PROCEEDINGS ARTICLE | June 12, 2001

Proc. SPIE. 4288, Photodetectors: Materials and Devices VI

KEYWORDS: Avalanche photodetectors, Gallium arsenide, Silicon, Solids, Ionization, Diodes, Aluminum, Gallium, PIN photodiodes, Reverse modeling

The avalanche multiplication noise characteristics of Al_{x}Ga_{1-x}As (x equals 0-0.8) have been measured in a wide range of PIN and NIP diodes. The study includes determining the effect of the alloy fraction, x, as it varies from 0 to 0.8 while the effect of the avalanche width, w, is investigated by varying it from 1 micrometers down to 0.05 micrometers . For x equals 0-0.6, the ratio of the electron to hole ionization coefficients, 1/k, decreases from 3 (for x equals 0) to 1 (for x equals 0.6), leading to higher noise in a local prediction as x increases. Measurements for x equals 0-0.6 in nominally 1um thick diodes indicates that the excess noise factor can be approximately predicted by the local model. However, as the avalanche width reduces, a lower than expected noise factor was measured. This behaviour is associated with the effect of deadspace, whereby carriers have insufficient energy to initiate ionization for a significant region of the device. The presence of deadspace leads to a more deterministic process, which acts to reduce excess noise. For x equals 0.8 however, its 1/k value is surprisingly high in a bulk structure, leading to noise performance that is primarily determined by the 1/k value and is comparable to that of silicon. Similar to the results of thin Al_{x}Ga_{1-x}As (x equals 0-0.6) diodes, thinner Al_{0.8}Ga_{0.2}As structures exhibit excess noise factor that is significantly reduced by the nonlocal deadspace effects.