The electron density distribution of wurtzite-type gallium nitride (-GaN) was obtained by the Maximum Entropy Method (MEM) using the Synchrotron Radiation powder data. Contribution of the very minor zinc blende-type phase (z-GaN) to the observed powder data was eliminated by the modified Rietveld method. In the obtained MEM electron density distribution map, there are two kinds of Ga-N covalent bonds. The electron density at the saddle point of Ga-N bond parallel to [001] axis is 0.5 [e/Angstrom(3)]. On the other hand, that of the other three equivalent Ga-N bonds are 0.8[e/Angstrom(3)]. Furthermore, it is found that the electron distribution of N atom shows asymmetric distortion. These features suggest asymmetric thermal vibrations of N atom which are restricted by Ga-N bonds.

Bulk single crystals of GaN were used for epitaxial growth of GaN films by molecular beam epitaxy. Low temperature photoluminescence yields much higher intensity emission in the near bandedge region for epitaxial films with respect to the situation in bulk crystals. Character of this luminescence changes also. Dominant band-to-band transitions in the bulk crystals are exchanged by bound exciton and/or donor-acceptor pair transitions observed in the epitaxial layers. We will compare the obtained results with the available data on the homoepitaxial samples grown by metalorganic chemical vapor deposition method and discuss the importance of establishing the basic information on energetic positions of excitonic transitions in stress free samples.

The pressure effect on the rate of the Discontinuous Ordering reaction in the Fe - 50% at. Co system was studied. The distribution function for the activation volume for the grain boundary self-diffusion as a function of grain boundary structure was determined. The activation volumes range from 0.15 to 0.38 in atomic volume units. The result was interpreted in terms of a vacancy mechanism of GB diffusion with a varying degree of vacancy relaxation depending on the grain boundary structure.

Redistribution of oxygen atoms and creation of defects in oxygen - implanted silicon (Si:O-2 oxygen dose up to 6x10(17)cm(-2), energy up to 200 keV), subjected to treatment at high temperature, HT (up to 1570 K) - high hydrostatic pressure, HP (up to 1.5 GPa), are investigated.The treatment of Si:O at less than or equal to 1230 K - 1 GPa does not affect markedly the oxygen distribution profiles; at greater than or equal to 1400 K it results in the HP - dependent decrease of oxygen content and in the change of oxygen profile shape while creation of dislocations is suppressed. The treatment induced effects in Si:O are related to HP - stimulated oxygen clustering (creation of sub - stoichiometric SiO2-x), to decreased oxygen diffusion rate and to altered misfit at the SiO2-x / Si matrix boundary.

Effect of hydrostatic pressure up to 1.2 GPa on oxygen-implanted silicon, Si:O (O+ dose, D, within the 6 x 10(17)-2 x 10(18) cm(-2) range), treated at 1230-1570 K, was investigated by X-ray, transmission electron microscopy and photoluminescence methods. The pressure treatment affects oxygen precipitation and defect creation, especially in low oxygen dose implanted Si:O (D = 6 x 10(17) cm(-2)). Such investigation helps in understanding the stress related phenomena in Si wafers with buried insulating layer.

Effect of annealing at up to 1400 K under argon pressure up to 1.2 GPa on hydrogen-plasma-etched and hydrogen-implanted Czochralski or floating-zone-grown single-crystalline-silicon (FZ), were investigated by secondary ions mass spectrometry (SIMS), X-ray, transmission electron microscopy (TEM), electrical, infrared and photoluminescence (PL) methods. External stress during annealing of hydrogen-containing Si results in suppression of hydrogen out-diffusion, but in its pronounced diffusion into the sample depth. The result is also stress-stimulated creation of small bubbles, thermal donors and crystallographic defects and prevention of sample splitting.

Influence of hydrostatic pressure (HP) on the evolution of Si-O bond states during annealing (HT) in implanted (dose 10(15) - 6 x 10(17) at/cm(2)) Si:O structures was studied by monitoring the features of absorption band associated with Si-O-Si asymmetric stretching mode and defect-related photo luminescence (PL) measurements in the near infrared region. It has been stated that high pressure (HP) treatment significantly changes the defect structure in implanted layer at T greater than or equal to 1130 degreesC, resulting in the shift of asymmetric stretching vibration mode associated with Si-O bonds towards lower frequencies. Stimulation role of hydrostatic pressure in the generation of Si-O bonds in Si:O structures implanted with low doses of oxygen atoms (10(15) -10(16) at/cm(2)) and treated at lower temperatures was found.

