Effects of annealing ambience on ZnO:N films grown by MOCVD and the p-type doping mechanism of ZnO:N films investigated by XANES

ZnO:N thin films were deposited on sapphire substrate by metal organic chemical vapor deposition with NH₃ as N-doping sources. The reproducible p-type ZnO:N film with hole concentration of ∼10¹⁷ cm⁻³ was successfully achieved by subsequent in situ thermal annealing in N₂O plasma protective ambient, while only weak p-type ZnO:N film with remarkably lower hole concentration of ∼10¹⁵ cm⁻³ was obtained by annealing in O₂ ambient. To understand the mechanism of the p-type doping behavior of ZnO:N film, X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption near-edge spectroscopy (XANES) measurements have been applied to investigate the local electronic structure and chemical states of nitrogen atoms in ZnO:N films.     

N离子注入富氧ZnO薄膜的p型导电及拉曼特性研究

采用射频磁控溅射法在富氧环境下制备ZnO薄膜, 继而结合N离子注入及热退火实现薄膜的N掺杂及p 型转变, 借助霍尔测试和拉曼光谱研究了N离子注入富氧ZnO薄膜的p型导电及拉曼特性. 结果表明, 在 600 ℃温度下退火120 min可获得性能较优的p-ZnO: N薄膜, 其空穴浓度约为2.527×10¹⁷ cm^-3. N离子注入ZnO引入了三个附加拉曼振动模, 分别位于274.2, 506.7和640.4 cm^-1. 结合电学及拉曼光谱的分析发现, 退火过程中施主缺陷与N受主之间的相互作用对p-ZnO的形成产生重要影响.     

离子束增强沉积制备p型氧化锌薄膜及其机理研究

采用离子束增强沉积方法在Si和SiO₂/Si衬底上制备In-N共掺杂ZnO薄膜(INZO)，溅射靶是用ZnO和2 atm% In₂O₃粉体均匀混合并压制而成，在氩离子溅射ZnO靶的同时，氮、氩混合离子束垂直注入沉积的薄膜.实验结果显示INZO薄膜具有(002)的择优取向，并且为p型导电，电阻率最低为0.9Ωcm.薄膜在氮气、氧气气氛下退火，对薄膜的结构和电学特性与成膜和退火条件的关系进行了分析. 关键词： 氧化锌薄膜 p型掺杂 离子束增强沉积     

Improvement of electrical and optical properties of Ga and N co-doped p-type ZnO thin films with thermal treatment

Ga and N co-doped p-type ZnO thin films were epitaxially grown on sapphire substrate using magnetron sputtering technique. The process of synthesized Ga and N co-doped ZnO films was performed in ambient gas of N₂O. Hall measurement shows a significant improvement of p-type characteristics with rapid thermal annealing (RTA) process in N₂ gas flow, where more N acceptors are activated. The film rapid thermal annealed at 900 °C in N₂ ambient revealed the highest carrier concentration of 9.36 × 10¹⁹ cm⁻³ and lowest resistivity of 1.39 × 10⁻¹ Ω cm. In room and low temperature photoluminescence measurements of the as grown and RTA treated film, donor acceptor pair emission and exciton bound to acceptor recombination at 3.25 and 3.357 eV, respectively, were observed.     

Room-temperature ferromagnetism in N+-implanted ZnO:Mn thin films

Mn–N co-doped ZnO films with wurtzite structure were fabricated by RF magnetron sputtering together with the ion-implantation technique. Then a post-annealing at 650 °C for 10 min in a N₂ atmosphere was performed to activate the implanted N⁺ ions and recover the crystal quality, and a p-type ZnO:Mn–N film with a hole concentration of about 2.1×10¹⁶ cm^?3 was obtained. It is found that the Mn mono-doped ZnO film only exhibits paramagnetic behavior, while after N⁺-implantation, it shows ferromagnetism at 300 K, and the magnetization of the ZnO:Mn–N films can be further enhanced by thermal annealing due to the activation of the N acceptors. Our experimental results confirm that the codoping N acceptors are favorable for ferromagnetic ordering of Mn²⁺ ions in ZnO, which is consistent with the recent theoretical calculations.     

Mn和N共掺ZnO稀磁半导体薄膜的研究

使用对Zn₂N₃:Mn薄膜热氧化的方法成功制备了高含N量的Mn和N共掺ZnO的稀磁半导体薄膜.在没有N离子共掺的情况下,ZnO:Mn薄膜的铁磁性非常微弱;如果进行N离子的共掺杂,就会发现ZnO:Mn薄膜在室温下表现出非常明显的铁磁性,饱和离子磁矩为0.23 μ_B—0.61 μ_B.这说明N的共掺激发了ZnO:Mn薄膜中的室温铁磁性,也就是受主的共掺引起的空穴有利于ZnO中二价Mn离子的铁磁性耦合,这和最近的相关理论研究符合很好. 关键词： 磁性半导体 受主掺杂 空穴媒介的铁磁性     

First-principles study of the formation mechanisms of nitrogen molecule in annealed ZnO

Recently, N₂ molecule was reported to induce localized states in the band gap and trap two holes in ZnO. In this Letter, the detailed mechanism for the formation of N₂ molecule in high temperature annealing process in ZnO was investigated based on density-functional theory. By analyzing the interactions between N-related defects, we found that the nitrogen molecule would form by the binding of two interstitial nitrogen atoms. Interstitial oxygen facilitated the formation of N₂ by kicking out N_O to interstitial site. The formation of nitrogen molecule in ZnO would cause low doping efficiency and degeneration of the p-type in annealing process. Our results could explain the recently reported formation of N₂ molecule in high temperature annealing process in N-doped ZnO. Appropriate annealing conditions were suggested in order to get p-type ZnO.     

p-type conduction in ZnO dual-acceptor-doped with nitrogen and phosphorus

A dual-acceptor doping method was proposed to produce p-type conduction in ZnO. Both nitrogen and phosphorus were used as the p-type doping agents. ZnO:(N, P) films were prepared by spray pyrolysis. The p-type conduction was achieved by thermal annealing at appropriate temperatures (500-700 ^°C) for 20 min in O₂ ambient. The lowest resistivity of , with a hole concentration and Hall mobility of 5.3×10¹⁷ cm⁻³ and 0.94 cm² V ⁻¹ s⁻¹, respectively, was obtained at an optimal annealing temperature of 600 ^°C. The p-type behavior was reproducible and stable. The introduction of nitrogen and phosphorus in ZnO were identified by secondary ion mass spectroscopy.     

p型ZnO薄膜的制备及特性

采用射频磁控溅射在Si片上制备ZnO薄膜，通过离子注入对样品进行N掺杂，在不同温度下进行退火并实现了p型转变.用扫描电子显微镜、X射线衍射和Hall测量对薄膜进行了表征，结果表明薄膜具有良好的表面形貌和高度c轴择优取向，退火后p型ZnO薄膜的最高载流子浓度和最低电阻率分别为1.68×10¹⁶cm^-3和41.5Ω·cm.讨论并分析了退火温度和时间对ZnO薄膜p型转变的影响.     

Electrical properties and Raman scattering investigation of Ag doped ZnO thin films

Ag-doped ZnO thin films were deposited on quartz glass substrates by a radio-frequency (RF) magnetron sputtering technique at room temperature (RT). The influence of Ag doping content on the electrical and Raman scattering properties of ZnO films were systematically investigated by Hall measurement system and Raman scattering spectrum. Two additional local vibrational modes (LVMs) at 230.0 and 394.5 cm^?1 induced by Ag dopant in ZnO:Ag films were observed by Raman analyses at RT, corresponding to Ag atoms located at O sites (LV M_Zn?Ag) and Zn sites (LV M_Ag?O) in ZnO lattice. Moreover, we further studied the effect of donor Ag_O and acceptor Ag_Zn defects on the electrical properties of ZnO:Ag films. The results indicate that O-rich condition is preferred to suppress the formation of Ag_O defects and enhance Ag_Zn defects. The p-type ZnO:Ag film was achieved by properly optimizing the annealing conditions under O-rich condition.     

Preparation of p-type ZnO:(Al, N) by a combination of sol--gel and ion-implantation techniques

We report the preparation of p-type ZnO thin films on (0001) sapphire substrates by a combination of sol--gel and ion-implantation techniques. The results of the Hall-effect measurements carried out at room temperature indicate that the N-implanted ZnO:Al films annealed at 600\du\ have converted to p-type conduction with a hole concentration of $1.6\times10¹⁸cm^-3, a hole mobility of 3.67cm²/V.s and a minimum resistivity of 4.80cm.\Omega$. Ion-beam induced damage recovery has been investigated by x-ray diffraction (XRD), photoluminescence (PL) and optical transmittance measurements. Results show that diffraction peaks and PL intensities are decreased by N ion implantation, but they nearly recover after annealing at 600\du. Our results demonstrate a promising approach to fabricate p-type ZnO at a low cost.     

The effects of thermal annealing in NH3 -ambient on the p-type ZnO films

Thermal annealing in NH₃-ambient was carried out to form p-type ZnO films. The properties were examined by X-ray diffraction (XRD), Hall-effect measurement, photoluminescence (PL), and secondary ion mass spectrometry (SIMS). Electron concentrations in ZnO films were in the range of 10¹⁵–10¹⁷/cm³ with thermal annealing in NH₃-ambient. The activation thermal annealing process was needed at 800 C under N₂-ambient to obtain p-type ZnO. The electrical properties of the p-type ZnO showed a hole concentration of 1.06×10¹⁶/cm³, a mobility of 15.8 cm²/V s, and a resistivity of 40.18 Ω cm. The N-doped ZnO films showed a strong photoluminescence peak at 3.306 eV at 13 K, which is closely related to neutral acceptor bound excitons of the p-type ZnO. The incorporation of nitrogen was confirmed in the SIMS spectra.     

Post-annealing influence on properties of N-In codoped ZnO thin films prepared by ion beam enhanced deposition method

N-In codoped ZnO thin films were prepared by ion beam enhanced deposition method (IBED) and were annealed in nitrogen and oxygen ambient after deposition. The influence of post-annealing on structure, electrical and optical properties of thin films were investigated. As-deposited and all post-annealed samples showed preferential orientation along (0 0 2) plane. Electrical property studies indicated that the as-deposited ZnO film showed p-type with a sheet resistance of 67.5 kΩ. For ZnO films annealed in nitrogen with the annealing temperature increasing from 400 to 800 °C, the conduction type of the ZnO film changed from p-type to n-type. However, for samples annealed in oxygen the resistance increased sharply even at a low annealing temperature of 400 °C and the conduction type did not change. Room temperature PL spectra of samples annealed in N₂ and in O₂ showed UV peak located at 381 and 356 nm, respectively.     

退火温度对N+注入ZnO:Mn薄膜结构及室温铁磁性的影响

采用射频磁控溅射法在石英玻璃衬底上制备了ZnO:Mn薄膜, 结合N⁺ 注入获得Mn-N共掺ZnO薄膜, 进而研究了退火温度对其结构及室温铁磁性的影响. 结果表明, 退火后ZnO:(Mn, N) 薄膜中Mn²⁺和N^3-均处于ZnO晶格位, 没有杂质相生成. 退火温度的升高 有助于修复N⁺注入引起的晶格损伤, 同时也会让N逸出薄膜, 导致受主(N_O)浓度降低. 室温铁磁性存在于ZnO:(Mn, N)薄膜中, 其强弱受N_O浓度的影响, 铁磁性起源可采用束缚磁极化子模型进行解释.     

Investigation of p-type behavior in Ag-doped ZnO thin films by E-beam evaporation

Ag-doped ZnO (ZnO:Ag) thin films were grown on glass substrates by E-beam evaporation technique. The structural, electrical and optical properties of the films were investigated as a function of annealing temperature. The films were subjected to post annealing at different temperatures in the range of 350-650 °C in an air ambient. All the as grown and annealed films at temperature of 350 °C showed p-type conduction. The films lost p-type conduction after post annealing treatment temperature of above 350 °C, suggesting a narrow post annealing temperature window for the fabrication of p-type ZnO:Ag films. ZnO:Ag film annealed at 350 °C revealed lowest resistivity of 7.25 × 10⁻² Ω cm with hole concentration and mobility of 5.09 × 10¹⁹ cm⁻³ and 1.69 cm²/V s, respectively. Observation of a free-to-neutral-acceptor (e,A^o) and donor-acceptor-pair (DAP) emissions in the low temperature photoluminescence measurement confirms p-type conduction in the ZnO:Ag films.     

Structural, optical and electrical properties of Al-N codoped ZnO films by RF-assisted MOCVD method

N-doped ZnO films were produced using N₂ as N source by metal-organic chemical vapor deposition (MOCVD) system which has been improved with radio-frequency (RF)-assisted equipments. The data of secondary ion mass spectroscopy (SIMS) indicate that the concentration of N in N-doped ZnO films is around 5 × 10²⁰ cm⁻³, implying that sufficient incorporation of N into ZnO can be obtained by RF-assisted equipment. On this basis, the structural, optical and electrical properties of Al-N codoped ZnO films were studied. Then, the effect of RF power on crystal quality, surface morphologies, optical properties was analyzed using X-ray diffraction, atomic force microscopy and photo-luminescence methods. The results illustrate that the RF plasma is the key factor for the improvement of crystal quality. Then the observation of A⁰X recombination associated with N_O acceptor in low-temperature PL spectrum proved that some N atoms have occupied the positions of O atoms in ZnO films. Hall measurements shown that p-type ZnO film deposited on quartz glasses was obtained when RF power was 150 W for the Al-N codoped ZnO films, while the resistivity of N-doped ZnO films was rather high. Compared with the Al-doped ZnO film, the obviously increased resistivity of codoped films indicates that the formation of N_O acceptors compensate some donors in ZnO films effectively.     

Structural and electrical properties of nitrogen and aluminum codoped p-type ZnO films

To resolve the problem of p-type doping in ZnO, nitrogen and aluminum (N-Al) codoped ZnO films were prepared by the ultrasonic spray pyrolysis (USP) technique. The structural and electrical properties of N-Al codoped ZnO films were investigated. The results demonstrate that the undoped ZnO films exhibit the preferential orientation of (002) plane, while ZnO films show high orientation of (101) plane after codoping with N and Al. The N-Al codoped ZnO films under optimum conditions show p-type conduction, with a low resistivity of 1.7×10⁻²Ω cm, carrier concentration of 5.09×10¹⁸ cm⁻³ and high Hall mobility of 73.6 cm² V⁻¹ s⁻¹. A conversion from p-type conduction to n-type was observed during the increase of measurement temperature.     

p-Type conduction in phosphorus-doped ZnO thin films by MOCVD and thermal activation of the dopant

Phosphorus-doped p-type ZnO thin films have been realized by metalorganic chemical vapor deposition (MOCVD). The conduction type of ZnO films is greatly dependent on the growth temperature. ZnO films have the lowest resistivity of 11.3 Ωcm and the highest hole concentration of 8.84 × 10¹⁸ cm⁻³ at 420 °C. When the growth temperature is higher than 440 °C, p-type ZnO films cannot be achieved. All the films exhibited p-type conduction after annealing, and the electrical properties were improved comparing with the as-grown samples. Secondary ion mass spectroscopy (SIMS) test proved that phosphorus (P) has been incorporated into ZnO.     

Preparation and characteristics of transparent p-type ZnO film by Al and N co-doping method

Al-N co-doped ZnO films were fabricated by gaseous ammonia annealing at various temperatures. The structure and the electrical properties of Al-N-doped ZnO films strongly depend on the annealing temperature. XRD and SEM analysis indicate that the ZnO films possess a good crystallinity with c-axis orientation, uniform thickness and dense surface. Optical transmission spectra show a high transmittance (∼85%) in the visible region. Hall measurement demonstrates that ZnO films have p-type conduction with high carrier concentration of 8.3 × 10¹⁸ cm⁻³ and low resistivity of 25.0 Ω cm when the annealing temperature is 700 °C. Also the growth process of Al-N co-doped at various temperatures is discussed in detail.     

Photoluminescence properties of thin nitrogen- and phosphorus-doped ZnO films fabricated using pulsed laser deposition

The production of n- and p-type high-quality film structures is a foreground task in tackling the problem of growing the light-emitting p-n junctions based on zinc oxide. The ZnO:N and ZnO:P thin-film samples are produced from ceramic targets using the pulsed laser deposition. Zn₃N₂, MgO, and Zn₃P₂ are introduced in the ZnO ceramic targets for the fabrication of the p-type ZnO films. Gases O₂ and N₂O are used as buffer gases. The thermal annealing of the ZnO films is employed. The resistance and photoluminescence (PL) spectra of the ZnO films are measured prior to and after annealing. The dependence of the ZnO PL peak amplitude and position prior to and after annealing on the level of doping with nitrogen and phosphorus is established. The PL characteristics of the films are studied at cw optical excitation using a He-Cd laser with a radiation wavelength of 325 nm. The PL spectra in the interval 300–700 nm are recorded by an HR4000 Ocean Optics spectrometer in the temperature range 10–400 K. The effect of the conditions for the film deposition on the PL spectra is analyzed. The effect of the N- and P-doping level of the ZnO films on the PL intensity of the films and the position of the PL bands in the UV region is investigated. The short-wavelength (250–400 nm) transmission spectra of the ZnO:P films are measured. The effect of the P-doping level on the band gap of the ZnO films is studied.