Kubos Cubic Technology Vs Hexagonal GaN Technology


Kubos’s LED TechnologyConventional LED Technology
Quantum Confined Stark-Effect (QCSE) impact on device performance
Electric-field free LEDs : Cubic GaN does not have built in electric-field across the QWs and therefore does not suffer from the QCSE.The QCSE, due to the built in electric-fields in hexagonal GaN, is believed to be one of the key factors that limits the efficiency of LEDs at green and amber wavelengths.
Bandgap Engineering
Significantly lower indium content is required in cubic InGaN QWs to deliver LEDs emitting at green and amber wavelengths.

Removal of the QCSE allows wide QWs (>3nm) with large Electron-Hole wavefunction overlap. This reduces carrier density in the QWs and gives another degree of freedom for the design of efficient green and amber LEDs.
The high Indium content required to extend emission wavelengths in to the green and amber, gives rise to an increased QCSE. Also growth of high quality, high Indium content QWs is challenging.

Due to the QCSE, this technology is limited to relatively thin QWs (<3nm). This increases carrier density and gives a spectral shift as the drive current density is increased.
Electron-Hole wavefunction overlap (Γe-hh)
Removal of the QCSE improves the Electron-Hole wavefunction overlap in the QWs, increasing radiative recombination and reducing carrier lifetime.Increased QCSE for high indium content QWs reduces the Electron-Hole wavefunction overlap, reducing radiative recombination and increasing carrier lifetime.
Carrier Lifetime
Short carrier lifetimes contributes to efficient radiative recombination of electrons and holes. This also means that cubic-GaN LEDs may be ideal for applications requiring fast switching such as “LiFi”.Long carrier lifetime in the active region increases probability of non-radiative recombination processes.
Improved spectral stability
Absence of the QCSE means that there is no screening of electric fields as carrier density is increased. This gives improved stability of the emission wavelength.The large QCSE means that as the drive current is increased the internal electric fields are screened by the carriers. This causes a shift in the emission wavelength.
Substrate Size & Type
Growth of cubic GaN has been demonstrated upto 150mm and is scalable to 200mm and 300mm using CMOS compatible (001) Si wafers.Currently available upto 150mm on sapphire and 200mm on (111) Si.
Efficiency Droop
Overcoming the efficiency droop: Due to reduced carrier density and differences in band structure it is predicted that cubic GaN based LEDs may show reduced efficiency droop. This is currently being investigated.Efficiency droop is a major challenge for conventional GaN based LEDs in high drive current applications.