We have investigated the high-pressure high-temperature annealing of Mg/P-implanted GaN films using visible and ultraviolet (UV) micro-Raman spectroscopy. The results illustrate the use of Raman spectroscopy to monitor processing of GaN where fast feedback is required. The structural quality and the stress in ion-implanted GaN films was monitored in a 40nm-thin surface layer of the sample as well as averaged over the sample layer thickness. We find the nearly full recovery of the crystalline quality of ion-implanted GaN films after annealing at 1400-1500°C under nitrogen overpressures of 1.5GPa. No significant degradation effects occurred in the GaN surface layer during the annealing. The high nitrogen overpressures proved very effective in preventing the nitrogen out-diffusion from the GaN surface. Stress introduced during the annealing was monitored. Raman spectra of ion-implanted GaN films were investigated at different temperatures and excitation wavelengths to study the GaN phonon density of states.

The effect of external stress exerted by enhanced (up to 1.5 GPa) hydrostatic pressure (HP) of argon ambient during annealing of oxygen-implanted silicon (oxygen dose ≤1×1017 cm−2) up to 1470 K on oxygen agglomeration has been investigated by secondary ion mass spectrometry, transmission electron microscopy, and X-ray and photoluminescence methods. HP treatment results in oxygen distribution shift and massive creation of oxygen precipitates, whereas creation of dislocations is strongly suppressed.

Light emission in thin films (SiO2, SiO2:Si and Si3N4) on a single crystalline silicon surface has been investigated after treatment at enhanced argon pressure, HP. Pronounced effect of HP up to 1.5 GPa during annealing up to 1550 K on photoluminescence, PL, of the SiO2, SiO2:Si and Si3N4 films of 0.1 - 1.2 mum thickness has been stated. The pressure - temperature treatment results in development and enhancement of ultraviolet and visible PL at about 290 - 320, 360, 460, 600 and 680 nm, related to stress induced creation of PL active silicon nanoclusters and other oxygen deficient defects.

Visible and ultraviolet micro-Raman scattering was employed to monitor the high-pressure high-temperature annealing of Mg/P-implanted GaN films. The results illustrate the use of Raman scattering to monitor processing of GaN where fast feedback is required. Temperatures up to 1500 °C with nitrogen overpressures of 1–1.5 GPa were used during the annealing. The crystalline quality, the strain, and the free carrier concentration in the ion-implanted GaN films was monitored, averaged over the layer thickness and in a 40-nm-thin surface layer of the sample. Annealing temperatures of 1400–1500 °C were found to result in the nearly full recovery of the crystalline quality of ion-implanted GaN. No significant surface degradation occurred during the annealing. High nitrogen overpressures proved very effective in preventing the nitrogen out-diffusion from the GaN surface at high temperatures. Strain was introduced during the annealing. Changes in the free carrier concentration were studied.

The kinetics of growth of the Cd21Ni5 intermetallic phase in two-layer Cd-Ni samples has been studied at hydrostatic pressures 0.05–0.9 GPa and at temperatures 200–280°C. Arrhenius equations for both interdiffusion through the growing phase layer and the interfacial reaction have been obtained for different pressures. The activation volumes have been found to be 0.9V0 for interdiffusion and 1.6V0 for interfacial reaction, where V_0 ≈ 1.8 × 10-29m3 is the average volume per atom in the Cd21Ni5 lattice. Atomistic mechanisms of intermetallic growth are discussed.

Effect of annealing (up to 1550 K) under enhanced argon pressure (up to 1.5 GPa) on hydrogen and oxygen - implanted Czochralski or FZ silicon (Si:H and Si:O) was investigated by SIMS, X-ray, photoluminescence (PL), electrical and related methods. External stress during annealing of Si:H results in suppression of hydrogen out - diffusion and in its pronounced diffusion into sample depth, in stress - stimulated creation of small defects/thermal donors, as well as in PL at about 0.8 eV. Stress - annealed Si:O samples indicate strong dependence of X-ray diffuse scattering and of dislocation - related PL on the pressure of ambient gas.

