Device and method for III-V light emitting micropixel array device having hydrogen diffusion barrier layer
11495714 · 2022-11-08
- Hussein El-Ghoroury (Carlsbad, CA, US)
- Kameshwar Yadavalli (Fremont, CA, US)
- Andrew Teren (Carlsbad, CA, US)
- Qian Fan (Carlsbad, CA, US)
- H01L2933/0025 20130101
- H01L33/62 20130101
- H01L27/156 20130101
- H01L33/44 20130101
- H01L33/06 20130101
- H01L33/12 20130101
- H01L33/0093 20200501
- H01L25/167 20130101
- C23C18/2066 20130101
- H01L33/32 20130101
- H01L33/382 20130101
- C23C18/20 20060101
- H01L33/12 20100101
- H01L33/38 20100101
- H01L33/32 20100101
- H01L27/15 20060101
- H01L33/06 20100101
- H01L33/00 20100101
- H01L33/44 20100101
Solid state light emitting micropixels array structures having hydrogen barrier layers to minimize or eliminate undesirable passivation of doped GaN structures due to hydrogen diffusion.
1. A multi-layer semiconductor light emitting structure comprising: a first region having a first composition; a second region having a second composition; at least one multiple quantum well active region between the first and second regions; at least one hydrogen barrier layer on the first region; a sidewall pixel contact cap that extends into the first region; and; a plurality of contact vias that electrically couple the sidewall pixel contact cap to a contact metal rail; wherein the first region is completely enveloped or encapsulated by either (i) the at least one hydrogen barrier layer, or (ii) by the sidewall pixel contact cap and the contact vias, thereby preventing or minimizing a hydrogen penetration into the first region of the multi-layer semiconductor light emitting structure.
2. The multi-layer semiconductor light emitting structure of claim 1, wherein the at least one hydrogen barrier layer is an undoped GaN capping barrier layer.
3. The multi-layer semiconductor light emitting structure of claim 1, wherein the at least one hydrogen barrier layer is of III-nitride material.
4. The multi-layer semiconductor light emitting structure of claim 1, further comprising: a metal ring wrapped around corners of the topside of the multi-layer semiconductor light emitting structure to create a base for the contact vias; whereby the topside of the multi-layer semiconductor light emitting structure comprises an optically transparent aperture area unobstructed by the contact vias in order to achieve maximum light output while achieving a large contact area along a sidewall of the first region.
5. The multi-layer semiconductor light emitting structure of claim 1, wherein doping of the first region is graduated, either continuously or stepped, from an undoped GaN portion adjacent to the at least one multiple quantum well active region to p.sup.+-GaN, to p.sup.++-GaN, to p.sup.+-GaN, to p-GaN, and to an undoped GaN portion on the topside of the first region; whereby the graduated doping of the first region effectively blocks hydrogen diffusion into the first region.
6. The multi-layer semiconductor light emitting structure of claim 1, wherein the sidewall pixel contact cap comprises at least two metal layers and a thickness selected to achieve an ohmic contact between the sidewall pixel contact cap and the first region.
7. The multi-layer semiconductor light emitting structure of claim 1, wherein thickness of the at least one hydrogen barrier layer is about 10 nanometer (nm) to about 50 nm.
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The embodiments herein are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate like or similar elements.
(2) The matters defined in the description, such as detailed construction and elements, are provided to assist in an understanding of the exemplary embodiments. However, the present invention can be practiced without those specifically-defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the invention with unnecessary detail. In order to understand the invention and to see how it may be carried out in practice, a few embodiments are described by way of non-limiting example only with reference to the accompanying drawings, in which:
(9) References in the following detailed description of the present invention to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in this detailed description are not necessarily all referring to the same embodiment.
(10) P-type doping in GaN material is most commonly achieved using Mg dopant atoms which are considered among the most effective dopants (see J. K. Sheu & G. C. Chi, “The doping process and dopant characteristics of GaN”, J. Phys.: Condens. Matter 14 (2002) R657-R702). Typically, Mg dopants in MOCVD-grown GaN-based LED devices and structures are passivated by hydrogen during the epitaxial growth process. The MOCVD-grown structures then later require a post-growth high temperature anneal to activate the Mg dopants for effective device operation.
