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

Abstract

A typical feature of the noise characteristics of injection lasers is the appearance, at low frequencies, of a noise spectrum in which the spectral density of the fluctuations (SDF) has a frequency dependence of type I/if, where a = 1 [1][2][3][4][5][6]. The presence of noise of this kind was observed also in light-emitting diodes and in superluminescent diodes [7]. Analysis of the available published experimental data shows that a strong scatter is observed in the measured values of this excess low-frequency (LF) noise in emitters of various types. 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. It was indicated in [10] that excess currents are observed also in GaAs homolasers and can determine the level of the 1/f noise in the latter. No further experimental research, however, has been carried out along these lines.As to theoretical simulation of the noise characteristics of lasers in the LF region, the available reports [11][12] of an analysis based on the model of Voss and Clarke [11] or by using the Hooge hypothesis [12], contain neither a comparison of the results of analysis of known experimental data, nor an explanation of the observed scatter of the experimental data or a calculation of the Hooge parameters on their basis.The aim of the present paper is an exposition of the experimental results of an analysis of the relation between the excess LF I/f-type fluctuations of injection-laser power (and of several types of light-emitting diodes) with their radiative and electric characteristics. We shall present the result of an investigation of LF noise of GaAIAs heterolasers with shallow and deep stripes and of terraced lasers [16], as well as buried InGaAsP heterolasers with ridged waveguides. It will be shown that in the laser diodes at our disposal the excess LF noise is determined by the excess currents discussed above, which are nonradiating. A correlation with the level of the excess current was observed up to cases in which the frequency, at which the SDF begins to increase above white noise, amounted to 3 kHz in single-frequency lasers with laterally restricted beams, the lowest value known in the literature. A simplified theoretical analysis of the results will be carried out in light of the present nottons concerning the causes of 1/f noise in semiconductor devices. In addition, data obtained from the experimental analysis will be given concerning certain specific causes of the onset of LF n...