Studies of the Uniformity of Avalanche Breakdown by Means of Low Frequency Noise Measurements

The correlation between low frequency noise and the uniformity of the current distribution in avalanche diodes is investigated. It is found that small diodes with a uniform current distribution obey the theoretically predicted relation u2/Δf=a2Vb2/I with a2 = 4.8·10-20 A/Hz. Larger diodes exhibit excess noise above the theoretically predicted minimum noise. The origin of this excess noise is traced to nonuniformities of the breakdown voltage across the avalanche junction. To characterize the uniformity of breakdown we have defined four quantities which can be determined readily from noise and impedance vs current characteristics. These four quantities are: (1) the number of noise peaks N; (2) the maximum noise figure F*AD; (3) the relative breakdown voltage spread ΔVb/Vb; and (4) the impedance ratior r. The correlation between these quantities and the uniformity of avalanche breakdown is demonstrated on a series of alloyed, planar, and guard ring diodes.