How I can create intrinsic electric field in a device?
What is exactly this electric field in the device?
Thanks a lot
- The simplest way to create an internal (intrinsic) electric field in a device is to form a p-n junction where an electric field is built-in as a result of free carriers diffusion (free holes leaving p-type side towards n-type side and free electrons leaving n-type side towards p-type side) which gives rise to the formation of uncompensated fixed ionized acceptors on p-type side and uncompensated fixed ionized donors on n-type side. The resulting electric field at p-n junction interface is maximum at the very metallurgical junction (interface) and decreases in the bulk of n-type as well as p-type regions and vanishes in the neutral n-type and p-type regions where no more space charge is present. This internal electric field at the interface of p-n junction can be controlled by doping levels Na on p-side and Nd on n-side as well as the exact distribution of Na and Nd at the interface (abrupt p-n junction, linear p-n junction, hyperbolic p-n junction ...). With increasing Nd and/or Na the maximum electric field at the interface can be increased. However, there are two limits : one limit is on the max electric field value which is related to the energy bandgap of the material and the second is that this intrinsic electric field is strictly restricted to space charge region (SPR). Outside this region inetrnal electric field is vanishing and therefore not active.
- In order to increase this internal electric field there is a trick : to built a p-i-n junction (p-type region followed by an insulating region and finally an n-type region). In this case, the insulating region (i) which plays the role of a kind of externally controlled SPR, makes it possible to control much higher intrinsic electric fields than in the simple p-n junction. Indeed p+ - i -n junctions make it possible to reach very high ionizing electric fields in avalanche photodiodes for example. Here two versatile parameters make it possible to tailor the desired internal electric field : the doping (heavily doped p-type layer hence p+) and the width of the insulating layer.
- There are also other more complex ways to create quasi-electric fields in heterostructures by the so-called energy bandgap engineering and band-offsets engineering as developped by Herbert Kromer (Nobel prize in physics) see reference 1 and by Federico Capasso ( Owner of several patents inthis field) see reference (2) for example.
(1) Article Quasi-Electric Fields and Band Offsets: Teaching Electrons New Tricks
(2) https://ieeexplore.ieee.org/abstract/document/303697
Best regards
Professor A. Kadri
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