Narrow Results

Mg-doped GaN films have been successfully prepared on Si(111) substrate by metal-organic chemical vapor deposition (MOCVD). Upon rapid thermal annealing (RTA) treatment, the films showed p-type conductivity with a carrier density of 7.84 cm^-3, a mobility of 5.54 cm²V^-1s^-1, and a resistivity of about 0.144 Ωcm, which were much better than that of the films without rapid thermal annealing (RTA) treatment. It was found that the surface morphology and crystal quality of the obtained p-type GaN films were greatly improved by RTA treatment, while the residual stress and dislocations in these films were decreased.

p-type conductivity and the modulation of bandgap of ZnO are crucial aspects for realization of optoelectronic devices’ applications. The Li and Li-Cu could be suitable doping agents for achieving the p-type conductivity and the modulation of bandgap of ZnO. To this point of view, the Zn${}_{100-x}$Li${}_x$O (x = 0 to 40 at.%) and Zn${}_{100-x-y}$Li${}_x$Cu${}_y$O (fixed, x = 5 at.%, and y = 0.0 to 10 at.%) thin films were prepared on the microscopic glass substrates at a temperature of 350${}^{\circ }$C using cost effective chemical spray pyrolysis (CSP) technique. Field emission scanning electron microscope images show the coexistence of interconnected fibrous and flat grains on the films surface. The grain size changes as function of Li- and Li-Cu concentrations, and at a higher doping granular grains are observed. The successful incorporation of Li and Cu-Li into ZnO crystal is confirmed by X-ray photoelectron spectroscopy (XPS) measurements. The X-ray diffraction (XRD) patterns exhibit hexagonal polycrystalline structure of doped ZnO. However, the crystallinity is deteriorated at higher Li- and Li-Cu doping concentrations. The optical bandgap study exhibits direct transition type and it is red shifted from 3.21 to 2.61 eV and 2.84 to 3.56 eV for Li and Li-Cu doping in ZnO thin films, respectively. The optical conductivity enhances as a result of Li- and Li-Cu doping in ZnO. Therefore, Li- and Li-Cu can effectively be doped to tune bandgap and enhance optical properties of ZnO for electronic and optoelectronic device applications.

P-type GaN was successfully achieved by vertically implanting positive monovalent cations of oxygen (O${}^{+}$) into undoped (native n-type with an electron concentration of $8.7\times 10^{16}$cm${}^{-3}$) (0001) monocrystalline GaN. This implantation was carried out with an energy of 200keV and a dose of $5\times 5\times 10^{15}$ ions/cm². In the absence of subsequent rapid thermal annealing (RTA) or when exposed to RTA at 950°C for 10s in a nitrogen ambient environment, temperature-dependent Hall measurements in a vacuum consistently indicated stable p-type conductivity. For the sample that underwent subsequent RTA, the room-temperature Hall hole concentration measured $8.03\times 10^{17}$cm${}^{-3}$, the Hall resistivity was 0.44$\mathrm{\Omega }$⋅cm, the Hall hole mobility reached 17.81cm²⋅V${}^{-1}$⋅s${}^{-1}$, and the acceptor ionization energy was determined to be 0.08eV. The doping efficiency was calculated at 5.5%. O${}^{+}$ ions effectively serve as acceptors, whether annealed or not. The p-type conductivity induced by O${}^{+}$ implantation in GaN is notably advantageous and holds practical significance for the ongoing development of future device technology.

Using first-principles calculations, we systematically investigate the defect physics in topological insulator AuTlS₂. An optimal growth condition is explicitly proposed to guide for the experimental synthesis. The stabilities of various native point defects under different growth conditions and different carrier environments are studied in detail. We show that the p-type conductivity is strongly preferred in AuTlS₂, and the band gap can be engineered by the control of intrinsic defects. Our results demonstrate that AuTlS₂ is an ideal p-type topological insulator which can be easily integrated with traditional semiconductor.

Study of corundum-type chromium oxide ($\alpha$-Cr₂O₃) crystal doped with the nitrogen and magnesium impurities has been carried out through the use of first-principles calculations based on the density functional theory (DFT) and generalized gradient approximation (GGA). Three cases corresponding different impurity–impurity distances have been considered. Structural, electronic and magnetic properties have been studied for all co-doping cases. The $p$-type electrical conductivity was found when distance between the Mg and N atoms is equal to 4.10 Å. The results obtained are consistent with the available experimental data.

Delafossite CuFeO${}_{2-x}$ thin films were fabricated on quartz substrate using radio-frequency sputtering deposition under low O₂ flow ratios from 9% to 0% at room temperature. The as-deposited films were in amorphous phase and crystallized into rhombohedral 3R (R3m) delafossite structure after post annealing at 900${}^{\circ }$C for 2 h in flowing N₂ atmosphere. SEM images showed that the films were composed of nano-sized crystallized grains, thin film composed of smoother surface and higher oxygen content was obtained under higher oxygen percentage in sputtering gas. The optical transmission spectra of these films were studied in the wavelength range 200–1500 nm and the results revealed a narrowing trend of direct bandgap from 3.09 eV to 2.98 eV with the decrease of oxygen flow ratio during deposition. All of the post-annealed CuFeO${}_{2-x}$ thin films exhibited p-type conductivity and linear ohmic contact feature with Cu electrodes. The carrier concentration of thin films increased from $2.8\times 10^{17}{\mathrm{\text{cm}}}^{-3}$ to $9.2\times 10^{19}{\mathrm{\text{cm}}}^{-3}$ whereas the carrier mobility decreased from $9.74{\mathrm{\text{cm}}}^2\cdot {\mathrm{\text{V}}}^{-1}\cdot {\mathrm{\text{s}}}^{-1}$ to $0.035{\mathrm{\text{cm}}}^2\cdot {\mathrm{\text{V}}}^{-1}\cdot {\mathrm{\text{s}}}^{-1}$ as the oxygen flow ratio reduced from 9% to 0%. The ability of controlling compound composition enables tuning of carrier concentration and mobility in CuFeO${}_{2-x}$ and offering essential technical basis in engineering photoelectronic devices.

The electronic and magnetic properties of (Cu, N) co-doped zinc oxide (ZnO) with different Cu:N ratios of 1:2, 1:1 and 2:1 have been studied based on the density functional theory. Mono-doping of Cu or N into ZnO keeps its direct band gap semiconductor nature and exhibits its $p$-type conduction, half-metallic properties for valance band merging below the acceptor levels in a spin direction. However, co-doping of Cu and N into ZnO greatly enhances its conductivity of the system and makes it exhibit metallic properties, the metallic properties become more obvious as the ratio of Cu:N increases from 1:2 to 2:1. Furthermore, co-doping of Cu and N into ZnO can increase magnetic moment for the interaction among Cu $3d$, N $2p$ and O $2p$. ZnO:2Cu–N model is the most stable model in thermodynamics but it shows anti-ferromagnetism (FM) while ZnO:Cu–N system can achieve room-temperature FM, so Cu:N ratios of 1:1 may achieve better electronic and magnetic properties by comprehensive comparison.