(11) Detrimental hydrogen exposure by the GaN material of the diode structure can occur at multiple steps during the fabrication of a multilayer light emitting semiconductor device such as, for example, a micropixel array emissive device. The hydrogen incorporated during the growth/post-growth phase in the reactor itself is a major source of hydrogen exposure, but an additional source of hydrogen exposure is the hydrogen to which GaN-based materials or devices are exposed during subsequent device fabrication steps. For instance, a common semiconductor process step resulting in significant device hydrogen exposure is a well-known process known as “plasma enhanced chemical vapor deposition” (“PECVD”) of dielectrics used in semiconductor manufacturing. Various other common semiconductor process steps also lead to hydrogen incorporation in III-V nitrides in general (see S. J. Pearton, R. J. Shul, R. G. Wilson, F. Ren, J. M. Zavada, C. R. Abernathy, C. B. Vartuli, J. W. Lee, J. R. Mileham & J. D. Mackenzie, “The incorporation of hydrogen into III-V nitrides during processing”, J. Electron. Mater., 25, 845 (1996)).
(12) The fabrication of GaN-based micropixel array emissive devices such as the QPI display device or other microLED devices often requires the deposition of dielectric layers such a silicon oxide (“SiO.sub.2”) passivation layer on the etched pixel sidewall or as an electrical isolation layer within the light emissive diode structure. Silicon oxide may also be used as an intermediary bonding layer in a multilayer semiconductor device comprising a plurality of semiconducting light emitting layers.
(13) During the deposition of such silicon oxide layers, which is typically performed using plasma enhanced chemical vapor deposition (PECVD), the undesirable inclusion of excess hydrogen and/or hydroxyl (OH) groups is inevitable. At typical deposition temperatures of subsequently deposited silicon oxide layers, hydrogen that has become disassociated from previously deposited silicon oxide layers diffuses and causes undesirable passivation of the GaN doping, particularly p-type doping, within the diode structure. This in turn results in a reduction in GaN-based micropixel diode efficiency. This is even more problematic with silicon oxide layers that are in close proximity to the GaN layer of the light emissive micropixel diode structure.
(14) In the typical fabrication of solid state light emitting diode material structures, hydrogen is used as a carrier gas for the epitaxial growth of the GaN material using, for instance, metal organic chemical vapor deposition (MOCVD). Since the hydrogen carrier gas flow remains in the chamber throughout the epitaxial growth process of the GaN-based material, there is often a high concentration of hydrogen in the layers of the GaN structure. When this GaN-based material is used in the fabrication of GaN-based solid state light emitting diode structures, the associated elevated processing temperatures of subsequent processing steps leads to diffusion of MOCVD residual hydrogen into the doped region of the diode structure material and detrimentally causes passivation of the dopants in the GaN material itself. This in turn, reduces the efficiency (IQE) of the GaN material comprising the diode structure and is particularly harmful to the p-doped region of the structure.
(15) To address these concerns and other deficiencies in the prior art relating to GaN-based light emitting structures, in one aspect of the invention, a multilayer GaN-based III-Nitride light emitting micropixel array device is disclosed comprising one or a plurality of stacked light emitting layers wherein at least one of the light emitting layers comprises a hydrogen barrier layer.
(16) The disclosure below describes a non-limiting embodiment of a method and structure of the invention that eliminates or significantly minimizes the detrimental effects of hydrogen diffusion during the fabrication process of GaN-based solid state light emitting diode structures and devices. The method includes the selected growth of one or a plurality of hydrogen barrier layers during the epitaxial growth of the GaN material and/or deposition of additional hydrogen barrier layers during the fabrication process of the GaN-based solid state light emitting diode structures.
(18) In one embodiment, the hydrogen barrier layer 1000 may be a final layer that is deposited during the epitaxial growth of the light emitting structure 1. With this method, excess hydrogen carrier gas is isolated from the GaN-based diode structure by the deposited barrier layer 1000 which is designed to reduce the diffusion of excess hydrogen into the GaN-based diode structure. In an alternate embodiment, the barrier layer 1001 may be deposited during the fabrication process of the array of micropixel mesas. In another embodiment, both the epitaxially grown hydrogen barrier layers 1000 and the process-deposited barrier layer 1001 are used to realize further advantages as explained in the forthcoming description of the fabrication methods of these embodiments.
(19) In the embodiment in which the barrier layer 1000 is epitaxially grown, the selected material of hydrogen barrier layer 1000 is preferably a material that is epitaxially compatible with the GaN material of the diode structure and preferably exhibits a band gap and crystalline properties that prevent or minimize the diffusion of hydrogen into the diode structure 1. A suitable hydrogen barrier 1000 material may comprise undoped GaN or aluminum nitride (AlN) or an alloy of these two materials. AIN is a member of the III-Nitride material group with GaN and as such is epitaxially compatible with the GaN material of the diode structure. Aluminum nitride has a wider band gap energy (6.2 eV) than GaN (3.4 eV). In general, the highly crystalline aspects of the epitaxially grown layer 1000, whether of GaN, AlN or an alloy of the two materials, serves to enhance their hydrogen diffusion properties.
