R. Magerle

Experimental evidence of the self-compensation mechanism in CdS

Abstract Microscopic origin of full electrical compensation of donor doped CdS was analyzed with perturbed angular correlation and Hall-effect measurements. Single crystals were implanted with radioactive 111 In and stable 115 In ions. Total In concentration ranged from 1016 to 1020/cm3. A strong correlation was observed between electrical self-compensation and the formation of (InCd–VCd) pairs (A centers) as a result of thermal annealings. It is shown that the presence of In donors during thermal treatment under the S pressure provokes spontaneous formation of (doubly) ionized cation vacancies [VCd]. During cooling, these vacancies form pairs with In donors (A center), which compensate the rest of the donors, leading to highly resistive material. The experiments presented provide direct evidence for self-compensation: doped crystals spontaneously create just a matching concentration of native point defects needed to compensate foreign doping atoms electrically. This holds for over four orders of magnitude of In concentrations.

Annealing of Cd-implanted GaAs: Defect removal, lattice site occupation and electrical activation

A systematic investigation of the behavior of Cd‐implanted GaAs after rapid thermal annealing is presented. The use of various experimental techniques gives a detailed picture regarding the annealing process in the low‐dose regime (1012 and 1013 cm−2) on a microscopic as well as on a macroscopic scale. Perturbed angular correlation experiments, using the radioactive probe 111mCd, yield information on the immediate environment of the Cd implant on an atomic scale. Rutherford backscattering channeling and photoluminescence spectroscopy give complementary information concerning the overall damage level in the implanted layer, Hall measurements are used to determine the degree of electrical activation of the implanted Cd acceptors. The outdiffusion of the implanted radioactive Cd atoms is also investigated. The removal of defects in the next‐nearest neighborhood of the Cd atoms takes place after annealing at 700 K and is accompanied by a general recovering of the crystal lattice. Between 600 and 900 K more di...

Cd‐H pairs in GaAs: Identification and stability

The Cd‐H complex in 111mCd‐doped GaAs implanted with low‐energy (150–400 eV) hydrogen atoms is identified and studied by perturbed angular correlation spectroscopy using radioactive 111mCd as a probe. By measuring the fraction of Cd‐H pairs in an isochronal annealing experiment, the stability of the pairs is deduced yielding a dissociation energy of ED=1.35(10) eV. After 111mCd implantation but preceding the H loading, the GaAs samples have to be annealed at temperatures exceeding 900 K in order to form Cd‐H pairs. These temperatures are in agreement with the temperature range required for electrical activation of Cd implants, suggesting that a Coulombic interaction is responsible for the formation of Cd‐H pairs in GaAs.

First Microscopic Observation of Cadmium-Hydrogen Pairs in GaN

The formation and properties of acceptor-hydrogen pairs in GaN have been studied using radioactive {sup 111m}Cd acceptors and the perturbed {gamma}{gamma} angular correlation spectroscopy (PAC). After H-loading by low energy implantation (100 eV) at temperatures between 295K and 473 K, the formation of two Cd-H complexes involving about 30% of the Cd-acceptors is observed. The complexes have been identified as single hydrogen atoms bound to the Cd acceptor in two different configurations. The dissociation enthalpies of these configurations have been determined as 1.1(1) eV and 1.8(1) eV, respectively.

DEFECTS IN CDS - IN DETECTED BY PERTURBED ANGULAR-CORRELATION SPECTROSCOPY (PAC)

Abstract The local lattice environment of the donor In in CdS is investigated measuring the electric-field gradient at the site of the radioactive probe atom 111 In by the perturbed γγ angular correlation technique. It is shown that implantation of In into CdS with subsequent annealing drives 100% of the In atoms to Cd lattice sites. Diffusion of In into CdS under S overpressure results in the formation of In Cd -V Cd pairs which seem to be responsible for the self-compensation of In donors in CdS.

Photoluminescence analysis of semiconductors using radioactive isotopes

The combination of photoluminescence spectroscopy with the radioactive isotopes 7Be, 71As, 111Ag, 111In, 191Pt, 193Au and 197Hg is shown to provide definitive proof of the chemical identity of impurities producing photoluminescence spectra in all classes of semiconductors. The isotope 71As is used to show that radioactive isotopes can provide a powerful means of producing and studying a fundamental crystal defect such as an anti-site. Factors governing the luminescence intensities which can lead to apparently anomalous results are also discussed.

Hydrogen passivation of cd acceptors in III–V semiconductors studied by PAC spectroscopy

Abstract Formation, structure, and stability of hydrogen correlated complexes, created at Cd acceptors in GaP, InP, and InAs have been studied after plasma charging as well as after H+ and/or He+ implantation at different energies. The different complexes were monitored by the perturbed angular correlation technique (PAC). In InP and Gap, the stability of Cd-H pairs is very similar for comparable Cd concentrations (ED = 1.4(2) eV and ED = 1.5(1) eV). In InAs, two different hydrogen correlated configurations are observed, one could be identified as Cd-H pair, oriented in 〈111〉 lattice direction (νQ = 427 MHz, η = 0). The second complex involves at least one H atom and radiation defects or, favoured by a defect induced, secondary mechanism several hydrogen atoms.

Characterization of Cd implanted and annealed GaAs and InP by perturbed angular correlation (PAC) spectroscopy

Abstract Investigations of 111m Cd implanted GaAs and InP crystals using the microscopically sensitive perturbed angular correlation technique show that the implanted Cd is incorporated on unperturbed substitutional lattice sites during rapid thermal annealing at significant lower temperatures than for electrical activation is required. In GaAs the higher implantation temperature at 473 K did not show any influence on this annealing stage, whereas as higher implantation dose hinders the annealing. We conclude that not only the local environment of the implant but also the long-range lattice perfection has to be restored for the electrical activation of implants in III-V compound semiconductors.

Hydrogen passivation of acceptors in silicon: a combined PAC and resistivity study

Abstract PAC measurements at 111 In, yielding information on the amount of formed In-H pairs, and four point resistivity measurements were combined to study the correlation between pair formation and electrical deactivation of acceptors in p-Si samples during passivation with H and thermal reactivation. Passivation was performed by means of low energy (200 eV) H + implantation which proved to be quite efficient at 400 K. A complete passivation of the In profile with a peak concentration of 10 18 cm −3 could be achieved. The results show, that the deactivation and reactivation of the In acceptors quantitatively coincide with the formation and dissociation of In-H pairs.

Microscopic Study Of The Hydrogen Diffusion In III-V Semiconductors

The authors report on experiments which observe on a microscopic scale the migration of isolated hydrogen in InP, GaAs, and InAs. Using the radioactive acceptor {sup 117}Cd, Cd-H pairs have been formed in these III-V semiconductors. After the decay of {sup 117}Cd to {sup 117}In, H is no longer bound to an acceptor and can diffuse freely. This diffusion has been observed by perturbed {gamma}{gamma} angular correlation (PAC) spectroscopy. At 10 K, the occupation of two different lattice sites by hydrogen has been observed. First results on the diffusion of hydrogen will be discussed.