each of the barrier layers serving as barrier portions is made of a Group III V compound semiconductor including at least one element selected from {HEAD ~ the group} consisting of In, {TAIL ~ Al} and Ga of the Group III element and As of the Group V element 
each of the barrier layers serving as barrier portions is made of a Group III V compound semiconductor including at least one element selected from { HEAD ~ the group } consisting of In , { TAIL ~ Al } and Ga of the Group III element and As of the Group V element
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 HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH