4-inch (20-21) GaN on Sapphire Template
A Solution to Green Gap and Efficiency Droop Problems
First-generation GaN materials are subject to large built-in electric fields due to spontaneous and piezoelectric polarization. Devices can only operate at low current densities due to the rapid decrease of efficiency (efficiency droop) as the current density increases. As a result, total brightness per given chip area is low, hindering LED and laser usage in many high power applications. In addition, long wavelength devices are still absent due to significantly low performance between 520 and 635 nm (green gap), limiting display and illumination applications for the highest spectral sensitivity of the human visual perception of brightness.
Semi-polar gallium nitride (GaN) materials can address these long-standing problems with lower polarization-induced electric fields and reduced blue shift. The reduction of efficiency droop can be achieved by increasing the volume of the InGaN active region. Quantum Confined Stark effect (QCSE) is eliminated by reducing polarization fields. Semi-polar materials have also been used to enable high efficiency long wavelength devices such as direct green lasers.
Traditionally, semi-polar materials are produced by the off-axis slicing of bulk form HVPE-grown GaN substrates that are expensive and physically incompatible with mass production. To overcome this obstacle, Saphlux uses an innovative orientation controlled epitaxy (OCE) method to selectively grow semi-polar GaN materials directly on standard sapphire wafers. The C-plane GaN is grown obliquely from the sidewall of trench-etched substrates to produce stacking-fault free semi-polar GaN upon coalescence that can be mass-manufactured.
With the recent success of Saphlux in mass-producing such materials, the “end of Moore’s Law” could be in sight for conventional c-plane GaN device.
Semi-polar Laser Diode
High-power and High-efficiency True Green Laser Diodes
Ultraviolet Laser Diodes Grown on Semi-polar (20-21) GaN Substrates by Plasma-assisted Molecular Beam Epitaxy
Applied Physics Letters, 102 251101 (2013)
High-Power (over 100mW) Green Laser Diodes on Semi-polar (20-21) GaN Substrates Operating at Wavelengths beyond 530nm
Applied Physics Express, 5 (2012) 082102
Optical Polarization Characteristics of InGaN Quantum Wells for Green Laser Diodes on Semi-Polar (20-21) GaN Substrates
Applied Physics Express, 3 (2010) 011003
531nm Green Lasing of InGaN Based Laser Diodes on Semi-Polar (20-21) Free-Standing GaN Substrates
Applied Physics Express, 2 (2009) 082101
Ongoing LED R&D Challenges (LED droop still challenge)
Complete Orientational Access for Semipolar GaN Devices on Sapphire
Semi-polar (20-21) GaN and InGaN quantum wells on sapphire substrates
Semi-polar (20-2-1) InGaN/GaN Light-Emitting Diodes
for High-Efficiency Solid-State Lighting
Journal of Display Technology, VOL. 9, NO. 4, APRIL 2013
High-Efficiency Single-Quantum-Well Green and Yellow-Green Light-Emitting Diodes on Semipolar (20-21) GaN Substrates
Applied Physics Express, 3 (2010) 122102