Preparation,Properties And Characterization Of Codoped P-type Zinc Oxide And N-rich Zr-N Thin Films

Zinc oxide (ZnO) is a II-VI semiconductor with a wide band-gap of 3.37 eV and a hexagonal wurtzite structure. Due to its large exciton binding energy (60 meV), it can be considered as a prime candidate for ultraviolet light emitting diodes and laser. The growth temperature of ZnO is only a half value of that of GaN, which reduces the atomic diffusion between the film and substrate. This makes it a promising candidate used in many areas, such as ultraviolet laser diodes, light emitting diode. Interest of ZnO a promising material for optoelectronic devices has intensified since the first reported in 1997 on the room-temperature ultraviolet (UV) laser emission of ZnO poly-crystallite thin films. Specifically, in the recent few years, more and more attentions have been attracted on electroluminescence.Recently many groups have reported successfully fabricating p-type ZnO. But, the fabrication of p-type ZnO exists normally the problem of high resistivity, low carrier concentration, low mobility, low doping concentration, and unstable, etc. There is a still long way to go to make p-type ZnO practicality. The key to obtain the high quality device is producible low resistivity and stable p-type ZnO.Aiming at the hot issues in current ZnO study field, in this section thesis, we focus on the the fabrication, structure, optical and electrical properties on B-N codoped and P-N codoped p-type ZnO. The major work and results are list as follow: (1) B-N codoped ZnO films were prepared on quartz substrates by r.f. magnetron sputtering method using ZnO:BN(1at%) target, using mixture of nitrogen and oxygen as sputtering gas. The effect of annealing temperature on the structure and properties of B-N codoped films was studied. Through the analysis of the experiment results, we draw this conclusion: with the increasing annealing temperature, the crystallinity is improved, the band-gap width first occur red shift and then blue shift, the conductivity of the film changed dramatically from n-type to p-type, and finally changed to weak p-type, at an intermediate annealing temperature 650°C, the B-N codoped ZnO film behaves the best p-type conductivity property, it has room-temperature resistivity of 2.3Ωcm, Hall mobility of 11 cm2/Vs and carrier concentration of 1.2×1017 cm-3, the p-type conduction comes from contribution of VZn and No acceptors. The p-type characteristics of the B-N codoped ZnO were improved remarkably as compared with N-doped ZnO fabricated under the same experiment condition. A ZnO homojunction was prepared by depositing a n-type ZnO layer on the B-N codoped p-type ZnO film and showed a rectification behavior.(2) Using magnetron sputtering technique, in argon and oxygen sputtering ambient, we discussed that the effect of oxygen partial pressure ratios on electrical properties of B-N codoped films. The hall measurement result indicate that when oxygen partial pressure ratio was 70%, the codoped ZnO film fabricated in quartz substrate at vacuum 600°C showed the best p-type conduction properties, which showed a restivity of 2.3Ωcm with a Hall mobility of 15 cm²/Vs and carrier concentration of 1.8×10¹⁷ cm^-3. The p-type behavior of B-N codoped ZnO films deposited in 70% of oxygen partial pressure ratio was confirmed by p-ZnO/n-Si heterojunction which showed a clear p-n diode characteristic. Meanwhile, the effect of post-annealing atmosphere on the properties of B-N codoped ZnO films fabricated in argon and oxygen sputtering ambient are studied. The results indicate that the hole concentration of the sample annealed in vacuum is about two order magnitudes higher than that of the sample annealed in oxygen. The p-conduction is attributed to No acceptors contribution for the B-N codoped p-ZnO obtained in vacuum and to VZn acceptor contribution for the B-N codoped p-ZnO obtained in oxygen ambient. (3) Using magnetron sputtering technique, in argon and nitrogen sputtering ambient, P₂O₅ and N₂ are served as dopant sources, the P-N codoped ZnO film fabricated in quartz substrate annealed 30 min at vacuum 800°C showed the best p-type conduction properties, which showed a restivity of 3.98Ωcm with a Hall mobility of 3.35 cm²/Vs and carrier concentration of 1.16×10¹⁸ cm^-3. The results analysis indicate that the p-type ZnO film was fabricated under Zn-rich condition, P substitute the site of Zn, N substitute the site of O in ZnO lattice to be an effective No acceptor. According to theoretical calculations in combine with the analysis of optical properties, we conclude that a passive stoichiometric (PZn–3No) complex was formed, which forms an additional fully occupied impurity band above VBM of pure ZnO, leading to the acceptor level decreasing due to the the valence band edge upward shift. The complex and an additional N atoms form a stable structure of P_Zn-4N_o complex, and the p-conduction is attributed to the P_Zn-4N_o complex acceptors contribution for the P-N codoped p-ZnO film.Transition metal nitrides,such as Zirconium nitride (Zr-N), Titanium nitride (Ti-N), etc., have been attracting much attention for various applications due to high intensity, great hardness as well as good thermal and conductive property. Many experimental results demonstrate that Zr-N compounds, produced in thermodynamic equilibrium state under atmospheric pressure, are usually poor nitrogen, and the highest N to Zr ratio is 1:1. However, preparation of N-rich Zr-N is proven difficult, and the N-rich Zr-N usually is metastable. Although it is generally difficult to fabricate N-rich Zr-N, investigation on N-rich Zr-N is interesting in theory and application. C-Zr₃N₄ film is a new and important material, but it is difficult to prepare the film. It is essential to search new method and techniques to fabricate the c-Zr₃N₄ film for its investigation in theory and application. In addition, although it is predicted in theory that the c-Zr₃N₄ is semiconductor, it is not demonstrated in experiment so far. Many studies have been performed in order to establish a relationship between the processing parameters, the film structure and properties. It is of special interest to explore the effect of processing parameters on structure and properties of N-rich nitrides. In this section thesis, we focus on the the fabrication, characterization of the structure, optical and electrical properties on N-rich Zr-N film. The major work and results are list as follow:(1) N-rich Zr-N thin film composed of c-Zr₃N₄ andγ-ZrN was deposited on Si substrates at 500°C using radio frequency (rf) magnetron sputtering technique by sputtering Zr target, using argen and nitrogen as sputtering gas, and a single phase of c-Zr₃N₄ film was grown on a glass substrate at 100°C and then annealing at 400°C under the N₂ ambient. Hall measurement indicates that the c-Zr₃N₄ compound is a p-type semiconductor with resistivity of 2.121×10⁴Ωcm, carrier concentration of 9×10¹⁴ cm^-3 and Hall mobility of 0.34 cm2/Vs. Its bandgap was evaluated to be about 2.8 eV. Formation of the c-Zr₃N₄ film is suggested to be attributed to non-equilibrium process of film growth and the action of the tensile stress induced by lattice and thermal mismatches.(2) Effects of N₂ : (N₂+Ar) flow ratio on the structure and properties of the films are systematically studied. Studies result indicate that for the Zr-N flim grown on glass at 400°C and RN₂≤20%, it consists mainly ofγ-ZrNx. The N concenttratin and lattice constant of theγ-ZrNx increase with increasing RN₂. For the Zr-N film grown on Si at 500°C and RN₂ ranging from 20 to 100%, it is composed ofγ-ZrN and c-Zr₃N₄ The relative content decrease forγ-ZrN but increases for c-Zr₃N₄ with increasing RN₂.The Zr-N film undergo from theγ-ZrN phase to c-Zr₃N₄ phase, and undergo from the conductor to the semiconductor.