Gamma Ray Irradiated LED's: Surface Emission and Significant Wavelength Tuning Via Surface States

Wavelength tuning via shallow junction GaAs LED's as a result of gamma irradiation is increased significantly when the irradiated LED's are operated in vacuum. Vacuum operation is seen to be essentially equivalent to increased gamma ray dosage for low irradiation levels as a result of desorptive processes common to both phenomena. They give rise to decreased nonradiative and increased radiative components of surface recombination photon emission. It is this spectrum which is shifted according to changes in surface potential and forward voltage deriving from alterations in surface state populations. A mathematical model is developed to relate wavelength tuning with surface potential and forward voltage shift. This technique is, in principle, a general technique independent of semiconductor material. It suggests the possibility of wavelength tuning via surface band-bending changes deriving from surface electric field changes, as is done with MIS devices. Examination of irradiated diode properties in vacuum and under pressure permits greater insight into the basic nature of surface phenomena long suspected to play a significant role in the diode electronic property changes brought about by nuclear irradiation.