Light and voltage noise of lasers based on AlxGa1–xAsGaAs heterojunctions

Abstract

Light and voltage noise in AI,Gal_,As-GaAs heterolasers are studied in a wide range of forward currents (i = to 4 A) and frequencies (f = 1 to lo7 Hz). The noise characteristics obtained are compared with those observed on GaAs laser diodes. Results of investigations carried out on samples of both types are similar. Components of l/f-type are found in the spectra of light noise as well as in the spectra of voltage noise. At currents below the threshold value, these components are correlated with each other and are due t o the fluctuations of the nonradiative component of the diode current. The reasons for the changes in the l/f-noise which take place a t the sample change-over to the laser action are discussed. As the change-over to the laser action occurs, the sharp increase of frequencyindependent high-frequency light and voltage noise predicted by the theory is found experimentally. These noises appear t o be fully correlated with each other, the phase shift between the fluctuations of light and of voltage on the diode contacts being equal t o 180". I n addition, the change of the noise characteristics taking place in the course of diode operation is disclosed and analysed. As a result a connection is established between the processes of the slow laser degradation and the peculiarities of the excess component of the diode current as well as of its low-frequency noise. 41"

Analysis of low-frequency fluctuation of the radiation power of injection lasers

“…Investigations of the InGaAsP and GaA1As laser structures in the spontaneous-emission regime have confirmed the results of [8][9][10] for GaAs light-emitting diodes, namely, that in the light-emitting-diode lasing regime the excess 1/f noise is determined by nonradiative currents in the laser structures. Figures 13a, b, c, and d show CIW and the dependence of the SDF on the pump current at 1 kHz for various buried lasers and for lasers with ridged waveguides.…”

“…Our investigations cast some light on the question whether the service life of injection lasers can be predicted from the known level of the excess 1/f noise, a question posed repeatedly in the literature [5,6,10,32]. It is quite probable, since the 1/f noise reflects only the quality of the electronic structure of lasers, that it can be used to estimate only the service life connected with this quality.…”

“…An increase in excess 1/f noise was reported [10] following degradation of GaAs homolasers. Such an increase in the noise upon degradation of buried InGaAsP lasers was described by us in [29].…”

“…So far, however, no real investigations capable of revealing the cause and determining the level of the excess LF noise and its scatter have been performed. We have found only one cycle of studies of this kind, by N. B. Luk'yanchikova et al [8][9][10], who carried out such an investigation for light-emitting diodes in GaAs and GaP systems. They have shown that the excess noise with a spectrum of the i/f type observed in such devices is due to the so-called excess currents that manifest themselves at low bias by a deviation of the current--voltage characteristic (IVC) from the diffusive dependence I = I s exp(eV/(1-2)kT), where I s is the saturation current.…”