Hydride VPE Suitable For Quantum Wells, Says TDI
Hydride vapor phase epitaxy (HVPE) can now be used to produce very thin layers of GaN and AlGaN quantum wells, according to US-based materials specialist Technologies and Devices International (TDI).
Until now the technique, which can deposit material much faster than either MBE or MOCVD, had only been suitable for growing very thick semiconductor layers.
Engineers at the Silver Spring, MD, company say that a new HVPE machine is able to slow down from its normal deposition rate of around one micron per minute (see related article) by more than two orders of magnitude.
This means that the same machine can be controlled to grow sharp heterostructure layers just 1 nm thick, as well as much thicker layers, such as that of the GaN material in GaN-on-sapphire templates.
TDI president Vladimir Dmitriev said, "This opens up a completely new path for the formation of low-defect substrate materials and device structures."
Scientists at Arizona State University (ASU) and Virginia Commonwealth University (VCU) have characterized material grown in the novel HVPE machine. Subhash Mahajan from ASU was surprised by the success: "We never expected this technology to produce nanometer-thick GaN layers and multi-layer structures."
"However, our transmission electron microscopy (TEM) measurements proved that it [has been] achieved."
VCU's Michael Reshchikov added, "This is definitely the first HVPE-grown AlGaN/GaN structure that clearly shows a quantum well signature in photoluminescent characterization."
Although no details of defect densities are quoted by TDI or the characterization specialists, the new approach could, in theory, allow much faster manufacture of GaN-based devices than is currently possible.
As well as depositing material at up to one micron per minute, HVPE consumes less ammonia gas in LED manufacture than MOCVD. According to Glenn Solomon at NIST, HVPE also leads to fewer point defects in deposited material than MOCVD (see related magazine article).
Those in the GaN community will soon have a chance to investigate the new approach for themselves. TDI says that it plans to release epitaxial products based on HVPE-grown superlattice structures and quantum wells in early 2007.
The company will also be demonstrating multi-quantum well epiwafers and reporting its recent findings at the International Workshop on Nitride Semiconductors, which will take place in Kyoto, Japan, on 22-27 October.