Uniroyal combines the latest quaternary and ternary compounds, with multiple quantum well (MQW) semiconductor technology, to provide the brightest multicandela class LEDs available. For the best in Visible and UV LED results, choose Uniroyal for “The Light Inside”™ your LED-based product. Uniroyal is your one-stop shop for Epitaxial Wafers, Package Ready Die (PRD)™, and custom LED semiconductors.
Quick View: High Brightness LED Wafer Substrates

GaN compound semiconductors, both electro-optical (LEDs,VCELs, etc.) and electronic ICs, are understood to be the next generation of higher performance solid-sate capability. (more)

GaN is the only crystal, the fundamental ingredient of a semiconductor, with bandgap characteristics specifically advantageous for many visible short wavelength and ultraviolet LED applications. (more)

UNIROYAL is unique in its business and technical approach to GaN, and its product implementation work, which includes: high volume production of InGaN/Al2O3 LEDs at UNIROYAL Optoelectronics, and the high volume production of 6H & 4H SiC substrates, SiC Epitaxial products and is conducting work supplying fabricated digital, analog and high-frequency electronic devices at UNIROYAL Sterling Semiconductors. (more)

High Brightness GaN LED Wafer Substrates

GaN compound semiconductors, both electro-optical (LEDs,VCELs, etc.) and electronic ICs, are understood to be the next generation of higher performance solid-sate capability. In electronic applications this means new types of MOSFETs, Memories, Bipolar ICs, Power ICs, RF, Microwave and Milimeterwave devices, to name a few, that will work faster, in harsher conditions, with more bandwidth, more efficiently and with lower power. In the LED industry it means the advent of High Brightness low wavelength devices that will be applied to markets and product applications heretofore totally unattainable, including digitally compatible general “White ”lighting and big screen full-color solid-state outdoor video displays.

GaN is the only crystal, the fundamental ingredient of a semiconductor, with bandgap characteristics specifically advantageous for many visible short wavelength and ultraviolet LED applications. Bulk GaN cannot be grown by itself as a semiconductor crystal in a cost-effective manner yet, mostly because of physical constraints. Indeed, a major difficulty in growing high-quality GaN crystalline films was in establishing a suitable substrate material.

GaN was first successfully produced for High Brightness LEDs via MOCVD epitaxy on Al2O3 (Sapphire) and this combination continues today in large scale production from an increasing supplier base. Subsequently, GaN LEDs have also been produced on SiC (Silicon carbide) substrates as well and are currently in large scale production, albeit with somewhat lower brightness results. Other materials as well, each selected by device designers (both photonic and/or electronic) that base their selection upon the individual materials ’physical properties, are also in development for both LEDs and electronic components. For High Brightness LEDs, the current production platforms are Sapphire and Silicon Carbide, which are compared in the following table:

Parameter
Sapphire
Silicon Carbide
Chemical Formula
Al2O3
SiC
Symmetry
Rhombohedral,C3V
Hexagonal,C6V
C-Axis Lattice Constant,A
12.99
15.117
a-Axis Lattice Constant, A
4.758
3.08
Density, g/mm3
3.98
3.21
Hardness, Mohs
9
9.5
Young Modulus @ 20ºC, Gpa
0.4
488
Tensile Strength @ 20ºC, Gpa
0.12
192
Melting Point, ºC
2050
2850
Specific Heat, cal/g @ 20ºC
0.16
0.16
Heat Capacitance, cal/molºK
16.32
6.4
Thermal Conductivity, W/mºK
41.2
490

Thermal Expansion:

  • Parallel to C–Axis:
  • Perpendicular to C-Axis:
8.5
7.5
4.2
4.68

What goes into the selection of any material for any given semiconductor application are the basic material properties cited above in conjunction with the specific material required for deposition and crystal growth. In addition, other factors not cited above and exhibited by the substrate materials or based upon observation and/or development of various fabrication processes, also play a key part in substrate or superstrate material selection. III-V nitride semiconductors, such as InGaN, exhibit wurtzite (hexagonal lattice) crystal structure with tetrahedral bonding to next neighbors and a direct energy bandgap particularly useful for LEDs in the short wavelength regions. While SiC has a lattice mismatch to GaN of 3.5%, and between Al2O3 the mismatch is 13%, the mismatch, combined with differences in thermal expansion, was resolved by buffer layer deposition processes now used in large scale production. Other undesirable factors too have been reviewed and work-arounds implemented to resolve them, creating very effective results especially in LEDs. Additional observations, that have been part of this High Brightness LED semi-conductor design engineering process, are listed below:

