Excess noise, measurable characterization

The frequency distribution of noise is characterized by a power spectrum. There a two types. First, white noise, whose noise power is independent of the frequency. This noise arises from the statistics of electrons or photons and of the thermal energy of conductors. White noise can be reduced by extending the measuring time. Second, excess low frequency noise, flicker, or 1// noise is due to fluctuations, drift and schlieren. It can be reduced by modulation. All types of noise are reduced by multiplex procedures, multichannel techniques, and multiple recording (Schrader, 1980). 

Qualitative characterization of the excess noise is possible with the use of noise spectral density at given frequency (Sikula et al. 1994). In our investigation, the measurable quantity is an indicator of sample quality and reliability Cq given as... 

Heterostructure and bipolar devices as lasers, diodes, solar cells (Chobola 2001) and transistors (Koncza-kowska 1987) are similar from the point of view of the physical processes, taking place during the device operation. This infers that the basis of the methods of their quahty testing can be similar for all of them. The main source of noise is the excess current which has 1/f spectral density. Occasionally the g-r noise, created by burst processes, is observed. Qualitative characterization of the 1/f excess noise is possible with the use of generalized Hooge s formula (6). The measurable quantity of sample quality and reliability is the indicator Mg given by... 

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