Electron-hole recombination suppression

[Moreno]

What can efficiently suppress electron-hole recombination in some materials?

Let say we want to create a conductor with good electron and hole conductivity simultaneously.

If we will dope semiconductor with an equal amounts of acceptor and donor admixtures, they will simply recombine and bring conductivity to a low level.

Are there some exotic materials or materials with an exotic band structure where electron-hole recombination would be completely suppressed? For example, what about materials with inverted band structure similar to HgTe? Also, can hole and electron recombine if the hole have higher energy than the electron? In which cases recombination in some material can be prevented even if more electrons and holes are injected in material than there initially was?

We can also regard metals and semimetals for this purpose, not only semiconductors.

Edited March 31, 2017 by Moreno

[Bender]

Ionic bonds almost completely avoid recombination...

[Moreno]

Ionic bonds almost completely avoid recombination...

So, how exactly could be useful? I meant hole conductivity, not ionic conductivity...

 

Ionic conductors experience another problem - dissociation...

Edited April 1, 2017 by Moreno

[Bender]

I must admit that I have no idea about the type of exotic material you ask about. I thought that a ionic materials would indicate why it might be unlikely: if you want to avoid electrons from recombining with holes, don't you end up restraining them from moving at all?

 

Unless you dissolve the ions in water, then you have both positive and negative charges moving around.

 

But it is possible something like this exists but I just haven't heard about it.

[Moreno]

I must admit that I have no idea about the type of exotic material you ask about. I thought that a ionic materials would indicate why it might be unlikely: if you want to avoid electrons from recombining with holes, don't you end up restraining them from moving at all?

 

 

Why? For example, metals which belong to 2 group of periodic table, such as Beryllium, Magnesium, Zinc and many others have large overlap in valence and conduction band. Subsequently, they can conduct both electrons and holes. I don't know which exactly recombination processes can happen there.

[Enthalpy]

Most (all?) metals have at the same time many holes and many electrons, which is possible because the Fermi level passes through several bands which have opposed curvatures.

 

Big conductivity is found in metals, as they have more electrons or holes that even heavily doped semiconductors.

 

If the valence and conduction bands are well separated as in semiconductors, equilibrium wants either electrons or holes but not many of both at the same time. Though, a significant density of both exists far from equilibrium, as limited by recombination, for instance in a laser diode or in a saturated bipolar transistor - but the carriers are never as dense as in a metal.

 

I can't think of a means to suppress recombination. In many devices, designers seeks to minimize it: nonradiative recombination in light emitters, pair generation in blocking diodes... but the material itself shows a minimum rate of generation and recombination, even when not overshadowed by parasitic processes which are difficult to minimize.

 

In short: if copper and silver don't suffice, go to superconductors.

[Moreno]

If the valence and conduction bands are well separated as in semiconductors, equilibrium wants either electrons or holes but not many of both at the same time. Though, a significant density of both exists far from equilibrium, as limited by recombination, for instance in a laser diode or in a saturated bipolar transistor - but the carriers are never as dense as in a metal.

Can there be such an exotic band structure, for example: valence and conduction bands at the top which overlap each other, then - large band gap and then one more valence and conduction band overlap at the bottom? Or this is unlikely? I know that some materials - for example transitional metals have more than one conduction band (such as s and d bands), though they usually do overlap...

In short: if copper and silver don't suffice, go to superconductors.​

 

What will happen if in material similar to copper or silver number of both electrons and holes will suddenly increase? Is there going to be some kind of radiative or non-radiative recombination associated with energy release? And what about superconductors?

Edited April 2, 2017 by Moreno