Innovative process for hydrogen exposure of silicon samples

Silicon electronic devices and other optoelectronic devices, such as solar cells, often have defects on their surfaces and within the bulk material. The defects significantly reduce device stability and efficiency. In order to reduce the effects of these defects, devices are “passivated” with hydrogen – a process that improves their performance and makes them less reactive by bonding them to hydrogen.

Oxford academics have developed technology that can introduce significant atomic hydrogen to samples by passing hydrogen through a barrier layer. Hydrogen diffuses atomically through the barrier layer and is released in an atomic form on the opposite side, which faces the sample. This can be used to passivate the defects both at the surface and in the bulk material. This has multiple advantages over current passivation techniques, and the technology is TRL 3. More details on this advanced technology can be obtained from Oxford University Innovation.

Silicon electronic devices and other optoelectronic devices, such as solar cells, often have defects on their surfaces and within the bulk material. The defects significantly reduce device stability and efficiency. In order to reduce the effects of these defects, they are “passivated” with hydrogen – a process that improves their performance and makes them less reactive by bonding them to hydrogen.

Currently, there are two commonly used techniques used to introduce atomic hydrogen to silicon. The first requires the deposition of a dielectric layer, which is commercially undesirable as the manufacturer must deposit and subsequently remove the dielectric layer if it is not used in the final device. The second technique uses a plasma exposure, which is difficult to implement as an in-line process and can also damage samples due to UV radiation and high-energy charged particles.

Oxford University academics have developed a streamlined and less damaging technology than currently available methods. The basic outline of the Oxford academics’ process is that hydrogen is introduced to one surface of the “shield”, which is a thin metallic layer, as either atomic or molecular hydrogen. The hydrogen is adsorbed and diffuses into the shield as atomic hydrogen, before moving through the shield to the opposite surface. On the opposite surface, it is re-released as atomic hydrogen that can then be used to passivate the defects in the silicon samples.

Tests have shown that significant atomic hydrogen can be passed through a metallic shield, which can lead to world-leading passivation of defects at silicon interfaces. This will improve the performance of solar cells and other optoelectronic devices.

Further development is focussed on increasing the amount of hydrogen released to the sample and demonstrating the application for passivation of bulk defects.

There are many benefits to this new technology:

  • Improved passivation of defects and device performance
  • Separating plasma and sample chambers protects sample from plasma damage
  • Hydrogen reaching the sample is neutral and low-energy so does not cause any damage itself
  • Sample and plasma chamber can be held at different pressures – allows simple in-line processing for exposing samples to atomic hydrogen
  • Simple to incorporate into any device production line
  • World-record lifetimes

The technology can be used to significantly improve the performance of anything requiring atomic hydrogen exposure, e.g. solar cells, doping of metal oxides, and in other optoelectronic devices.
The technology is at TRL level 3 and is available to license. For more information, please contact Oxford University Innovation.

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