LED_grid_new_edited.jpg

Passivation of sidewalls for III-V MESA structures

Many optoelectronic devices consist of multilayer stacks of different compound semiconductor materials processed to form so-called mesa structures which are essentially 3D structures on a semiconductor wafer. When the sidewalls and surfaces of these structures are exposed to oxygen, the formation of native oxides starts,  promoting the formation of a high density of defects.

In optoelectronic devices, these defects act as non-radiative recombination centers, meaning that whenever the charge carrier, for instance, electron injected to led, encounters this kind of defect, it will be recombined in a way that no photon is emitted but the energy of the charge carrier is wasted as heat. Furthermore, such defects are the pathways for considerable leakage currents and will have significant contributions for instance in photodetector performance (sensitivity, stn ratio, dark-current).

As the size of optoelectronic devices becomes smaller, the impact of surface recombination will start to play a very significant role. In many compound semiconductor materials, a so-called diffusion length of charge carriers can be very large, meaning that the carriers are able to propagate in the material substantial distances before recombining either radiatively or non-radiatively. This also means that when the device or the chip size is comparable or even less than the diffusion length, the carriers are easily lost in the defects at the defective sidewalls of the chips.

This surface recombination and leakage of carriers impose serious limitations on the efficiency of nanocavity light-emitting diodes, vertical cavity surface-emitting lasers with oxidized apertures, and other devices such as photodetectors concentrated photovoltaic solar cells and nanowire devices where the size of the active region is comparable to the minority carrier diffusion length.

S1_Im_15um_5mm_T2_26.tif
oxidezed interace close-up.png

SEM image of a microLED (left) and high-resolution TEM image of a microLED sidewall showing defective oxidized surface (right)

Application case: microLED

The display industry is coming to a major turning-point due to high demand and unprecedented requirements of power efficiency and brightness driven by next-generation information displays, automotive, VR/AR, and IoT applications.  MicroLED technology is currently the only way for that transformation.

 

There are numerous obstacles in realizing a good quality, high yield, mass-production-ready micro-LED display. Poor efficiency at low current densities and variation of emission level between chips is one of the key issues that is directly related to the quality of the sidewalls of the chips and the high surface recombination effects. These effects become more prominent as the chip size gets smaller.

Kontrox forms a high-quality passivation layer with substantially reduced defect densities which improves the microLED device power efficiency and brightness levels significantly. 

Substrate wafers

Kontrox forms a high-quality homogeneous termination layer to reduce epi-growth defects and improve wafer bonding processes. 

Compound semiconductor transistors

Kontrox drastically reduces the surface defect state density at the interface between the semiconductor and the gate dielectric.