corning's claims re' blg's process

Regarding Cornings claims about GaN on glass in the previous thread.

Just a reminder that their patent application makes a reference to BluGlass, ie:

“The BluGlass process entails growth of the GaN directly on glass using low temperatures (i.e., significantly lower than 1000.degree. C.).
This approach, however, results in amorphous or very fine grained polycrystalline GaN, which leads to LEDs with poor efficiency.
In addition, the glass used in this process cannot withstand high temperatures, thus limiting the deposition temperature of GaN, which again leads to poor quality material and poor LED performance”

I asked for some clarification on that statement from BLG.

Here is Stefanie Winwood’s comprehensive reply:

1. Claim : The BluGlass process entails growth of the GaN directly on glass using low temperatures (i.e. significantly lower than 1000.degC). This statement is incorrect. GaN is not grown directly on glass at temperatures significantly lower than 1000 degC. While the statement with regards to temperatures is true (any GaN on glass work done by BluGlass was deposited on glass at around 650 degC), BluGlass has always used a ZnO buffer layer between the GaN and glass substrates, for the very reasons they mention in the patent themselves (see paragraph 6).

2. Claim : This approach, however, results in amorphous or very fine grained polycrystalline GaN, which leads to LEDs with poor efficiency. If the statement above was true i.e. deposited directly on glass, then yes this would happen. However, the ZnO buffer layer better lattice matched to the bulk GaN coming on top of if and improves the quality of the bulk GaN layer.

3. Claim : In addition, the glass used in this process cannot withstand high temperatures, thus limiting the deposition temperature of GaN, which again leads to poor quality material and poor LED performance. The glass used at the time was limited to these temperatures. However, Corning themselves have a grade of glass which can go up to 750 degC. Note that the process is also compatible with silicon and sapphire, so it is only the choice of substrate that is limiting the temperature, and not the process itself. “

Cheers all.