This paper treats LED nonlinear distortions of differential gain (DG) and differential phase (DP) theoretically. Possible origins and numerical analyses are presented for AlxGa1-xAs LED's, considering various junction structures; double-heterostructure, single-heterostructure, and homostructure. It is shown that homostructure is superior to the others in linearity. The double-heterostructure is superior in optical power generation and in high-speed modulation, if the same structure parameters are adopted. The effects on linearity of doping concentrations, thermal resistance, and carrier confinement breakdown due to insufficient heterointerface barrier height are analyzed. An experimental result is shown to confirm the analyses. The results obtained will contribute to linear LED design.