The GaAs IR Light-Emitting Diode James R. Biard

a texas instruments snx-100 gaas led contained in to-18 transistor metal case.

in august 2013, during recollection of patent, dr. biard stated following:

the first diodes saw emitting light not designed leds. varactor diodes , tunnel diodes, had of n-type surface , p-type surface covered ohmic contact achieve low series resistance. @ time, varactor diodes had etched mesa geometry , ir light came out around edge of mesa. on tunnel diodes, light seen @ edges of chip. did not emit light, enough see ir image converter microscope. led create structure in n-type surface of chip had spaced contacts, light emitted @ junction emitted of top surface of chip. gary made spaced n-type ohmic contacts tin plating metal wires , alloying tin on surface of wire n-type gaas surface. rectangular chip of gaas, of light emitted @ junction reflected @ exit surface. index of refraction of gaas 3.6 , air has index of 1.0. means ~97% of light emitted @ junction totally internally reflected @ exit surface. highest quantum efficiency can expected rectangular led chip ~2%, anti-reflection coating on optical exit surface. total internal reflection problem led come hemispherical dome led. in diode n-type gaas substrate shaped hemisphere , hemispherical surface covered anti-reflection coating (preferably silicon nitride) minimize front surface reflection. led p-n junction in center of flat face of hemisphere. central p-type region covered anode ohmic contact. cathode ohmic contact donut shape covered of remainder of n-type flat surface of hemisphere. making diameter of hemisphere 3.6 times larger diameter of p-type layer, light @ exit surface of hemisphere inside critical angle total internal reflection. resulted in huge increase in quantum efficiency because 50% of light emitted @ junction escape chip @ hemispherical exit surface. other half of light went toward p-type ohmic contact , absorbed in gaas. absorption in thicker n-type gaas between junction , exit surface resulted in less improvement in quantum efficiency had hoped for, however, dome leds more efficient.