On the substrate, a first type conductivity layer, a first main layer such as {HEAD ~ an active layer}, which has any one of an undoped type, a first type conductivity and a second type conductivity, and a second type conductivity layer are formed in {TAIL ~ this order} 
On the substrate , a first type conductivity layer , a first main layer such as { HEAD ~ an active layer } , which has any one of an undoped type , a first type conductivity and a second type conductivity , and a second type conductivity layer are formed in { TAIL ~ this order }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL