US-12628576-B2 - Fabrication of N-face III-nitrides by remote epitaxy

US12628576B2US 12628576 B2US12628576 B2US 12628576B2US-12628576-B2

Abstract

III-Nitrides epilayer(s) are grown “remotely” on a 2D material layer, such as graphene or h-BN, aBN, or polycrystalline BN coated crystalline substrate, where the Nitride-face surface of the epilayer faces the 2D material. A small mechanical force using a 2D material-based layer transfer process is used to separate the III-Nitrides epilayer(s) at their interface with the 2D material layer. Alternatively, the III-Nitrides epilayer is removed by mechanical force from a substrate with the assistance of a first thermal release tape and an optional metal layer on the epilayer and then a second thermal release tape and/or optional metal layer, is applied to the Nitride-face of the epilayer, the first thermal release tape and first metal layer are removed, the Ga-face surface is bonded to a substrate, and the second thermal release tape is removed. The resulting Nitride-face surface of the epilayer has high quality. A HEMT may be formed using the above structures.

Inventors

Kyusang Lee

Assignees

Kyusang Lee

Dates

Publication Date: 20260512
Application Date: 20221220

Claims (5)

1 . A method of fabricating a III-Nitride epilayer having an exposed Nitride-face, the method comprising the steps of: providing a first substrate; optionally forming a buffer layer on the first substrate if the buffer layer is desired; forming a 2D material interlayer on the buffer layer if the buffer layer is present, or on the first substrate if the buffer layer is not present on the first substrate; using remote epitaxy to grow a III-Nitride epilayer on the 2D material interlayer, the epilayer having a Nitride-face facing the 2D material interlayer and having a metal-face; separating and removing the epilayer from the 2D material interlayer; applying a first thermal release film to the Nitride-face of the epilayer; bonding the metal-face of the epilayer to a second substrate; removing the first thermal release film; applying a second thermal release film on the metal-face of the epilayer; exerting force on the second thermal release film to separate the epilayer from the 2D material interlayer, wherein the step of separating and removing the epilayer from the 2D material interlayer includes the step of exerting force; and removing the second thermal release film alter the step of separating and removing the epilayer from the 2D material interlayer.
2 . A method of fabricating a III-Nitride epilayer having an exposed Nitride-face, the method comprising the steps of: providing a first substrate; optionally forming a buffer layer on the first substrate if the buffer layer is desired; forming a 2D material interlayer on the buffer layer if the buffer layer is present, or on the first substrate if the buffer layer is not present on the first substrate; using remote epitaxy to grow a III-Nitride epilayer on the 2D material interlayer, the epilayer having a Nitride-face facing the 2D material interlayer and having a metal-face; separating and removing the epilayer from the 2D material interlayer; applying a first thermal release film to the Nitride-face of the epilayer; bonding the metal-face of the epilayer to a second substrate; removing the first thermal release film; forming a first stressor layer on the metal face of the epilayer before the step of separating and removing the epilayer from the 2D material interlayer; applying a second thermal release film on the first stressor layer; exerting force on the second thermal release film to separate the epilayer from the 2D material interlayer, wherein the step of separating and removing the epilayer from the 2D material interlayer includes the step of exerting force; removing the second thermal release film after the step of separating and removing the epilayer from the 2D material interlayer; and removing the first stressor layer.
3 . A method of fabricating a III-Nitride epilayer having an exposed Nitride-face, the method comprising the steps of: providing a first substrate; optionally forming a buffer layer on the first substrate if the buffer layer is desired; forming a 2D material interlayer on the buffer layer if the buffer layer is present, or on the first substrate if the buffer layer is not present on the first substrate; using remote epitaxy to grow a III-Nitride epilayer on the 2D material interlayer, the epilayer having a Nitride-face facing the 2D material interlayer and having a metal-face; separating and removing the epilayer from the 2D material interlayer; applying a first thermal release film to the Nitride-face of the epilayer; bonding the metal-face of the epilayer to a second substrate; removing the first thermal release film; forming an adhesion layer on the metal face of the epilayer before the step of separating and removing the epilayer from the 2D material interlayer; forming at least one second stressor layer on the adhesion layer; applying a second thermal release film on the at least one second stressor layer; exerting force on the second thermal release film to separate the epilayer from the 2D material interlayer, wherein the step of separating and removing the epilayer from the 2D material interlayer includes the step of exerting force; removing the second thermal release film after the step of separating and removing the epilayer from the 2D material interlayer; removing the at least one second stressor layer; and removing the adhesion layer.
4 . A method of fabricating a high electron mobility transistor device comprising the steps of: forming a 2D material interlayer on a substrate; forming a high electron mobility transistor device on the 2D material interface, wherein the high electron mobility transistor device comprises a gallium nitride cap layer and a gallium nitride buffer layer having a metal face facing away from the 2D material interlayer and facing the gallium cap layer and a III-Nitride face facing the 2D material interlayer; forming an optional stressor layer on the gallium cap layer; applying a first thermal release film on the optional stressor layer, or on the gallium cap layer in the absence of the optional stressor layer; applying force to the first thermal release film to separate the high electron mobility transistor device from the 2D material interlayer; placing the high electron mobility transistor device on a second thermal release film; removing the first thermal release film; removing the optional stressor layer if it exists; placing the high electron mobility transistor device on a second substrate, wherein the gallium cap layer of the high electron mobility transistor device is adjacent to the second substrate; and removing the second thermal release film.
5 . The method of claim 4 wherein the high electron mobility transistor device comprises: a gallium nitride channel layer on the gallium nitride buffer layer; an aluminum nitride layer on the gallium nitride channel layer; and an aluminum gallium nitride barrier layer between the aluminum nitride layer and the gallium nitride cap layer.

Description

RELATED APPLICATIONS Concurrently filed U.S. patent application titled “Monolithic Remote Epitaxy of Compound Semiconductors and 2D Materials” and having Ser. No. 17/880,692 is incorporated herein by reference in its entirety. FIELD The field of the present disclosure is directed to the fabrication of N-face III-Nitrides. BACKGROUND III-nitride semiconductors have become a cornerstone of modern electronic and optoelectronic devices. The nitrides of group III metal elements include aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), boron nitride (BN) and their alloys, all of which are compounds of nitrogen. III-nitride semiconductors crystallize in their most stable form into a wurtzite crystallographic structure with nitrogen atoms forming a hexagonal close packed (hcp) structure and the group III atoms occupying half of the tetrahedral sites available in the hcp lattice. III-nitrides are polar crystals as they do not have a center of symmetry. III-Nitride semiconductors, when grown on a substrate, can have two different orientations: metal-face and nitride-face (N-face). Metal-face III-Nitrides include, for example, gallium-face (Ga-face), aluminum-face (Al-face), Indium-face (In-face), and Boron-face (B-face) III-Nitrides. The orientation of the final epilayer is a function of the original substrate orientation, buffer growth, and doping conditions. In Ga-face devices, for example, the electron channel forms at the bottom of the AlGaN/GaN (aluminum-gallium nitride/gallium nitride) heterointerface, while in N-face devices, the channel is induced at the top of the GaN/AlGaN interface. N-face III-Nitrides materials may effectively solve problems in various device applications through a polarization inversion. N-face orientation (000ĩ) GaN-based high electron mobility transistors (HEMTs) facilitate very low specific resistance ohmic contacts and form a natural confining electron back barrier over structures grown on the conventional Ga-face. Moreover, for photovoltaic applications, the internal polarization of N-face GaN material would trigger beneficial impacts on the collection of photogenerated carriers. In the MOCVD process, reactant gases are introduced into the system at high pressure, such as about 1 torr. By contrast, the MBE process requires Ultra High Vacuum conditions (i.e., pressures below 10−8 Torr) for deposition. N-face GaN has been obtained generally by nitriding c-plane sapphire (Al2O3) substrate and then applying heavy doping of Magnesium (Mg), and Germanium Ge (111) substrate through the Molecular Beam Epitaxy process. Germanium (111) refers to the (111) crystallographic orientation of the epitaxial Germanium. Also, N-face GaN can be grown on a carbide-face (C-face) (000-1) 6H-SiC substrate with n-type doping of silane (SiH4) by using a low-pressure metal organic chemical vapor deposition (LP-MOCVD) process. 6H-SiC is a silicon carbide composed of two-thirds cubic bonds and one-third hexagonal bonds with a stacking sequences of ABCACB. Remote epitaxy is a technology that grows III-Nitrides epilayers “remotely” on two-dimensional (2D) materials, such as crystalline substrates coated with graphene or monolayer boron nitride (BN), which is also referred to as “white graphene,” without generating significant defects and cracks as long as the potential field from the substrate is strong enough to penetrate through the 2D material interlayers. See, e.g. W. Kong, H. Li, K. Qiao, Y. Kim, K. Lee, Y. Nie, D. Lee, T. Osadchy. R. J. Molnar, D. K. Gaskill, R. L. Myers-Ward, K. M. Daniels, Y. Zhang, S. Sundram, Y. Yu, S.-H. Bae, S. Rajan, Y. Shao-Horn, K. Cho, A. Ougazzaden, J. C. Grossman, and J. Kim, “Polarity governs atomic interaction through two-dimensional materials,” Nature Materials, vol. 17, pp. 999-1004, 2018. The interface between III-Nitrides epilayers and 2D materials can be separated by applying a minimal or small mechanical force by using a 2D material based layer transfer (2DLT) process because 2D materials have a weak vertical van der Waals interaction that can be easily overcome. See, e.g., Y. Kim, S. S. Cruz, K. Lee, B. O. Alawode, C. Choi, Y. Song, J. M. Johnson, C. Heidelberger, W. Kong, S. Choi, K. Qiao, I. Almansouri, E. A. Fitzgerald, J. Kong, A. M. Kolpak, J. Hwang, and J. Kim, “Remote epitaxy through graphene enables two-dimensional material-based layer transfer,” Nature, vol. 544, pp. 340-343, 2017, the entirety of which is incorporated herein by reference. However. N-face GaN epilayers have received less attention due to difficulties in achieving high-quality growth and smooth surface roughness compared to Ga-face GaN. Thus, there is a need for an improved method of fabricating N-face III-Nitrides with high quality growths and smooth surfaces. SUMMARY The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the improved method. This summary is not an extensive overview of the invention, is not intended to