Features of Barrier Capacitance of Micropixel Avalanche Photodiodes at Different Frequencies

There has been investigated the capacitance of silicon micro pixel avalanche photodiodes (MAPD 3N) with deeply buried pixels under the effect of weak AC signal of different frequency (from 10 kHz to 1 MHz). A decreasing of the barrier capacitance with an increasing of AC signal frequency has been observed when small DC bias voltage (0-3 V) is applied to the structure. With the rise of voltage the observed dependence weakens and further saturates. It is established that capacity behavior like this within small voltage is referred to the peculiarity of MAPD structure under the investigation: presence of matrix of n + -regions between two epitaxial layers of p-type conductivity results in the appearance of some effective resistance between these layers connected in series with the measured capacity depending on AC signal frequency. The calculated values of ionized acceptor concentration from the slope of the dependence C -2 (U bias ) in epitaxial layer are: N A1 = (2.4 ±0.3)∙10 20 m -3 for U bias up to 3 V, N A2 = (1.08±0.05)·10 21 m -3 for U bias from 3 to 10 V and N A3 = (2.13±0.27)∙ 10 21 m -3 for U bias from 10 to 20 V respectively.