Results on introduction of magnesium to GaN by three methods are presented. They consists of (i) high pressure growth of bulk, single crystals of GaN from Ga+Mg melt, (ii) diffusion of Mg to bulk GaN and to layers of GaN/Al2O3 at high temperatures and high pressures and (iii) implantation of Mg to bulk, single crystals and to layers of GaN/Al2O3 and subsequent high-pressure annealing. Applied pressure is in the range of 10–15 kbar and temperatures between 1200–1500°C. The growth of bulk, highly Mg doped crystals leads to the semi-insulating material with the characteristic blue photoluminescence band at about 3 eV. High pressure annealing of bulk crystals as well as GaN/Al2O3 layers in (N2 +Mg) atmosphere leads to the increase in the Mg incorporation with the highest diffusivity observed for GaN/Al2O3 layers. The performed experiments give an evidence of the importance of the defect (dislocations) in diffusion of Mg in the GaN semiconductor. Moreover, incorporation of Mg impurity appears to be higher on (00.1) Ga-face of the wurtzite GaN crystals than on the (00.−1) N-face. We demonstrate also a strong enhancement of the blue-photoluminescence intensity in high pressure annealed GaN/Al2O3 layers (N2+Mg atmosphere) and Mg-implanted and high pressure annealed GaN crystals and layers.

Effect of annealing at (720-1000) K/1400 K under argon pressure up to 1.2×109 Pa on photoluminescence related to defects created in oxygen-containing (Czochralski grown or oxygen-implanted) silicon was investigated by optical, synchrotron, X-ray and related methods. For the samples pressure-treated at 1400 K the intensity of dislocation-related photoluminescence lines was found to be reduced in comparison to that for the samples annealed at ambient pressure. An increase of photoluminescence intensity at 0.97–1.04 eV, a reduction of X-ray diffuse scattering intensity as well as creation of large (up to 15 μm) oxygen-related defects were stated for the samples annealed at 1400 K under high pressure. An explanation of observed phenomena is proposed.

The effect of pressure and temperature on the distribution function for the activation energy and activation volume of the discontinuous precipitation reaction in a Cu - 7.5 at.% In alloy has been studied. For each pressure and temperature the distribution functions for the activation energy and activation volume for the grain boundary (GB) diffusivity were determined. It was found that the average activation volume increases from 0.75 to 1.5 atomic volumes, when the temperature is increased from 310 to 370°C. At each temperature the activation energy and activation volume vary within 15% to 30% around the average.

GaN is the key material for blue and ultraviolet optoelectronics. It is a strongly bonded wurztite structure semiconductor with the direct energy gap 3.5 eV. Due to strong bonding, the diffusion processes require high temperatures, above 1300 K. However at this temperature range at ambient pressure, GaN becomes unstable and dissociates into Ga and N-2. Therefore high pressure of N-2 is required to study the diffusion and other annealing related processes. We studied annealing of bulk GaN nitride single crystals grown under high pressure and also annealing of homo- and heteroepitaxial GaN layers grown by MOCVD technique. Annealing at temperatures above 1300 K influences strongly the structural and optical properties of GaN crystals and layers. At this temperature diffusion of the Mg and Zn accepters have been observed. In spite of very interesting experimental observations the understanding of microscopic mechanisms of these processes is limited. (C) 1999 Elsevier Science B.V. All rights reserved.

The effect of annealing at argon pressure, HP, up to 1.5 GPa on photoluminescence, PL, of oxy gen-containing silicon (of Czochralski grown, Ct-Si, and of oxygen implanted, Si:O) and of thermally - grown SiO2 films was investigated. Pressure-annealing of Cz-Si and Si: O at 720 to 1400 K affects the intensity of dislocation-related PL lines in the infrared, which follows from HP effect on oxygen precipitation in silicon and Si:O. For the first time visible/ultraviolet PL of the SiO2 surface film was detected after subjecting it to pressure treatment at (1400 to 1550) K, (0.9 to 1.5) GPa.

The kinetics of the gamma-phases Cd21Ni5 and Cu5Zn8 growth during interdiffusion in two-layer Cd-Ni and Zn-Cu samples has been studied under hydrostatic argon pressure 0.05 - 0.9 GPa in the temperature range 200 - 280 degrees C. Kinetics of the intermetallic growth occurs due to diffusion of fast components Cd and Zn through the growing phase layer, in diffusional-kinetic regime for Cd21Ni5 and diffusion regime for Cu5Zn8. Arrhenius equations for Cd diffusion in Cd21Ni5, Zn diffusion in Cu5Zn8, and chemical reaction at the Cd21Ni5-Ni interface have been obtained at 0.05 and 0.9 GPa. Diffusion activation volumes have been estimated as 0.9V(0) and 0.6V(0) for Cd and Zn respectively (V-0 is the average volume per atom in the compounds), and the activation volume for reaction has been found to be 1.6V(0). Diffusion mechanisms are discussed.