Stable P-type semiconducting behaviour in Li and Ni codoped ZnO
A method is provided for growing a stable p-type ZnO thin film with low resistivity and high mobility. The method includes providing an n-type Li—Ni co-doped ZnO target in a chamber, providing a substrate in the chamber, and ablating the target to form the thin film on the substrate.
1. A method for forming a structure, comprising:
growing a stable p-type lithium (Li) and a transition metal codoped zinc oxide (ZnO) thin film, comprising:
providing Li and the transition metal codoped ZnO target in a chamber;
providing a substrate in the chamber; and
ablating the target to form the thin film over the substrate.
2. The method of claim 1 , wherein the transition metal is nickel (Ni).
3. The method of claim 2 , wherein the target has a formula of Zn 1−x−y Li x Ni y O, where x ranges from 0.01 to 0.03 and y ranges from 0.01 to 0.02.
4. The method of claim 3 , wherein x is 0.02 and y is 0.02.
5. The method of claim 2 , further comprising forming the target, comprising:
mixing and grounding lithium carbonate, nickel oxide, and zinc oxide to form a mixture;
heating the mixture at about 750° C. for about 12 hours;
grounding and pressing the powder into pellets; and
sintering the pellets at about 950° C. for about 15 hours to form the target, the target having n-type conductivity.
6. The method of claim 2 , further comprising evacuating the chamber to about 4*10 −6 millibar.
7. The method of claim 6 , further comprising introducing oxygen into the chamber to a partial pressure of about 0.15 millibar.
8. The method of claim 7 , further comprising heating the substrate to about 400° C.
9. The method of claim 2 , further comprising rotating the target.
10. The method of claim 2 , wherein the target is ablated with a pulsed laser operated at a wavelength selected from a range of 193 to 355 nanometers, with an energy selected from the range of 85 to 100 millijoules/pulse, at a pulse width selected from a range of 5 to 25 nanoseconds, at a frequency selected from a range of 1 to 10 hertz, a laser fluence selected from a range of 2.5 to 3.0 joules/cm 2 , and for a duration selected from a range of 5 to 30 minutes.
11. The method of claim 10 , wherein the wavelength is 355 nanometers, the energy is 85 millijoules/pulse, the pulse width is 19 nanoseconds, the frequency is 10 hertz, a laser fluence of 2.7 joules/cm 2 , and the duration is 10 minutes.
12. The method of claim 1 , wherein the thin film comprises, at room temperature, a resistivity selected from a range of 0.01 to 1 Ωcm, a hole concentration selected from a range of 10 17 cm −3 to 10 18 cm −3 , and a mobility selected from a range of 80 to 250 cm 2 V −1 s −1 , the hole concentration remaining within ±20% of an initial value for about 100 days after the thin film is deposited.
13. The method of claim 12 , wherein the resistivity is about 0.15 Ωcm, the hole concentration is about 3.2*10 17 cm −3 , and the mobility is 130 cm 2 V −1 s −1 .
14. The method of claim 1 , further comprising:
prior to growing the thin film:
forming a ZnO buffer layer over the substrate; and
forming an n-type ZnO layer over the ZnO buffer layer, wherein the thin film is grown over the n-type ZnO layer; and
after growing the thin film:
forming a first electrode coupled to the n-type ZnO layer; and
forming a second electrode coupled to the thin film.
15. The method of claim 14 , wherein the thin film comprises, at room temperature, a resistivity selected from a range of 0.01 to 1 Ωcm, a hole concentration selected from a range of 10 17 cm −3 to 10 18 cm −3 , and a mobility selected from a range of 80 to 250 cm 2 V −1 s −1 , the hole concentration remaining within ±20% of an initial value for about 100 days after the Li and the transition metal codoped ZnO layer is deposited.