In an embodiment of the method  300 , the temperature of the ion implantation process may be controlled to provide a desired roughness (e.g., light efficiency) or surface texture. For example, a roughness (relative or absolute) may be determined based on a design goal for the light efficiency of the resultant LED and the temperature of the substrate and/or chuck during the ion implantation process may be selected based on the desired roughness. The desired temperature may be determined from experimental data and/or developed models. The surface roughness dependency on temperature is described below with reference to  FIG. 9 . 
     Referring now to  FIG. 9 , illustrated is a graph  900  which illustrates the intensity of the implantation (y-axis) verses the depth of the implantation affects (x-axis). The intensity of the implantation may be referred to as the damage intensity and may be measured from the concentration of dopants (in dopants/cm 3 ) provided in the bombarded layer (for example, the semiconductor layer  410  described above with reference to  FIG. 4 ). The depth of the implantation affects may be measured in nanometers (e.g., micro-roughening). It is noted that a low-temperature ion implantation  902  provides a greater depth of amorphous material on the surface of a treated layer than that of a room temperature ion implantation  904 . In other words, the lower-temperature ion implantation  902  provides a thicker layer of amorphous material than that of the room temperature ion implantation  904 . Thus, the low temperature ion implantation  902  may provide for a greater surface roughening than the room temperature ion implantation  904 . Therefore, the low temperature ion implantation  902  may provide for a greater radiation output or efficiency than the room temperature ion implantation  904 . 
     In summary, the methods and devices disclosed herein describe LED elements and method of fabrication thereof. In doing so, the present disclosure offers embodiments that provide several advantages over prior art devices. Advantages of embodiments of the present disclosure include an improved roughness of a surface of an LED element, enhanced radiation (e.g., light) output by the element, increased LED efficiency, and/or other advantages. It is understood that different embodiments disclosed herein offer different disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure. For example, the embodiments disclosed herein may be applied to various LED types and structures. 
     Thus, described is an embodiment of a method, which includes providing an LED element including a gallium nitride (GaN) layer disposed on a substrate. The substrate may be a handling or growth substrate, which may be subsequently removed, or a package (e.g., carrier) substrate, which may be disposed in the product LED. The GaN layer is treated. The treatment includes performing an ion implantation process on the GaN layer. In an embodiment, the substrate is at a temperature less than approximately zero degrees Celsius during the ion implantation process. In an embodiment, the ion implantation process is performed at a temperature of less than approximately 25 degrees Celsius. 
     In a further embodiment, the treatment further includes performing a wet etch such an etch using KOH. The ion implantation treatment may provide a micro-roughening of a surface of the GaN layer. 
     An exemplary the ion implantation process includes implanting a species from the group consisting of As, Si, P, BF 2 , Ge, C, B, F, N, Sb, Xe, and combinations thereof. 
     In another embodiment, a method is described that includes providing an LED element including a substrate and a semiconductor layer disposed on the substrate. The semiconductor layer has an exposed top surface. An ion implantation process is performed on the exposed top surface. The ion implantation process is performed while having the substrate at less than approximately zero degrees Celsius. In a further embodiment, the substrate is between approximately zero degrees and −100 degrees Celsius. 
     In embodiments, the method further includes performing a macro-roughening process prior to performing the ion implantation process. Exemplary macro-roughening processes include a wet etch, a dry etch, and a laser treatment (KrF). 
     In an embodiment, the semiconductor layer described above is GaN. In a further embodiment, the semiconductor layer is GaN having an n-type conductivity (n-GaN). 
     Also described is a light emitting diode (LED) element or device. The LED element includes a substrate and a GaN layer formed on the substrate. The GaN layer includes a treated surface having a micro-roughening texture. In an embodiment, the micro-roughening texture includes an amorphous region. In a further embodiment, the treated surface also has a macro-roughening texture. The treated surface may be formed by ion implantation of the GaN layer.