(20) A further suitable material for hydrogen barrier layer 1000 is an aluminum gallium nitride (Al.sub.xGa.sub.1-xN) material having a ratio of aluminum (.sub.x) being selected to ensure the requisite barrier layer 1000 band gap energy necessary to form an effective barrier to block diffusion of hydrogen to the underlying GaN material.
(21) An advantage of using (Al.sub.xGa.sub.1-xN) material for hydrogen barrier 1000 is to assist in balancing the lattice strain between the GaN diode layers and barrier layer 1000 through the appropriate selection of the aluminum (.sub.x) ratio within the AlGaN material composition of barrier layer 1000. A further advantage of using AlGaN as barrier layer 1000 is to facilitate the ease of subsequent selective etching of barrier layer 1000 to deposit p-type and n-type contacts, or to access previously deposited p-type and n-type contacts on the underlying GaN material, again through the appropriate selection of the aluminum (.sub.x) ratio within the AlGaN material composition of barrier layer 1000.
(22) In the embodiment in which the barrier layer 1001 is process-deposited, the selected material of hydrogen barrier layer 1001 is a material that preferably exhibits properties that prevent or minimize the diffusion of hydrogen into the diode structure 1. In this embodiment, the hydrogen barrier layer 1001 may be an aluminum oxide (Al.sub.2O.sub.3) that may be deposited using sputtering (physical vapor deposition), PECVD or atomic layer deposition (ALD) techniques. The wider band gap energy of an Al.sub.2O.sub.3-based barrier layer (1001) effectively acts to block hydrogen diffusion through to the GaN diode structure. Another suitable material for the deposited hydrogen barrier layer 1001 is magnesium oxide (MgO). Magnesium oxide surface layers are known to retard hydrogen diffusion (see T. R. Jensen, A. Andreasen, T. Vegge, J. W. Andreasen, K. Stahl, A. S. Pedersen, M. M. Nielsen, A. M. Molenbroek & F. Besenbacher, “Dehydrgenation kinetics of pure and Ni-doped magnesium hydride investigated by in situ time-resolved powder X-ray diffraction”, Int. J. Hydrog. Energy 31 (14), 2052-2062 (2006)). Another factor enabling the hydrogen barrier property of oxides is the strong bond between oxygen and hydrogen which is known to increase activation enthalpy for proton diffusion in oxides (see W. Munch, G. Seifert, K. Kreuer & J. Maier, Solid State Ionics, 88, 647-652 (1996)). Also, formation of molecular orbitals is shown to lead to blocking of slow hydrogen projectiles in large band-gap dielectric oxides (see K. Eder, D. Semrad, P. Bauer, R. Golser, P. Maier-Komor, F. Aumayr, M. Penalba, A. Arrau, J. M. Ugalde, & P. M. Echenique, “Absence of a “Threshold Effect” in the Energy Loss of Slow Protons Traversing Large-Band-Gap Insulators”, Phys. Rev. Lett. 79 (21), 4112-4115, 1997).
(23) Barrier layer 1000/1001 is preferably of a thickness of about 10 nm to about 50 nm to facilitate subsequent etching through barrier layer 1000/1001 for subsequent deposition of, or electrical access to, p-type or n-type contacts on the GaN surface. Barrier layer 1000/1001 may be up to 100 nm thick.
(24) In the method and device illustrated in
(25) It is expressly noted the illustrated fabrication methods and structures of the invention are not limited to the fabrication of devices comprising micropixel mesa structures 1060 and that the disclosed method and structure can be beneficially applied to any light emitting semiconductor structure where there is a risk of hydrogen diffusion passivating doping in its GaN-based diode structure, such as in a microLED or other solid state light emitting structure.
