The potential use of combined e
-γ vs γ-γ Perturbed Angular Correlations (PAC) experiments as a possible alternative to study electronic properties of materials and/or samples where Hall effect ...measurements are difficult to perform due to low-quality ohmic contacts is here demonstrated using Si- and Zn-doped GaN samples as a showcase example. To do so, the lattice site of implanted
Hf/
Ta and the recombination of Ta ionized and excited electronic states were studied as a function of temperature and sample doping in GaN. By combining the γ-γ and e
-γ PAC results with Density Functional Theory simulations, it was possible to assign a single stable site with a double-donor character for Ta in GaN. A metastable charge state was also identified at particular temperatures using e
-γ PAC. A thermally activated process was observed for the electronic recombination at high temperatures with activation energies of 15(2) meV and 12(1) meV for the Si- and Zn-doped samples, respectively, and attributed to Si shallow donors present in both samples. A reduced number of available electrons was observed in the Zn-doped sample due to donor compensation by the Zn acceptors. At low temperatures, it is suggested that the recombination process occurs via Variable Range Hopping. The doping characteristics of both samples were successfully distinguished.
In the field of Perturbed Angular Correlation (PAC) measurements Avalanche Photo Diodes (APD) are rarely used, despite their favourable properties for fast counting purposes at low energies. This ...work demonstrates their application in combination with a simple and cheap custom build voltage sensitive preamplifier module. Using the PAC nuclei 83Rb(83Kr) and 83mKr(83Kr), the time resolution of the set-up is analysed and the feasibility of precise timing measurements is shown.
► Implantation damage in ZnO is removed during 20
min annealing at 1000
°C. ► Implanted rare earth (RE) ions diffuse towards the surface during this annealing. ► Rapid thermal annealing suppresses ...diffusion but RE are driven from the substitutional to random interstitial sites. ► Clusters of RE with defects and/or other RE are probably responsible for the failure of optical activation of implanted RE in ZnO.
Zinc oxide epilayers grown by metal organic vapour phase epitaxy on (0
0
0
1) sapphire substrates were doped with
Praseodymium and
Europium by ion implantation. The as-implanted samples were either annealed in air for 20
min in a tube furnace or rapid thermal annealing (RTA) was performed, for 2
min, in a nitrogen atmosphere. The samples were characterized by Rutherford Backscattering Spectrometry/Channelling and photoluminescence. The presented results indicate that in the as-implanted samples the majority of the rare earth (RE) ions are incorporated into substitutional Zn-sites. Furnace annealing at 1000
°C recovers the crystal quality of the samples but leads to an out-diffusion of the RE. RTA suppresses diffusion but lattice damage is not fully recovered at 1000
°C. More importantly, during RTA the RE ions are driven from the substitutional site and are now found mainly on random interstitial sites and no optical activation could be achieved.
Rare earth (RE) ions implanted GaN films were studied by optical spectroscopy and RBS techniques. Sharp emission lines due to intra-4f
n
shell transitions can be observed even at room temperature for ...the Eu
3+ and Pr
3+. The photoluminescence spectra recorded by the above band gap excitation reveal dominant transitions due to the
5D
0→
7F
1,2,3 lines at 6004, 6211 and 6632
Å for the Eu
3+ and
3P
0,1→
3F
2,3 at 6450 and 6518
Å, respectively, for the Pr
3+. We report on the temperature dependence of the intra-ionic emissions as well as on the lattice site location of the RE detailed angular scans through the 〈0
0
0
1〉 and
〈1
0
1
̄
1〉
axial directions; which indicates that for Pr, complete substitutionality on the Ga sites was achieved while for Eu a Ga displaced site was found.
In the field of Perturbed Angular Correlation (PAC) measurements Avalanche Photo Diodes (APD) are rarely used, despite their favourable properties for fast counting purposes at low energies. This ...work demonstrates their application in combination with a simple and cheap custom build voltage sensitive preamplifier module. Using the PAC nuclei
83
Rb(
83
Kr) and
83m
Kr(
83
Kr), the time resolution of the set-up is analysed and the feasibility of precise timing measurements is shown.
The versatility of perturbed angular correlations (PAC) in the study of nanostructures and thin films is demonstrated, namely for the specific cases of ZnO/CdxZn1−xO thin films and Ga2O3 powder ...pellets and nanowires, examples of transparent conductive oxides. PAC measurements as a function of annealing temperature were performed after implantation of 111mCd/111Cd (T1/2 = 48 min) and later compared to density functional theory simulations. For ZnO, the substitution of Cd probes at Zn sites was observed, as well as the formation of a probe‐defect complex. The ternary CdxZn1−xO (x = 0.16) showed good macroscopic crystal quality but revealed some clustering of local defects around the probe Cd atoms, which could not be annealed. In the Ga2O3 samples, the substitution of the Cd probes in the octahedral Ga‐site was observed, demonstrating the potential of ion‐implantation for the doping of nanowires.
The influence of external uniaxial stress on the different indium-donor complexes in silicon has been studied using the perturbed
γ
–
γ
angular correlation (PAC) method. Such effect of an applied ...stress is detected by means of the probe atoms situated at different complexes in the sample. The current results showed that the responses of the probes in an extrinsic silicon samples are found to be dissimilar for the same value of stress. Such change in the local environments of the probe atoms could be associated with the various strain field created by the implantations of varied size of impurities. The phosphorous implantation in silicon has even lead to the complete absence of observable effect of the applied stress suggesting significant lose of the elasticity of the sample.
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