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On 2 October 2017 at 12:47, Wenting Guo  wrote:

> Dear ALL,
>
> I've currently met a problem related to the wet etch of GaAs/AlAs
> (6nm)/GaAs structure.
>
> We have ohmic contacts (Pd/Ge) on the top and the bottom GaAs layer
> annealed. They behave well with linear IV curve at room temperature and
> with giga ohms at the liquid nitrogen temperature if one contact is at the
> bottom while the other on the top.
>
> Then I wet etched (H2O:H2O2;H2SO4=80:8:1) around the ohmic contacts on the
> top down to the bottom GaAs while keeping the ohmic contact at the bottom
> untouched. Afterwards, I measured the resistance between the top contact
> and the bottom contact again. However, the result shows that they are short
> through the AlAs layer now.
>
> I tried different combinations of the Pd/Ge thickness (25/75 nm -> 25/15
> nm) and the annealing temperature from 350C to 200C. The same short appears
> again and again,
>
> Is that possible the wet etchant somehow damage the AlAs layer? I'm running
> out of ideas for the moment. Could anyone kindly give me some suggestions
> about this?
>
> Many thanks,
> Best wishes,
> Wenting
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