(26) The micropixel separation sidewall 1070 spacing width in an embodiment of the micropixel mesa structure array of
(27) In order to electrically isolate micropixel diode mesas 1060 from the sidewall filling material, which may be a metal such as nickel, the micropixel sidewalls GaN surface is preferably first passivated with an industry-standard semiconductor dielectric material such as silicon oxide or silicon nitride. The hydrogen barrier layer 1001 material which may be deposited prior to deposition of passivation layer above also beneficially serves as a passivation layer for micropixel sidewalls 1070 in addition to providing a hydrogen diffusion barrier 1000. The added advantage of this method is that a hydrogen barrier 1001 function is provided on both the top side as well as the sidewalls 1070 of micropixel mesas 1060, thus avoiding diffusion of hydrogen to the GaN material potentially from sidewall passivation layers like silicon oxide or silicon nitride. In
(28) In the described method, a barrier layer 1001 of high dielectric constant material is deposited, as illustrated in
(29) The deposited barrier layer 1001, having a thickness ranging from about 10 nm to about 50 nm, may be etched on the top side of the micropixel mesas 1060 in order to deposit or access micropixel metal contact vias that are used to connect to metal contacts that are selectively deposited on the top side of the micropixel mesas 1060 prior to the deposition of hydrogen barrier layer 1001. The micropixel's metal contacts are designed to provide an unobstructed micropixel aperture area for the emitted light to emerge from the micropixel mesas 1060.
(30) In one embodiment of the micropixel array hydrogen barrier device illustrated in
(32) Following the deposition of backside barrier layer 1001, the deposited barrier layer 1001 is etched, using wet or dry etching methods, to expose the metal contacts of the micropixel mesas' backsides that have been deposited prior to the deposition of back side barrier layer 1001. After the micropixel mesa backside metal contacts are exposed, metal vias may be deposited to make the micropixel mesa contacts electrically accessible on the surface of backside barrier layer 1001.
(33) Referring to
(36) Referring to
(38) An array of the barrier layer 1000 encapsulated micropixels of
(39) Referring to the barrier layer 1000 encapsulated micropixels of
(41) As illustrated in
(42) As is illustrated in
(43) As illustrated in
(44) The graduated doping of the p-GaN region together with the sidewall p-contact metal cap ensures efficient p-contact to the pixel p-GaN region while ensuring an effective barrier for blocking hydrogen diffusion into the pixel p-GaN region.
(45) As illustrated in
(46) The p-contact of the micropixel cap is deposited on the p-GaN region of the pixel sidewall using standard semiconductor thin film deposition methods such as e-beam deposition or sputtering. The p-contact pixel cap is deposited on the p-GaN region of the pixel sidewall and may be comprised of at least two thin metal layers such as Ni, Au, Pt, or Pd (but not limited to these) with a thickness and function selected to achieve an ohmic contact between the p-contact cap and the p-GaN region of the pixel.
(47) In a non-limiting example of a method for manufacturing the above structure, a GaN wafer is pixelated by etching the pixel sidewalls using standard III-V semiconductor processing methods and plasma-based dry etching in combination with appropriate wet etching to achieve the required pixel sidewall angle and surface smoothness. The etched sidewalls are passivated by means of the deposition of a thin dielectric layer of for instance, silicon oxide or silicon nitride, or a combination of both. The passivation layer is etched off the p-GaN region of the pixel sidewall and the ohmic p-contact cap metal layer deposited on the sidewall region. After deposition of the p-contact cap, the pixel sidewall is passivated again using a thin layer of silicon oxide, silicon nitride or both. After the pixel sidewall is passivated a second time, the remaining trenches of the sidewalls are filled with a metal such as tin or nickel (but not limited to these) which act to optically isolate the pixels and used as vias to interconnect the pixels with appropriate control signals.
(48) Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by any claims in any subsequent application claiming priority to this application.
(49) For example, notwithstanding the fact that the elements of such a claim may be set forth in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different elements, which are disclosed in above even when not initially claimed in such combinations.
(50) The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus, if an element can be understood in the context of this specification as including more than one meaning, then its use in a subsequent claim must be understood as being generic to all possible meanings supported by the specification and by the word itself.
(51) The definitions of the words or elements of any claims in any subsequent application claiming priority to this application should be, therefore, defined to include not only the combination of elements which are literally set forth, but all equivalent structure, material or acts for performing substantially the same function in substantially the same way to obtain substantially the same result. In this sense, it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements in such claims below or that a single element may be substituted for two or more elements in such a claim.
(52) Although elements may be described above as acting in certain combinations and even subsequently claimed as such, it is to be expressly understood that one or more elements from a claimed combination can in some cases be excised from the combination and that such claimed combination may be directed to a subcombination or variation of a subcombination.
(53) Insubstantial changes from any subsequently claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of such claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements.
(54) Any claims in any subsequent application claiming priority to this application are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention.