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EP-4238123-B1 - METHOD OF TRANSFERRING A PATTERN TO AN EPITAXIAL LAYER OF A LIGHT EMITTING DEVICE

EP4238123B1EP 4238123 B1EP4238123 B1EP 4238123B1EP-4238123-B1

Inventors

  • GANDROTHULA, Srinivas
  • KAMIKAWA, TAKESHI

Dates

Publication Date
20260506
Application Date
20211028

Claims (15)

  1. A method of providing one or more light-emitting devices, comprising: preparing a host substrate; depositing a growth restrict mask on the host substrate, wherein one or more patterns are formed in the growth restrict mask on the host substrate, and the growth restrict mask includes opening areas that expose the host substrate; growing one or more epitaxial lateral overgrowth, ELO, layers on the host substrate from the opening areas in the growth restrict mask, and then laterally over the growth restrict mask and the patterns formed in the growth restrict mask, wherein patterns comprise one or more random valley-hill patterns that are transferred onto the ELO layers, resulting in light controlling structures in the ELO layers; and forming one or more device layers that emit light on the ELO layers.
  2. The method of claim 1, wherein the patterns are formed on the host substrate.
  3. The method of claim 2, wherein the one or more patterns are transferred onto the growth restrict mask.
  4. The method of claim 1, wherein the device layers include copies of the patterns.
  5. The method of claim 1, wherein the patterns result in light controlling structures at an interface between the ELO layers and the growth restrict mask.
  6. The method of claim 1, wherein the patterns comprise one or more unleveled regions.
  7. The method of claim 1, wherein the host substrate has trenches.
  8. The method of claim 1, wherein the method is independent of crystal orientations of the host substrate.
  9. The method of claim 1, wherein the growth restrict mask is comprised of one or more layers.
  10. A light-emitting device, comprising: a host substrate; a growth restrict mask on the host substrate, wherein one or more patterns are formed in the growth restrict mask on the host substrate, and the growth restrict mask includes opening areas that expose the host substrate; one or more epitaxial layers on the host substrate in the opening areas in the growth restrict mask, and extending laterally over the growth restrict mask and the patterns formed in the growth restrict mask, wherein the patterns comprise one or more random valley-hill patterns that are transferred onto the laterally extending epitaxial layers, resulting in light controlling structures in the laterally extending epitaxial layers; and one or more device layers that emit light formed on the laterally extending epitaxial layers
  11. The device of claim 10, wherein the device is a light emitting diode or a vertical cavity surface emitting laser.
  12. The device of claim 10, wherein the patterns are formed on the host substrate and transferred onto the growth restrict mask.
  13. The device of claim 10, wherein device layers include copies of the patterns.
  14. The device of claim 10, wherein the patterns result in light controlling structures at an interface between the lateral extending epitaxial layers and the growth restrict mask.
  15. The device of claim 10, wherein the patterns comprise one or more unleveled regions.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention. This invention relates to a method of transferring a pattern to an epitaxial layer of a light emitting device. 2. Description of the Related Art. For III-nitride semiconductor devices, such as light emitting diodes (LEDs) and laser diodes (LDs), both extraction and the corresponding output power have been greatly improved by surface roughening methods such as patterned sapphire substrate (PSS) and photoelectrochemical (PEC) etching techniques. In the case of III-nitride LEDs, light extraction efficiency has become the most important limiting factor for the efficiency of the LEDs, since the internal quantum efficiency (IQE) of nitride-based LEDs has been greatly improved (more than 80%) by the availability of low-dislocation GaN substrates and advances in metal organic chemical vapor deposition (MOCVD) techniques. The effectiveness of these surface roughening methods by and large depends on the crystal orientation and polarity of the to-be-patterned surface. So far, it has only been established for the nitrogen-face of a c-polar [0001] GaN and has not yet been available for arbitrary GaN crystal orientations and polarity, including most semipolar surfaces and nonpolar a-plane and m-plane surfaces. Reactive ion etching (RIE) is another method used to pattern conical features to enhance light extraction irrespective of crystal orientation. On the other hand, a limitation lies in the non-controllability of the direction of emitted light. Improving the directionality of light emission has been widely studied either through the use of microcavities or photonic crystals (PhCs) to control the propagation of electromagnetic modes in optoelectronic devices. The periodic modulation of refraction serves as an optical grating to couple guided modes from the semiconductor device to air, thus increasing extraction efficiency and directionality of LEDs. The application of gratings for the light diffraction in optoelectronic devices requires the grating period to be on the order of half of the wavelengths of the light generated by the device. In the case of GaN based optoelectronic devices, the grating period needs to be on the order of a few hundreds of nanometers. The main difficulty of PhC LEDs is their delicate required fabrication. Thus, there is a need in the art for improved methods of fabricating light guiding or extracting features. SUMMARY OF THE INVENTION To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding this specification, the present invention discloses a method according to claim 1 wherein one or more light-emitting devices fabricated on a wing of III-nitride epitaxial lateral overgrowth (ELO) layers, thereby resulting in a device that has good crystal quality in terms of reduced dislocation densities and stacking faults. Specifically, this invention performs the following steps: island-like III-nitride semiconductor layers are grown on a substrate using a growth restrict mask and the ELO method, where the growth restrict mask plays an important role for obtaining a desired light extraction or light guiding function. Before the growth, the growth restrict mask is patterned with one or more random valley-hill patterns. Thereafter, devices are fabricated on the wings of the III-nitride ELO layers, and the devices are plucked from the host substrate. Note that isolated devices may remain on the host substrate with a very minimal link, such as an epitaxial or non-epitaxial bridge, until the whole device is finished. Once removed from the substrate, the devices may be transferred to another carrier or substrate by an elastomer stamp, vacuum chuck, adhesive tape, or simply by bonding or attaching the devices to the separate carrier or substrate. The III-nitride semiconductor layers are dimensioned such that one or more of the island-like III-nitride semiconductor layers form a bar (known as a bar of a device). By doing this, nearly identical devices can be fabricated adjacent to each other in a self-assembled array, and thus, by integration, scale up can be made easier. Alternatively, the III-nitride ELO layers can be made to coalesce initially, such that they can be later divided into bars of devices or individual devices. Every device can be addressed separately or together with other devices, by designing a proper fabrication process. For example, one could make a common cathode or anode for such a bar of devices for monolithic integration, or one can address individual devices for full color display applications. Consequently, a high yield can be obtained. Key aspects of this invention include: Light extraction and/or directionality are controlled.Light extraction or guiding features are introduced on wings of the III-nitride ELO layers, before growth of active layers of the device.Light extraction or guiding features are placed on a backside of the III-nit