also exhibits optical gain referring to fig5 a in another embodiment of the light emitting device 10 the e part includes a led the b part is a resonant tunneling rt barrier in series with a thin lt gaas layer and the c part is a metal schottky barrier the b part is constructed so that the first confined energy level within the quantum well qw is below the conduction band of the e part and so that the second confined energy level is above the conduction band of the e part one technique to operate this embodiment of the device 10 is with the e b part biased with the dc power supply while the b c part is optically modulated when no light is incident on the surface of the b part electrons injected into or generated within the e part are confined to the e part under these conditions the device emits 10 light with maximum efficiency as minority carriers are confined to the e part in the same manner as the embodiments of fig3 and 4 when light with energy greater than the bandgap energy of the b part is incident and absorbed in the near surface of the b part electron hole pairs are generated electrons drift into the metal region of the schottky barrier thermalize to the fermi level and impose a negative charge on the metal while the holes drift toward the e part the resulting charge separation induces a change in the electric field in the b region thereby causing less band bending than in the non illuminated case in the embodiment of fig5 c the decrease in band bending.