LOW TEMPERATURE ADVANTAGES
In MOCVD, the higher temperature growth of the p-GaN top layer compared to the multi-quantum well (MQW) layer, or the active region of an LED can cause some of indium (In) to diffuse out of the active MQW layer and reduce the LEDs light output. MOCVD cannot effectively grow high performance p-GaN at lower temperatures.
RPCVD has great potential to improve device performance by growing a low temperature p-GaN layer which in turn improves the stability of the InGaN layer during growth.
RPCVD for LED MANUFACTURERS
RPCVD offers LED manufacturers many potential benefits.
The bulk of commercial LEDs are today made using a process commonly called MOCVD (metal organic chemical vapour deposition). MOCVD is a highly complex process that is used to deposit very thin layers of atoms onto a substrate to produce important compound semiconductor materials such as gallium nitride (GaN).
GaN is now an important material used in light-emitting diodes (LEDs), lasers, transistors, electronic and opto-electronic devices.
BluGlass has invented a process using remote plasma chemical vapour deposition (RPCVD), which is also a chemical vapour deposition (CVD) process, but one that offers unique advantages over the MOCVD platforms of today.
In order to explain how RPCVD is a beneficial approach to CVD, it is helpful to understand some of the basics of the incumbent technology.
How MOCVD Works
MOCVD is a method used to deposit (grow) semiconductor films onto a substrate (wafer). When producing gallium nitride (GaN), organometallic compounds are reacted with ammonia inside a deposition chamber. This gas mixture is precisely delivered to a heated substrate (up to approximately 1,200°C).
The precursor molecules undergo pyrolysis (thermal decomposition) leaving the desired atoms, e.g. Ga and N available for growth. These atoms bond at the surface and crystalline layers of GaN are formed in neatly stacked layers.
For the growth of GaN, MOCVD uses toxic ammonia (NH3) as the nitrogen source. MOCVD relies on very high temperatures to effectively break the nitrogen-hydrogen bonds to result in a quality deposition.
How RPCVD Works
RPCVD works in a similar way to MOCVD where chemicals are introduced into the reaction chamber for decomposition.
Whereas MOCVD uses ammonia (NH3) as the source of nitrogen, RPCVD uses nitrogen gas (N2) passed through an electrical coil that generates a plasma. This arrangement provides a direct source of nitrogen used for the deposition of GaN.
The nitrogen plasma generation is not dependent on high temperature to provide a source of reactive nitrogen atoms. This allows for the growth of GaN to be carried out at much lower temperatures than those used in MOCVD while maintaining the critical crystalline quality necessary for high performance devices.
Nitrogen is safer to handle and does not require scrubbing compared to highly toxic ammonia used in MOCVD.
HOW LEDs ARE MADE AND THE VALUE CHAIN