Enling Li

Enhancing the field emission properties of Se-doped GaN nanowires

Pure and Se-doped GaN nanowires (NWs) are synthesized on Pt-coated Si(111) substrates via chemical vapor deposition. The GaN NWs exhibit a uniform density with an average diameter of 20-120 nm. The structure of the NWs is wurtzite hexagonal, and the growth direction is along [0001]. Field emission measurements show that the Se-doped GaN NWs possess a low turn-on field (2.9 V μm(-1)) compared with the pure GaN NWs (7.0 V μm(-1)). In addition, density functional theory calculations indicate that the donor states near the Fermi level are mainly formed through the hybridization between Se 4p and N 2p orbitals and that the Fermi level move towards the vacuum level. Consequently, the work functions of Se-doped GaN NWs are lower than those of pure GaN NWs.

Effect of the VAsVGa complex defect doping on properties of the semi-insulating GaAs

The different position VAsVGa cluster defect doping in semi-insulating (SI) GaAs has been studied by first-principles calculation based on hybrid density functional theory. Our calculated results show that EL6 level is formed due to the VAsVGa complex defect, which is very close to the experimental result. It provides the explanation of the absorption of laser with the wavelength beyond in semi-insulating GaAs. The formation energy of VAsVGa complex defect is found to decrease from surface to interior gradually. The conduction band minima and valence band maxima of GaAs (001) surface with the VAsVGa complex defect are all located at Γ point, and some defect levels are produced in the forbidden band. In contrast, the conduction band minima and valence band maxima of GaAs with the interior VAsVGa complex defect are not located at the same k-point, so it might involve the change of momentum in the electron transition process. The research will help strengthen the understanding of photoelectronic properties a...

First-principles study on stability and photoelectron spectroscopy of GanAs2(n=1–9) clusters

The stability and photoelectron spectroscopy of the Ga(n)As2(n=1-9) clusters have been studied by using first-principles based on density functional theory (DFT). Our calculations reveal that the stabilities of the Ga(n)As2(n=1-9) clusters tend to increase with the increase of the number of total atoms. The calculated second-order difference values of the binding energy show a certain law of even-odd alternation, and the value of the even-numbered clusters is much larger than those of the odd-numbered ones. The energy gap Egap also shows a certain law of even-odd alternation, i.e. the Egap of the even-numbered clusters is much larger than the odd-numbered ones. The Egap of the clusters is between 0.2 eV and 0.6 eV, it will provide a reference for GaAs defect level research. The Ga(n)As2(n=1-9) clusters are potential to detect and emit THz radiation due to their ground-state vibration frequency are in THz range.

GaN nanowire field emitters with the adsorption of Pt nanoparticles

We report Pt NP coated GaN NWs through CVD method and the fabrication of their field emitters. Pt NPs are attached on the top and surfaces of GaN NWs. With the Pt NP coating, it is found that the turn on field is reduced from 3.3 V μm−1 to 2.7 V μm−1 and the work function is decreased from 4.1 eV to 3.22 eV. In addition, DFT calculation results indicate that higher local electron states, which appear around the Fermi level, are mainly formed from N-2p, Pt-6s, and Pt-5d orbital hybridization, and will provide more electrons to the conduction band at a given operating voltage. Consequently, the field emission performance of GaN NWs can be effectively boosted by adsorbed Pt. Moreover, Pt NP coated GaN NWs are promising for electron emission devices, field emission displays and vacuum nano-electronic devices.

Synthesis and excellent field emission properties of three-dimensional branched GaN nanowire homostructures

Three-dimensional branched GaN nanowire homostructures have been synthesized on the Si substrate via a two-step approach by chemical vapor deposition. Structural characterization reveals that the single crystal GaN nanowire trunks have hexagonal wurtzite characteristics and grow along the [0001] direction, while the homoepitaxial single crystal branches grow in a radial direction from the six-sided surfaces of the trunks. The field emission measurements demonstrate that the branched GaN nanowire homostructures have excellent field emission properties, with low turn-on field at 2.35 V/μm, a high field enhancement factor of 2938, and long emission current stability. This indicates that the present branched GaN nanowire homostructures will become valuable for practical field emission applications.

Density functional theory study on defect feature of As Ga Ga As in gallium arsenide

We investigate the defect feature of AsGaGaAs defect in gallium arsenide clusters in detail by using first-principles calculations based on the density functional theory (DFT). Our calculations reveal that the lowest donor level of AsGaGaAs defect on the gallium arsenide crystal surface is 0.85 eV below the conduction band minimum, while the lowest donor level of the AsGaGaAs defect inside the gallium arsenide bulk is 0.83 eV below the bottom of the conduction band, consistent with gallium arsenide EL2 defect level of experimental value (Ec-0.82 eV). This suggests that AsGaGaAs defect is one of the possible gallium arsenide EL2 deep-level defects. Moreover, our results also indicate that the formation energies of internal AsGaGaAs and surface AsGaGaAs defects are predicted to be around 2.36 eV and 5.54 eV, respectively. This implies that formation of AsGaGaAs defect within the crystal is easier than that of surface. Our results offer assistance in discussing the structure of gallium arsenide deep-level defect and its effect on the material.