Preparation Of P-type ZnO Films Research Articles

Oxygen vacancy-passivated ZnO thin film formed by atomic layer deposition using H2O2

Intrinsic defect oxygen vacancies, which can easily form in ZnO films and result in a compensation effect on p-type dopants, have long prevented the preparation of high-quality p-type ZnO; consequently, the application of ZnO in optoelectronic devices has been adversely affected. Therefore, in this investigation, the passivation of oxygen vacancies in undoped ZnO using H2O2 as an oxygen source is studied using atomic layer deposition (ALD). The ALD growth window ranged from 60 to 150 °C, and the use of H2O2 as an oxygen source, instead of H2O, changed the preferred growth orientation from coexisting a- and c-axes to only the c-axis, which indicated that H2O2 can provide an oxygen-rich environment for the growth of ZnO. Photoluminescence results indicated that oxygen vacancies in the ZnO film reduced significantly when H2O2 was used as the oxygen precursor instead of H2O for film preparation. Further, oxygen vacancies can be suppressed more efficiently using H2O2 when ZnO films were deposited at lower temperatures than at high temperatures. A decrease in the optical bandgap and an increase in the work function were observed when films were prepared using H2O2 due to a lowering of the Fermi level. Therefore, the use of H2O2 as an oxygen source is effective in providing an oxygen-rich environment and passivating oxygen vacancies in ZnO, which might be beneficial for the preparation of p-type ZnO films.

Low temperature method to passivate oxygen vacancies in un-doped ZnO films using atomic layer deposition

Owing to oxygen vacancies, the as-prepared ZnO normally shows n-type semiconducting characteristic. This has restricted the preparation of high-quality p-type ZnO and the application of ZnO optoelectronic devices. Therefore, we studied a method of using H2O2 as an oxygen source to passivate oxygen vacancies (Vo) in ZnO films via atomic layer deposition (ALD). The temperature range for the self-limited growth of crystalline ZnO thin films by ALD using diethylzinc and H2O2 was found to be in the range of 80 to 150 °C. Our results show that the use of H2O2 as an oxygen source can provide an O-rich condition (instead of H2O) for the growth of ZnO film, with a total preferential (002) orientation of the growth plane and decreased grain size. Further, the O-rich growth environment can suppress the formation of Vo and zinc interstitials and decrease the carrier concentration in ZnO (from 2.525 × 1019 cm−3 to 1.695 × 1012 cm−3). This can lead to an increase in the film resistivity from 1.717 × 10−2 Ω·cm for a ZnO film prepared using H2O to 1.348 × 104 Ω·cm for a ZnO film prepared using H2O2. Thus, H2O2 could be used to passivate Vo in ZnO at a low temperature, and it could be beneficial for the preparation of p-type ZnO films.

Preparation of p-type ZnO Films by Alternate Deposition of ZnO and Mg3N2 Films

Films were deposited on a glass substrates heated at 100°C by alternate deposition of ZnO and Mg3N2 films in an atmosphere of N2 + 0.2% O2. p-type ZnO films with the resistivity of 9.9×103 - 4.5×103Ωcm were grown by Mg3N2 sputtering for 0.2s at 50-70W, whereas an n-type ZnO film was grown for 0.2s at 90W. Appearance of the n-type ZnO film is caused by a decrease of O2-partial pressure in an atmosphere. The contraction of the c-axis due to the incorporation of Mg atoms is found in these p-type and n-type ZnO films. When the Mg3N2-depostion period was extended to 5s, p-type ZnO films were grown in the alternate sputtering at 50W, whereas only insulator films were grown in the alternate sputtering at 70W. The optical band gap of the films increases with both a RF power and a period of Mg3N2-deposition.

Preparation of p-type ZnO films with (N,Ga) co-doping by MOVPE

We investigate the p-type doping in ZnO prepared by metal–organic vapor phase epitaxy, using dimethylhydrazine (DMHy) as a nitrogen dopant source. Results obtained from X-ray photoelectron spectroscopy show that DMHy exhibits a narrow temperature window from 500 to 550 °C for efficient nitrogen doping. Additional co-doping with Ga significantly enhances the nitrogen incorporation and the conductivity type of the co-doped ZnO film is critically influenced by N/Ga flux ratio in growth. The fabricated p-type ZnO film shows a hole concentration of about 2.41 × 10 18 cm −3 and hole mobility of about 4.29 cm 2 V −1 s −1. The corresponding nitrogen acceptor level is calculated to be about 160 meV from the PL spectrum. I– V characterization of a p-ZnO:(N,Ga)/n-ZnO homojunction shows clear rectifying behavior with a turn-on voltage of about 3.7 V.

Pulsed-laser-deposited p-type ZnO films with phosphorus doping

We report the preparation of p-type ZnO thin films on Al2O3(0001) substrates with phosphorus doping by pulsed laser deposition using Zn3P2 as the dopant source material. The results of the Hall effect measurements taken at room temperature indicate that the 3-mol% phosphorus-doped ZnO films thermally annealed at temperatures between 600 and 800°C under an O2 atmosphere exhibit p-type behavior with a hole concentration of 5.1×1014−1.5×1017cm−3, a hole mobility of 2.38−39.3cm2∕Vs, and a resistivity of 17−330Ωcm. The low-temperature (15K) photoluminescence results reveal that the peak related to the neutral-acceptor bound exciton (A0,X) emission at 3.358eV is only observed in the films showing p-type behavior. Our results not only demonstrate that there is a narrow temperature window for rapid thermal annealing in which phosphorus-doped p-type ZnO films can be obtained, but also suggest that the use of Zn3P2 can provide an effective approach to the preparation of p-type ZnO films.

Preparation of p-type ZnO films by Al+N-codoping method

p-Type ZnO thin films with c-axis orientation have been prepared in N 2O+O 2 atmosphere on glass substrates by DC reactive magnetron sputtering, and with the Al+N-codoping technique, we have realized p-ZnO in the same conditions. Results showed that types of conduction and carrier density in codoped ZnO films were found to be dependent on the substrate temperatures. At 500°C, both Al+N-codoped p-type ZnO films and N-doped ones have the highest hole density of 1.1×10 17 and 6.7×10 14 cm −3, respectively. When the growth temperature is higher than 550°C, p-type ZnO films cannot be achieved using the Al+N-codoped method. It is difficult to achieve p-ZnO with both high hole concentration and high mobility by codoping, most likely due to the inherent defects of the AlN precipitates produced in codoping process.

Preparation of p-Type ZnO Films by Doping of Be−N Bonds

Preparation of p-Type ZnO Films by Doping of Be−N Bonds