Dear Dr. Xu Xuanwen,

Doping of semiconductors is achieved by introducing atoms with more or less electrons than the parent element. Doping is substitutional, the dopant atoms directly replace the original atoms. Suprisingly low levels of dopant are required, only 1 atom in 109 of the parent atoms.

Some of the Ni2+ ions have been oxidised to Ni3+ and some Ni2+ ions diffuse out to maintain charge balance leaving cation holes. The reason for the conduction is the ability of electrons to transfer from Ni2+ to Ni3+ ions. This basically allows the Ni3+ ions to move and black NiO is therefore a p-type semiconductor.

For more details, please see the source:

-Doping of Semiconductors: n-type and p-type

Available at: http://genuspolitics.blogspot.com/2008/10/doping-of-semiconductors-n-type-and-p.html

Best regards, Pierluigi Traverso.

Dear Dr. Xu Xuanwen,

Doping of semiconductors is achieved by introducing atoms with more or less electrons than the parent element. Doping is substitutional, the dopant atoms directly replace the original atoms. Suprisingly low levels of dopant are required, only 1 atom in 109 of the parent atoms.

Some of the Ni2+ ions have been oxidised to Ni3+ and some Ni2+ ions diffuse out to maintain charge balance leaving cation holes. The reason for the conduction is the ability of electrons to transfer from Ni2+ to Ni3+ ions. This basically allows the Ni3+ ions to move and black NiO is therefore a p-type semiconductor.

For more details, please see the source:

-Doping of Semiconductors: n-type and p-type

Available at: http://genuspolitics.blogspot.com/2008/10/doping-of-semiconductors-n-type-and-p.html

Best regards, Pierluigi Traverso.

The above reply is sufficiently enlightening. I want to add a simple remark. Generally if you take any semiconductor in idealistic conditions i.e., it is fully stoichiometric, there is no defects like vacancies/interstitials, no dangling bonds or valence mismanagement, then they are intrinsic; and not n or p-type.

But, in practice, to increase entropy and decrease free energy, real materials do not behave ideally. So, they become n or p-type. Most binary transition metal oxides are n-type e.g., ZnO is n-type for non-stoichiometry and Zn-interstitials. But, NiO is p-type for the reason Dr. Pierluigi Traverso has described above.

Stoichiometric NiO, a Mott–Hubbard insulator at room temperature, shows p-type electrical conduction due to the introduction of Ni2+ vacancies (VNi'') and self-doping of Ni3+ ions in the presence of excess oxygen . conductivity is vanishingly small.

Al doped NiO thin films p-type conductivity is strongly enhanced as a result of Mott-Hubbard Insular to metal transition (increasing electron-electron and hole -hole correlations together with decreasing energy bandgap.

Laser treatment of NiO thin films can convert p-type to n-type conduction. n-type conduction is not stable and decreases as a function of time.

Same bistable p-type to n-type conduction switching is also obtained by external voltage on Pt/NiO/Pt capacitor structures.

See for instance following papers:

1. Enhanced p-type conductivity and band gap narrowing in heavily Al doped NiO thin films deposited by RF magnetron sputtering

S Nandy1, U N Maiti1, C K Ghosh1 and K K Chattopadhyay1,2,3

Published 24 February 2009 • IOP Publishing Ltd Journal of Physics: Condensed Matter, Volume 21, Number 11

2. Controlled p-type to n-type conductivity transformation in NiO thin films by ultraviolet-laser irradiation

Journal of Applied Physics 111, 013706 (2012); https://doi.org/10.1063/1.3671412Pranav Guptaa), Titas Dutta, Siddhartha Mal, and Jagdish Narayan

3. Conductivity switching characteristics and reset currents in NiO films S. Seo,a!,b! M. J. Lee, D. H. Seo, S. K. Choi, D.-S. Suh, Y. S. Joung, and I. K. Yoo Samsung Advanced Institute of Technology, Suwon 440-600, Korea I. S. Byun, I. R. Hwang, S. H. Kim, and B. H. Parka!,c! Department of Physics and Research Center for Organic Display, Konkuk University, Seoul 143-701, Korea

APPLIED PHYSICS LETTERS 86, 093509 s2005d

I hope this could help you.

Best regards,

Prof. A. Kadri

A small addition to Pierluigi Traverso s reply (which I otherwise absolutely agree):

The fact whether or not Ni2+ is, in fact, reduced to Ni3+ is still a matter of debate. There actually are a number of publications that show in theory and experiment that the holes introduced by doping are rather found on the O sites:

Kuiper et al., PRL 62, 221 (1989) Article Character of Holes in Li x Ni 1 − x O and Their Magnetic Behavior

Kunes et al., PRB 75, 165115 (2007) Article Local correlations and hole doping in NiO: A dynamical mean-...

