Abstract

Shot noise current suppression in a semiconductor junction diode driven by a high impedance source is the basis of photon noise suppression in laser diodes¹ and light emitting diodes.^2,3 A noise equivalent circuit for a light emitting diode which is consistent with the rate equations derived for laser diodes¹ as subsequently simplified for light emitting diodes⁴ is shown in Figure 1. In essence, a negative feedback mechanism reduces the injection current (recombination rate) fluctuations below the shot noise level via the fluctuating junction voltage, v(t). This voltage reflects the fluctuating charge carrier population number, n(t) = C · v(t)/e, where C represents the junction capacitance. In this “leaking reservoir” model, the noise reduction occurs over a 3 dB bandwidth, the “squeezing bandwidth”, given by ƒ 1 / (2π · r · C), the same expression as for the modulation bandwidth, where r · C = τ, the carrier lifetime. It has been suggested⁵ that the negative feedback mechanism persists as the junction capacitance is reduced and operates to regulate single electron injection through the Coulomb blockade effect⁵ in mesoscopic junctions. The macroscopic Coulomb blockade model⁵ predicts that the squeezing bandwidth will be linearly proportional to current and inversely proportional to both temperature and depletion capacitance in the low injection current regime.

© 1995 IEEE