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  • How is the metallization of photodiode pads constructed ?

    The pads on Albis photodiode chips are built from a stack of different metals. On the chip front-side we offer two different stacks. The first stack alternative is optimized for wire-bonding. It consists of an adhesion layer followed by 1.3 µm of pure gold. The second alternative is optimized for soldering. Again it consists of an adhesion layer followed by a Platinum layer that acts as solder barrier (aka under-bump metallization). The Platinum layer is covered with 0.1 µm of pure gold to protect the pad from corrosion and secure solder wettabiliy also after extended periods of storage.

  • What is the cut-off wavelength of GaAs photodiodes ?

    The long end of the spectral response of GaAs photodiodes is limited by the bandgap energy of GaAs which is 1.42eV (corresponding to about 870nm). Hence incoming light with a wavelength beyond that limit (i.e. light with a larger wavelength) will not be absorbed as GaAs is transparent for such wavelengths. In the wavelength region from  830nm to 860nm Albis’ GaAs photodiodes have an excellent quantum efficiency close to one and hence a responsivity  up to 0.6 A/W. Below 830nm the quantum efficiency decreases gradually due to recombination losses at the semiconductor surface.

  • Why are you not using 175°C 2xVop for the qualification of the InGaAs PIN ?

    Our HTO test condtions for the qualification are 2000h at 100°C and 2 x Vop which is typically 2 x 2.0 V. Doing so, we apply Telcordia GR-468 Issue 2 Requirements. The underlying assumption for our test conditions are:

    The dominant failure mechanism that will be observed for our PIN diodes is wearout failure and not random failure. Therefore, the test condition of 2000h at 175°C do not apply for our photodiodes. Please refer to Telcordia GR-468 Issue 2, Table 4-5, Note 2.

    Telcordia GR-468 Issue 2 states in section 3.3.3 that the required test temperature for uncontrolled (UNC) environments is 85°C or the maximum specified operating temperature. We specify a maximal operating temperature of 85°C for our PIN diodes.

    However, we take into consideration that most of our photodiodes are operated at higher temperature when they become part of a package which may run 85°C ambient temperature. Therefore, we test at 100°C.

  • What is the cut-off wavelength of InGaAs photodiodes ?

    The long end of the spectral response of InGaAs photodiodes is limited by the bandgap energy of InGaAs which is 0.75eV at room temperature (corresponding to about 1620nm). Hence incoming light with a wavelength beyond that limit (i.e. light with a larger wavelength) will not be absorbed as InGaAs is transparent for such wavelengths. In the wavelength region from  1260nm to 1620nm Albis’ InGaAs photodiodes have an excellent quantum efficiency. Below 1260nm the quantum efficiency decreases gradually due to recombination losses at the semiconductor surface.

  • What is the optimal operation bias point of avalanche photodiodes ?

    The most common understanding of the optimal operation bias point is the bias condition for best receiver sensitivity. The receiver, in particular the TIA and the parasitics, will have an important impact on finding this optimal condition. The optimal bias for our 10G APD is around a multiplication gain of M=10. Using an appropriate TIA, our 10G APD achieves a receiver sensitivity of -28dBm. For the 2.5G APD the optimal multiplication gain is between M=10 and M=15. Using an appropriate TIA, our 2.5G APD achieves a receiver sensitivity of -35dBm.

    The bias voltage corresponding to a multiplication gain of M=10 is found around 90% of the breakdown voltage.

  • Are your photodiodes suited for non-hermetic packages ?

    Since more than a decade our photodiode products have been used by many different customers in a large number of different non-hermetic packages which all passed the Telcordia qualification. In most of this cases the assembly of the photodiode is offering some sort of protection against humidity.

  • How do you qualify your wire-bondable pads?

    For each wafer with wire-bondable pads we perform sample based bond-pull tests. Our test standard is MIL-STD-883E Method 2011.7.

  • How do you test your photodiodes before shipment?

    Before shipment, all photodiodes are 100% tested on wafer level and are subject to out-going visual inspection.