Design parameters of frequency response of GaAs—(Ga,Al)As double heterostructure LED´s for optical communications

Cutoff frequency of GaAs-(Ga,Al)As double heterostructure light-emitting diodes (LED\´s) is investigated as functions of design parameters, such as hole concentration of the active layer, thickness of the layer, and injected current density. The cutoff frequency increases with increasing the hole concentration and injection current density, and with decreasing the active layer thickness. They are theoretically explained by the simple equation proposed in this paper by setting the recombination constant B to be 1.1 × 10^-10cm³/s. A tradeoff between the cutoff frequency and the efficiency as a function of the hole concentration is discussed. By introducing a new idea of the "figure of merit" as a product of the cutoff frequency and the efficiency, the hole concentration is optimized to be 3 × 10¹⁸cm^-3for Ge-doped active layer.