| Abstract [eng] |
Laser diodes (LDs) are compact forward biased pn junction devices. Mid-infrared spectral region 2-3 µm is considered to be “eye-safe” and multimode Fabry–Perot GaInAsSb LDs, operating in this region, are used in the field of gas sensing, medical and defense applications. Single-mode distributed feedback (DFB) InGaAsP lasers have a huge significance in the high-speed optical communication systems as they can guarantee narrow and stable spectrum of the light what enables higher transmission speed and higher data rate. Low-frequency noise spectroscopy, which is used for these lasers analysis, is nondestructive and very sensitive diagnostic tool for optoelectronic device quality evaluation and identification of nature of the degradation sources. It is well known that excess noise in semiconductor device is caused by defects and structural nonidealities. The aim of this work was to investigate DFB and FP LDs low-frequency noise characteristics, to find their relation with the device quality and reliability, to present a detailed analysis of electrical and optical fluctuations of LD by correlation method and to demonstrate various methods for laser threshold identifying. Investigated DFB laser diodes are distinguished by 1/f α-type optical and electrical fluctuations at the lasing operation. Origin of this noise is a superposition of many generation-recombination processes through defects formed centers with widely distributed capture parameters. It was shown that cross-correlation between electrical and optical fluctuations indicates presence of defects at the active region interface that forms leakage current channels, accelerates LD degradation and cause negatively correlated optical and electrical fluctuations. Decomposition of noise spectral density and cross-correlation coefficient into independent noise components (noise sources) enables evaluation of correlated (that are located in the active region) and uncorrelated (that are in the passive layers of LD) optical and electrical noise sources. Investigated FP laser diodes are distinguished by mode-hopping effect and causes intensive highly correlated Lorentzian-type optical and electrical fluctuations. Origin of those fluctuations is generation–recombination processes through defects formed centers in the barrier layers. Thus, the correlated electrical and light intensity fluctuations are related with the random potential height fluctuations of barrier layer. Also it was shown that electrical characteristics (derivative of current-voltage characteristic, conductance and capacitance) can be used for the threshold current identification. |
