HVPE promises high indium content LEDs
Hydride-vapor phase epitaxy has successfully made stable In0.43Ga0.57N, giving it a great chance of becoming the leading green LED production system.
HVPE specialist Technologies and Devices International (TDI) unveiled its approach to high indium content material at the International Workshop on Nitride Semiconductors in Montreux, Switzerland on October 6.
Alexander Syrkin, deputy director at TDI, told compoundsemiconductor.net that trichlorogallium and trichloroindium precursors are critical to achieving the level of indium needed for green GaN-based LEDs.
“Temperature is the main variable that influences the indium content when used in MBE and MOCVD,” he said. “Thermal stability of InGaN is a key parameter but has a narrow range.”
By selecting precursors with the right chemical and thermodynamic behavior, TDI has been able to maintain process temperatures between 680 and 710°C, ensuring the InGaN layer stays intact.
“Our 43 percent InGaN material has been thoroughly investigated by the most renowned transmission-electron microscopy specialists in the field,” Syrkin asserted. ”We are confident that there are no indium precipitates.”
Using ammonia as the nitrogen source, TDI produced epilayers on GaN-on-sapphire template substrates at a rate of up to 2 µm/h. Simple heterostructures made from n-doped InGaN layers containing various levels of indium and p-doped GaN exhibited electroluminescence across the whole range from 450 nm to 690 nm.
As well as examining device properties, Syrkin and colleagues are continuing to investigate the physical properties of the material coming out of this latest process. Although it can make either fully strained or partially relaxed material, TDI is still working to understand what controls the relaxation.
This work continues several years of InGaN HVPE development that have helped to establish the company as a leader in the technology.
“TDI has introduced several non-traditional elements into the process and the tool that have allowed us to resolve some issues that others are still struggling to overcome,” Syrkin said.
The company s success in HVPE to date was a key factor in its purchase by Oxford Instruments, an equipment manufacturer with a strong focus on the LED industry, in April.