Recent insights into the nature of the valence band states of NiO (-> Zhang-Rice bound doublets, see Taguchi et al., PRL 100, 206401 (2008) Article Revisiting the Valence-Band and Core-Level Photoemission Spe...

Article Interplay of charge-transfer and Mott-Hubbard physics approa...

Thank you very much Pierluigi Traverso. Your answer is very clear.

Thank you very much Dr. Pierluigi Traverso, your answer is very clear.

Thank you very much Dr. Abderrahmane Kadri . I got so useful information from you.

Thank you very much for your explanation Dr. Souvik Bhattacharjee .

Thank you very much for your recommendation Dr. Robert Karsthof .

You are most welcome Dr Xu Xuanwen, it is indeed a very intersting question.

NiO is a two six compound semicondcutor. If It is perfectly order in the material the material will be intrinsic such that the electron concentration equals that of the hole concentration. Depending on the growth or the deposition conditions of the material a departure from perfect order occurs leading here in case of NiO to vacant Ni sites which will lead to deficiency in valence electrons leading to formation of holes. If five valence impurity atoms replace the oxygen atoms then also holes will be formed.

Doping is achieved by substituting native atoms with the suitable valency impurity atoms. It is so the intentional addition of impurity with the suitable valency. For p type the valency of the doping atoms must be smaller by one valence electrons.

For n type the opposite is true.

Best wishes

In case of metal oxides, the oxygen vacancies and metal interstitials are believed to be responsible for the p-type nature of the oxides. In order to compensate the charge due to donor defects the fermi level shifts down to the valance band.

I quite agree with Abdelhalim Zekry that p-type depend on the growth and deposition parameters , some ]times it depends of kind of technique used .this could be happens when NiO suffer a vacant of Ni it lead to decrease the oxygen and leads to for holes . if you need to use a dopant material and tou need to keep the p- type conductivity toy must emloying a a material with on valance smaller than the matrix

When NiO is stoichiometric with no defects, vacancies, interstitials, no dangling bonds (not amorphous/polycrytalline) would ideally be intrinsic and undoped.

To make a p-type semiconductor there is a critical answer for you in this paper.

At very low PO2 values, oxygen vacancies and electrons are

predominant, which also results in a slope of −1/6 in the log–

log plot (the bottom portion of Fig. 1). At intermediate PO2

values, the slope changes from −1/6 to −1/4. The oxygen va-

cancy concentration is then fixed by the acceptor content:

2[V9

Sr] + [A8] ≈ 2[VO#] (23)

Whether these acceptors originate from impurities that show

acceptor character ([A8] @ [V9

Sr]

8,9) or whether they are frozen-

in cation vacancies that form during sintering ([V9

Sr] @ [A8]

25)

is still under discussion. Applying Eq. (2), the −1/4 slope can

be calculated easily. After passing an intrinsic conductivity

minimum, where contributions by electrons and holes must be

equal,

nmn 4 pmp (24)

the sample becomes a p-type conductor. Combining Eq. (23)

with the generation/recombination equilibrium (Eq. (7)), hole

density and conductivity both increase as PO2 increases (slope

4 +1/4).

Dear Dr Xu Xuanwen

If you want to understand why as-grown NiO is p-type?, it is extremly useful to compare it with ZnO which is as grown n-type.

Why?

Because these two materials are quite similar though with radically different structural and electronic properties.

- Both NiO and ZnO are transition metal oxydes with very close energy bandgaps in the near UV: Eg=3.9eV in NiO and Eg=3.35eV in ZnO.

- However, NiO is Rocksalt with sixfold cubic symmetry, and with incomplete electronic d-shell (8 electrons),

- ZnO is Würtzite with fourfold tetrahedral hexagonal symmetry and with several characteristic properties of its own as piezoelectricity, 2DEG electron acculmulation,...and with full electronic d-shell (10 electrons)

The comparison of these two materials is better done if we study their NiMgO and ZnMgO ternary alloys properties when combined with MgO, a rocksalt insulating ceramic with a direct energy bandgap Eg=7.8eV and with only s- and p-shells electrons (no d-shell electrons).

- several groups have studied experimentally and theoretically NiMgO alloys and have shown that NiMgO is Rocksalt in the whole alloy composition range between NiO and MgO. Moreover, NiMgO remains insulating at high Mg-contents (>50%) and turns out progressively p-type in the low Mg-range contents (

Even some metals (pure ones) have a two-carrier conductivity. For example, in aluminum, which has 3 valence electrons, only two of them can become free. The third tunnels through a potential barrier to a neighboring atom, due to the overlap of their wave functions. This is how a hole appears.

The presence of holes in Al is proved experimentally by measuring the Hall effect and magnetoresistance.

One metal oxide material, nickel oxide (NiO), is a candidate for p-type transparent conducting films be- cause it is a p-type semiconductor with a band gap energy from 3.6 to 4.0 eV