Al2O3

  • Insulating material, requires planar circuitry, needs larger die size and redesigned conventional, traditional package mechanicals for best results.
  • Cost-effective, commonly available, in mass production worldwide
  • Won’t melt until 2050ºC, maintains High Temp Excellent cryogenic conductivity, provides rapid heating and cooling
  • High process survival, scratch resistant, thin material required for equivalent strength, zero porosity, chemically inert
  • Fully transparent media, transmits ultraviolet, visible, infrared and microwaves
  • Low dielectric loss, low dielectric loss: Tan (<104 15% lattice mismatch to GaN and expansion characteristics) accommodated by a buffer layer
  • GaN crystal lattice under compression
  • Poorer heat transfer (4x worse than SiC) somewhat mitigated by use of very thin wafers which are acceptable due to materials good modulus of elasticity the thinner it is.
  • Excellent for superstrate “flip-chip” configuration

SiC

  • Conducting substrate enables backside contactsamenable to use in traditional, conventional packages and minimized die size.
  • Higher cost material with less availability
  • Thermally stable with high thermal conductivity, chemically impervious, mechanically stable.
  • Only wide bandgap (WBG) semiconductor that possess native oxide suitable for MOS insulator in electronic devices (oxidation produces SiO2)
  • The breakdown field in SiC is about 8X higher than in Silicon (important for high-voltage power ICs)
  • With WBG thermal generation of electron-hole pairs is much lower at any temperature (excellent for memories such as DRAMs)
  • GaN crystal lattice under tension
  • Micropipe densities (MPD) range from .5/cm2 to a typical 25 – 50/cm2 , which impact yields and reliability
  • Does not lend itself well to development of “flip-chip” configuration
  • SiC absorbs short wavelength light (greater than or equal to 400 nm)

Others Substrates: Silicon, Diamond, Gallium Nitride, GaAs, ZnO, Spinel (MgAl2O4), Lithium Gallium Oxide and other materials have been used to work with GaN or are in development. Some of this work encompasses LEDs. The potential for homoepitaxy with GaN wafer substrates would virtually eliminate lattice mismatch characteristics, for example, and is under development at many centers throughout the world. ZnO provides only a 2.2% lattice mismatch with GaN and is matched with InGaN. InGaN/ZnO, as well, is being worked with for use in LEDs by yet another cadre of research centers, both public and private.

Each material type posses unique combinations of physical, mechanical, chemical, thermal, electrical, optical, availability and economic characteristics. Frequently it is the combination of three or more of a materials' characteristics that make it the material of choice for a given semiconductor application. Electronic ICs, such as a Power FET, or an optoelectronic device such as a UV Photodetector, have different design criteria, hence different material combinations for each of them may provide the most optimum result. Research and improvements will continue to be pursued with breakthroughs established and used along the way.

UNIROYAL is unique in its business and technical approach to GaN, and its product implementation work, which includes: high volume production of InGaN/Al2O3 LEDs at UNIROYAL Optoelectronics, and the high volume production of 6H &4H SiC substrates, SiC Epitaxial products and is conducting work supplying fabricated digital, analog and high-frequency electronic devices at UNIROYAL Sterling Semiconductors.

 

Interested in semiconductor wafer?

Contact our sister company,
Uniroyal Compound Semiconductor: Sterling Semiconductor, one of the leading and largest supplier of SIC substrates
 
Contact Uniroyal Optoelectronics at (800) 634-8491, or customer.service@uniroyalopto.com
Copyright © 2001 Uniroyal Optoelectronics
webmaster@uniroyalopto.com
This site is optimized for current versions of Internet Explorer or NetScape.