Failure mode analysis of planar zinc-diffused In0.53Ga0.47As p-i-n photodiodes

Abstract

In order to understand the irreversible failure mechanisms of planar InGaAs p‐i‐n photodiodes, 32 devices from 19 different wafers that shorted during aging were first examined in the scanning electron microscope. Included were devices that failed during long term aging (>10³ h) as well as those that failed during short term aging (2 h) at higher reverse bias. With a few exceptions, the diodes failed as a result of a single localized leakage source located at the perimeter of the p‐n junction. Three types of leakage sources were found: (a) a microplasma, (b) a microplasma associated with a region of high recombination rate, and (c) a microplasma associated with a thermally damaged region. Analysis of ∼40 devices before and after aging shows that leakage paths found after aging result from microplasmas initially present in the device. Defect analysis shows that neither threading dislocations nor misfit dislocations are generally responsible for these microplasmas. Analysis of the processing shows that the p‐contact/semiconductor interface is stable during device operation. Thus, the leakage source, attributed to contact migration in other studies, is not present in our devices. However, pinholes in the SiN_x diffusion mask close (p‐n junction were found to be the major source of microplasmas. The high‐electric field at the shallow (≲0.5 μm) p‐n junctions formed by unintentional diffusion through the dielectric pinholes is believed to cause the microplasmas. Electron‐hole pairs, recombining at the microplasma site, are believed to create defects. These defects were observed as a localized region of enhanced recombination in electron‐beam induced current (EBIC) images of the p‐n junction without applied bias. The enhanced leakage current as a result of the defects leads to thermal runaway.