GaN-based light emitting diodes (LEDs) and high electron mobility transistors (HEMTs) grown on silicon substrates have the potential of low cost manufacturing for solid state lighting and power electronics. To fully explore the ultimate performance of the devices, a transfer process was developed to place the devices onto a potentially more suitable substrate for comparison of performance....[ Read more ]

GaN-based light emitting diodes (LEDs) and high electron mobility transistors (HEMTs) grown on silicon substrates have the potential of low cost manufacturing for solid state lighting and power electronics. To fully explore the ultimate performance of the devices, a transfer process was developed to place the devices onto a potentially more suitable substrate for comparison of performance.

In this research work, GaN-based LEDs and HEMTs grown on silicon substrates were transferred onto different substrates by a double-flip transfer process. Fabricated devices on the silicon substrate were bonded to a temporary substrate in the first flip. After the silicon removal by chemical etching, the devices were transferred to a new substrate as the second flip.

LEDs on silicon were transferred to electroplated copper substrates with a reflective mirror inserted. The optical output power of LEDs on copper increased up to 114%, as compared to those on the original silicon substrate before transfer. The significant improvement was attributed to the replacement of the light-absorbing silicon substrate with a mirror layer and better heat dissipation through the new copper substrate. LEDs on silicon were also successfully transferred onto flexible polyethylene-naphthalate (PEN) substrates. GaN-based LEDs on flexible substrate is a promising alternative to the current flexible organic LED displays.

HEMT devices grown on silicon were transferred to copper substrates to improve the thermal conductivity, and hence reducing the self-heating effect on the devices during high power operation. The DC drain-source current (I_ds) and transconductance (G_m) of the transistor were increased by about 25% under the same gate bias after transfer to a copper substrate. The HEMTs were also transferred to a electrical insulating quartz substrate to investigate the effects on breakdown voltage and RF performance. However, no improvement on both breakdown and RF characteristics on the devices was observed after the substrate transfer process. This is due to the low breakdown voltage of the original devices grown on silicon and possibly poor thermal conductivity of the quartz substrate.