Gamma ray irradiated LED's - Surface emission and significant wavelength tuning via surface states

It is pointed out that when irradiated light emitting diodes (LEDs) are operated in vacuum, wavelength tuning through shallow junction GaAs LEDs as a result of gamma irradiation is significantly increased. Vacuum operation is thought to be essentially equivalent to increased gamma ray dosage for low irradiation levels as a result of desorptive processes common to both phenomena. They cause decreased nonradiative and increased radiative components of surface recombination photon emission. This is the spectrum which is shifted according to changes in surface potential and forward voltage deriving from alterations in surface state populations. The mathematical model developed here relates wavelength tuning to surface potential and forward voltage shift. In principle, this technique is general and does not depend on the semiconductor material. It indicates the possibility of wavelength tuning through surface band-bending changes caused by surface electric field changes, as is done with MIS devices.