Photoluminescence study of hydrogen donors in ZnO

A photoluminescence study of hydrogenated ZnO bulk crystals is presented. Two excitonic recombination lines at 3362.8 and 3360.1 meV are assigned to hydrogen shallow donors. Experimental evidence is presented that the corresponding donor to the line at 3362.8 meV, previously labeled I₄, originates from hydrogen trapped within the oxygen vacancy, H_O. The line at 3360.1 meV was found to be due to hydrogen located at the bond-centered lattice site, H_BC. The corresponding shallow donor has an ionization energy of 53 meV.     

Local structure of isolated positively charged muonium as an analog for the hydrogen ion in p-type GaAs

We determine the local structure of isolated positively charged muonium (Mu+) in heavily doped p-type GaAs based on muon level crossing resonance and zero applied field muon spin depolarization data. These measurements provide the first direct experimental confirmation that Mu+, and by analogy H+, is located within a stretched Ga-As bond. The distances between Mu+ and the nearest neighbor Ga and As atoms are estimated to be 1.83 +/- 0.10 A; and 1.76 +/- 0.10 A, respectively. These results are compared to existing theoretical calculations on the structure of hydrogen in GaAs and additionally provide data on the induced electric field gradients.     

Dynamics and reactivity of positively charged muonium in heavily doped Si:B and comparisons with hydrogen

The detailed dynamics of the positively charged muonium (Mu+) in heavily doped p-type Si:B is reported. Below 200 K, Mu+ is static and isolated, and is located in a stretched Si-Si bond. Above approximately 200 K, Mu+ diffuses incoherently. At temperatures higher than 300 K, the Mu+-B- complex is formed while above 520 K, it starts to dissociate. There is significant enhancement of the diffusion of Mu+ in Si compared to H+ and D+-this is attributed to its smaller mass.     

Muonium dynamics in transparent conducting oxides

The motional and electrical properties of positively charged muonium (Mu⁺)$({\mathrm{Mu}}^{+})$ centers in single crystal β-Ga₂O₃$\mathrm{\beta }\mathrm{-}{\mathrm{Ga}}_2{\mathrm{O}}_3$ are investigated via zero field muon spin relaxation (ZF-MuSR). Below room temperature we find two distinct shallow muonium centers with ionization energies of 7 and 16 meV. Above room temperature, at least three different Mu⁺ signals are resolved; two of these are metastable while the third shows characteristics of a stable ground state. As the temperature is elevated, metastable centers undergo several transitions. We obtain the relevant barrier energies associated with these site-change transitions. By 700 K, most muons occupy the mobile ground state, and an activation energy of about 1.65 eV is inferred for Mu⁺ diffusion from the hop rates obtained for this state.     

Identification of a metastable state of the VZnH2 defect in ZnO

An infrared absorption study of the Zn vacancy passivated by two hydrogen atoms (V_ZnH₂) is reported. The ground state of the defect V_ZnH₂ consists of the inequivalent O–H bonds, which are aligned parallel and perpendicular to the c-axis, respectively. A metastable state of the defect was detected with two equivalent O–H bonds oriented perpendicular to the c-axis (V_ZnH₂^?). V_ZnH₂^? has two local vibration modes at 3329.0 and 3348.4 cm⁻¹ which are the antisymmetric and symmetric combinations of the two O–H stretch modes. The metastable state of the defect is 75±9 meV above the ground state of V_ZnH₂. An activation energy of 0.96±0.12 eV for the transition from metastable to the ground state was determined.     

Charge states of a hydrogen defect (3326 cm line) in ZnO

The hydrogen defect in ZnO that gives rise to a local vibrational mode at 3326 cm⁻¹ is investigated by means of IR absorption. Sub-band gap illumination results in the appearance of a new line at 3358 cm⁻¹ at the expense of the 3326 cm⁻¹ signal. The measurements identify both IR absorption signals as O–H stretch modes of the same defect in different charge states. The effect of the sub-band gap light strongly suggest that this defect has a deep level in the band gap. Additionally, results on the thermal stability of the 3326 cm⁻¹ feature are presented.     

Detection of hydrogen with SnO2-coated ZnO nanorods

SnO₂-coated ZnO nanorods on c-plane sapphire substrates were synthesized by pulsed laser deposition. The thickness of the polycrystalline SnO₂ was ∼10 nm, as determined by high-resolution transmission electron microscopy, while the diameter of the ZnO nanorods was ∼30 nm. The sensitivity of the SnO₂/ZnO structures to hydrogen was tested by depositing Ti/Au Ohmic contacts on a random array of the nanorods and measuring the current at fixed voltage. There was no response to 500 ppm H₂ in N₂ at room temperature, but we obtained a sensitivity of ∼70% at 400 °C. The SnO₂/ZnO structures exhibit drift in their recovery characteristics and for sequential detection of hydrogen, as generally reported for SnO₂ thin film sensors.     

Formation of p-type ZnO film on InP substrate by phosphor doping

ZnO thin film was initially deposited on InP substrate by radio frequency (rf) magnetron sputtering and the diffusion process was performed using the closed ampoule technique where Zn₃P₂ was used as the dopant source. To verify the junction formation of ZnO thin films, the electrical properties were measured, and the effects of Zn₃P₂ diffusion on ZnO thin films were investigated. It is observed that the electrical property of the film is changed from n-type to p-type by dopant diffusion effect. Based on the results, it is confirmed that ZnO thin films can be a potential candidate for ultraviolet (UV) optical devices.     

