If the layer is too thick the advantage of {TAIL ~ confinement} is lost, and if the layer is too thin carrier spillover may occur, both of which contribute negatively to the efficacy of {HEAD ~ a solid state lighting source} 
If the layer is too thick the advantage of { TAIL ~ confinement } is lost , and if the layer is too thin carrier spillover may occur , both of which contribute negatively to the efficacy of { HEAD ~ a solid state lighting source }
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD