Shunming Zhu

Suppression of compensation from nitrogen and carbon related defects for p-type N-doped ZnO

In this letter, the authors performed a comprehensive study on suppression mechanism of compensation from nitrogen and carbon related complex defects in N-doped ZnO grown by metal-organic chemical vapor deposition. The chemical bonding information of donorlike substitutional complex defects, (NN)O and (NC)O, were restrained with low N/O ratio, leading to the conduction type conversion. High epitaxial temperature has more suppressing effect on the formation of desired acceptor NO than that of (NC)O, as evident by the decreasing hole concentration. Upon utilization of such suppression effect, this study provides a promising route to realize p-type ZnO.

Tellurium assisted realization of p-type N-doped ZnO

In this paper, the authors demonstrate an effective pathway to enhance the p-type conduction in N-doped ZnO through codoping method with tellurium during metal-organic chemical vapor deposition process. Tellurium may act as a surfactant in reducing the formation energy of the NO acceptors and thus to enhance the incorporation efficiency of nitrogen. In addition, this codoping method shows a significant effect in suppressing the formation of donorlike carbon related complexes. The increased hole carrier concentration exhibits strong evidence to the enhancement of dopant solubility, and the Te–N codoping method provides an efficient technique for realizing p-type ZnO.

Carbon clusters in N-doped ZnO by metal-organic chemical vapor deposition

We employed transmission electron microscopy and Raman spectra to investigate the behavior of impurity carbon usually unintentionally introduced in N-doped ZnO by metal-organic chemical vapor deposition. Unintentional doped carbon may form graphite clusters along grain boundaries resulting in n-type domains and possibly be a big obstacle for the realization of p-type conductivity. The enhanced desorption rate of hydrocarbon radicals by high temperature and oxygen atom will significantly suppress carbon incorporation rate. The results provide understandings of the formation mechanism of carbon clusters and help us find some available routines to minimize carbon impurity for realization of p-type N-doped ZnO.

Influence of thermally diffused aluminum atoms from sapphire substrate on the properties of ZnO epilayers grown by metal-organic chemical vapor deposition

In this study, the authors investigate the evolution of the structural and electrical properties of ZnO epilayers grown by the metal-organic chemical vapor deposition method on c-sapphire substrates. The inserting of a low-temperature ZnO buffer layer not only significantly improves the structural quality of the high-temperature (HT)-grown ZnO epilayer on a sapphire substrate but also results in high background electron concentration in it from the Hall-effect measurement. After subtracting the conductive contribution from a thin degenerated layer mostly formed between the buffer layer and the substrate based on the two-layer model, the deduced electron-carrier concentration is still in the order of 1018 cm−3, which is much larger than the 1016 cm−3 obtained from capacitance-voltage measurement near the top surface. This indicates that a much thicker layer with high carrier concentration should be formed in the HT-grown ZnO epilayer, which is significantly different from that observed in GaN epitaxy, wher...

Two-dimensional electron gas related emissions in ZnMgO/ZnO heterostructures

Research is supported by the State Key Program for Basic Research of China under Grant No. 2011CB302003 and National Natural Science Foundation of China (Nos. 61025020 and 60990312).

Influence of unintentional doped carbon on growth and properties of N-doped ZnO films

The evolution of optical and electrical properties induced by rapid thermal annealing is studied on nitrogen-doped ZnO samples grown by metal-organic chemical vapor deposition (MOCVD). Correspondingly, in the Raman spectra carbon cluster related D and G modes have been observed to increase with annealing temperature. The increase in the intensity ratio of D and G modes indicates growing of carbon clusters, revealing an interesting change in unintentional doped carbon, which is a popular impurity in MOCVD grown N-doped ZnO. Substitutional or interstitial carbons in the grains may migrate to grain boundaries to incorporate with some existing carbon clusters to form larger ones. Accordingly, zinc vacancies will then be easily formed as annealing temperature increased, resulting in eminent green band emission at room temperature photoluminescence. The band edge emissions also show significant changes with several shoulders observed by thermal annealing, which can be ascribed to acceptor or donor related emiss...

Annealing in tellurium-nitrogen co-doped ZnO films: The roles of intrinsic zinc defects

In this article, the authors have conducted an extensive investigation on the roles of intrinsic zinc defects by annealing of a batch of Te-N co-doped ZnO films. The formation and annihilation of Zn interstitial (Zni) clusters have been found in samples with different annealing temperatures. Electrical and Raman measurements have shown that the Zni clusters are a significant compensation source to holes, and the Te co-doping has a notable effect on suppressing the Zni clusters. Meanwhile, shallow acceptors have been identified in photoluminescence spectra. The NO-Zn-Te complex, zinc vacancy (VZn)-NO complex, and VZn clusters are thought to be the candidates as the shallow acceptors. The evolution of shallow acceptors upon annealing temperature have been also studied. The clustering of VZn at high annealing temperature is proposed to be a possible candidate as a stable acceptor in ZnO.

Influence of oxygen precursors and annealing on Fe3O4 films grown on GaN templates by metal organic chemical vapor deposition

O2 and N2O, popular oxygen precursors for oxide films growth, have been employed to grow Fe3O4 films on GaN templates via metal organic chemical vapor deposition (MOCVD). A (111)-oriented Fe3O4 film was preferably deposited when N2O was used as O precursor, while a Fe2O3 film was grown with O2 as O precursor. A high-temperature annealing has caused a phase transition from α-Fe2O3 to Fe3O4 for O2 case, but no obvious change occurred on the Fe3O4 film for N2O case. Thinner Fe3O4 layer was then grown on a GaN template with N2O as O precursor to form ferromagnetic material (FM)/nonmagnetic material (NM) heterostructure, which is critical for the realization of spin injection in GaN based wide band gap semiconductors. The Ga diffusion from the GaN template to the Fe3O4 layer has been controlled at a rather low level possibly due to the employed low-temperature growth, leading to a high-quality FM/NM heterostructure. An obvious enhancement on the Ga diffusion has been observed upon subsequent annealing for the ...

Mutually beneficial doping of tellurium and nitrogen in ZnO films grown by metal-organic chemical vapor deposition

The advantages of tellurium-nitrogen (Te-N) codoping are investigated in ZnO films grown by metal-organic chemical vapor deposition. Te incorporation gives aid in enhancing the N solubility by lowering its formation energy while N addition helps to stabilize the substituted Te on O sites with the phase-segregated ZnTe crystallites suppressed by forming the N-Zn-Te structures in the N-doped ZnTexO1−x. Carbon related impurities, commonly existing in N-doped ZnO and acting as compensating centers for holes, are fully eliminated by the Te-N codoping. The codoping technique also lowers the energy level of the NO acceptors and leads to realizing N-doped ZnTexO1−x films with holes as major carriers.

Mn incorporation induced changes on structure and properties of N-doped ZnO

The influences of Mn doping on the electrical and optical properties of the Zn1−xMnxO:N films have been investigated. Mn incorporation occupying on the Zn site has led the lattice constants and the bandgap of the films increased with the structural quality deteriorated. The electrical properties have been found to change significantly with the content of Mn in the films, due to the changes in the amount of the NO acceptors and CN compensation centers formed in the films by Mn incorporation as revealed by x-ray photoelectron spectrometry measurements. The chemical states of Mn have been identified as Mn2+ and Mn4+, corresponding to Mn occupying on the Zn site and MnO2 second phase, respectively. The conductive type and the Mn2+ content of the films show a strong effect on the magnetic properties, which can be explained from the theoretical predication on the Mn 3d and N 2p ferromagnetic (hole) coupling on the ferromagnetism. However, uncompensated spins from nonuniform distribution of Mn atoms in ZnO may a...