ESR investigations on hydrogen-induced hyperfine splitting features in ZnO

Low temperature X-band electron spin resonance measurements (ESR) were performed on as-grown and post-hydrogenated zinc oxide (ZnO) single crystals. As-grown ZnO exhibits a single strong line at g=1.957$g=1.957$ that was identified as hydrogen. In contrast, post-hydrogenated ZnO shows a distinctly different ESR spectrum. Besides the intensification of the hydrogen donor line, hydrogenation triggers the observation of additional hyperfine lines. They are attributed to manganese (Mn) impurities probably introduced from the growth process. From the ESR data a Mn concentration of 6×10¹³ cm⁻³ was estimated.     

ZnO2与其热分解所得的ZnO粉末的拉曼光谱研究

利用ZnO2热分解方法制备的ZnO粉末的拉曼光谱,通过分析不同加热温度下所得样品强激光烧蚀后拉曼峰位的差异并对比其他方法所制样品的光谱,指出333 cm-1拉曼峰应当归结为E2(high)和E2(low)的差频,而661 cm-1峰为其二倍频。此外,在量化计算和红外光谱的辅助下,对文献中关于ZnO2粉末在400～500 cm-1之间所观测到的拉曼峰的指认提出了不同看法。     

Self-trapping of positively charged particles in metals

It is shown that the existence of a metastable state in which positrons in metals are “self-trapped” by strong interaction with the lattice gives rise to an anomalous temperature dependence in positron annihilation properties. The “intermediate” temperature variation of the shape of the annihilation photon line discovered by MacKenzieet al. is well accounted for by this mechanism; alternative interpretations in terms of thermal expansion effects may be refuted. This result calls for considerable revision of some of the published monovacancy formation energies obtained from positron annihilation measurements. Approximate criteria for the existence and the metastability of a selftrapped state of positively charged particles in metals are given. It is found that metastable self-trapping may occur for positrons; hydrogen isotopes and positive muons should be self-trapped in configurations that are always stable relative to the Bloch-wave states of these particles.     

Photoluminescence observations of hydrogen incorporation and outdiffusion in ZnO thin films

ZnO thin films were deposited with the addition of H₂ to the reaction gas using the atmospheric-pressure metal organic chemical vapor deposition method. The incorporation and outdiffusion of hydrogen in ZnO films were investigated by comparing the intensity of the hydrogen-related bound-exciton peak (I₄: 3.363 eV) in the photoluminescence spectrum. The intensity of I₄ peak was found to be the strongest in the ZnO film deposited at 680 °C with H₂ present. However, for the ZnO films prepared at the same temperature 680 °C but without H₂ present and at the higher temperature of 900 °C with H₂ present, respectively, the I₄ peak was just a minor shoulder of another bound-exciton peak (I₈: 3.359 eV). The intensity of I₄ peak in the ZnO films deposited with H₂ present was found to decrease with the increasing of annealing temperature. These results suggest that it is difficult for hydrogen to incorporate into ZnO thin films grown at high temperatures even in the hydrogen-present ambient.     

GaN-based light-emitting diode with ZnO nanotexture layer prepared using hydrogen gas

ZnO films were deposited on indium tin oxide (ITO), which formed the transparent conductive layer (TCL) of a GaN-based light-emitting diode (LED), by ultrasonic spraying pyrolysis to increase the light output power. The ZnO nanotexture was formed by treating the as-deposited ZnO films with hydrogen. The root mean square (RMS) roughness increased from 4.47 to 7.89 nm before hydrogen treatment to 10.82-15.81 nm after hydrogen treatment for 20 min. Typical current-voltage (I-V) characteristics of the GaN-based LEDs with a ZnO nanotexture layer have a forward-bias voltage of 3.25 V at an injection current of 20 mA. The light output power of a GaN-based LED with a ZnO nanotexture layer improved to as much as about 27.5% at a forward current of 20 mA.     

Neutral and positively charged excitons in quantum ring

We study theoretically quantized states of the neutral and positively charged exciton complexes confined within a circular narrow ring in the presence of the magnetic field applied along the symmetry axis. We show that in the structural adiabatic limit, when the width of the pattern of the particles pathways within the ring is much smaller than its radius, the wave equations for both complexes are separable and their exact solutions can be found in a form of the Fourier series of one and two variables, respectively. We present results of calculation of the lower energies of complexes as functions of the ring's radius and the magnetic field strength for different values of the electron-to-hole mass ratio. We found that in the molecular adiabatic limit, when this ratio tends to zero and the model describes the corresponding donor complexes, the physical interpretation of the quantum-size effect and the oscillations of energy levels in threading magnetic field revealed for the excitons spectra becomes more transparent.     

Propagation function of channelized positively charged particles

A propagation function for channelized positively charged particles moving in a heaped up oscillator potential is constructed by using the method of coherent states.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 93–97, March, 1982.     

Induced growth of high quality ZnO thin filmsby crystallized amorphous ZnO

This paper reports the induced growth of high quality ZnO thin film by crystallized amorphous ZnO. Firstly amorphous ZnO was prepared by solid-state pyrolytic reaction, then by taking crystallized amorphous ZnO as seeds (buffer layer), ZnO thin films have been grown in diethyene glycol solution of zinc acetate at 80℃. X-ray Diffraction curve indicates that the films were preferentially oriented [001] out-of-plane direction of the ZnO. Atomic force microscopy and scanning electron microscopy were used to evaluate the surface morphology of the ZnO thin film. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. The results indicate that high quality ZnO thin film was obtained.     

Attraction of positively charged particles in highly collisional plasmas

It is shown that the electrostatic interaction potential between a pair of positively charged particles embedded in a highly collisional plasma has a long-range attractive asymptote. The effect is due to continuous plasma absorption on the particles. The relevance of this result to experimental investigations of complex (dusty) plasmas is discussed.