Hydrogen-related Shallow Donors Research Articles

High-throughput and cost-effective method for production of high-quality semi-insulating InP substrates

A novel technique for preparation of high-resistivity indium phosphide (InP) via post-growth treatment of undoped n-type wafers is presented. The method includes the deposition of a controlled quantity of iron on both faces of as-cut wafers by a simple chemical bath, and the subsequent Fe diffusion by thermal annealing. The reproducible low - to – high resistivity conversion is explained considering two simultaneous phenomena: the annealing-controlled in-diffusion of Fe deep acceptors and the out-diffusion of hydrogen-related shallow donors. Differently from standard Fe-doped melt-grown InP single crystals, this process does not suffer from segregation, thus the Fe-concentration is constant from wafer to wafer, with no striations and radial gradients deriving from the convex solid–liquid interface during growth. Main advantages of the developed process are: i) an entire undoped InP boule may be sliced and converted to semi-insulating, which makes the process cost-effective; ii) reproducible and uniform semi-insulating properties from batch to batch of wafers; iii) the Fe incorporation is precisely controlled, and minimized, so that electrical characteristics of Fe-diffused wafers are superior to those of traditional semi-insulating melt-grown InP crystals doped via addition of elemental Fe to the melt.

Influence of oxygen on trap-limited diffusion of hydrogen in proton-irradiated n-type silicon for power devices

The growing demand for power devices has led to the use of magnetic field-applied Czochralski (m:Cz) wafers owing to the limited production capacity and available diameters of the traditionally used floating zone (FZ) wafers. Consequently, the influence of oxygen impurities in the wafers on the electrical properties of devices, regardless of the growth method, needs to be investigated to achieve a stable fabrication process for power devices. Using the proton irradiation doping process and spreading resistance profiling technique, we evaluated the effective diffusion coefficient (Deff) related to trap-limited diffusion of hydrogen and the effects of impurities on diffusivity. We irradiated n-type silicon wafers, which have different carbon, oxygen, and phosphorus concentrations, with 2 MeV protons and annealed them at 300–400 °C. By analyzing the width of the n-type region, where hydrogen-related shallow donors (HDs) are induced, we estimated Deff to be five to six orders of magnitude lower than the intrinsic diffusion coefficient, indicating that hydrogen motion is highly trap-limited. Deff was significantly dependent on the oxygen concentration, and the activation energy of hydrogen diffusion varied from 0.57 ± 0.15 eV (pure epitaxial wafer) to 2.19 ± 0.15 eV (m:Cz wafer). This trend suggests that oxygen-related defects preferentially trap the mobile hydrogen released from thermally dissociated HDs. This study also reveals that the diffusion coefficients of different materials when annealed at 400 °C are comparable. This information is essential to realize the cost-effective production of power devices because we can treat m:Cz and FZ wafers equivalently during the doping process.

Photoluminescence studies on structural defects and room temperature ferromagnetism in Ni and Ni–H doped ZnO nanoparticles

We explore the effects of hydrogenated annealing on the crystal structure, room temperature ferromagnetism (RT-FM) and photoluminescence (PL) properties of Ni-doped ZnO (Zn1−xNixO, x=0.0 to 0.2) nanoparticles prepared by a sol-gel method. The x-ray photoelectron spectra and x-ray diffraction data provide evidence that Ni has been incorporated into the wurtzite ZnO lattice as Ni2+ ions substituting for Zn2+ ions at x≤0.05. A secondary phase of NiO type begins to form inside ZnO when x>0.05 and segregates from ZnO host lattice at x=0.2, leading to a large variation in the lattice constants of ZnO. The magnetization measurements show that the saturation magnetization (Ms) increases with increasing Ni concentration in the single-phase Zn1−xNixO (x≤0.05) nanoparticles. The secondary phase formation reduces the magnetization of Zn1−xNixO (x=0.1 and 0.15), while the segregation of NiO from the ZnO lattice at x=0.2 is accompanied by a large increase in Ms again. The PL measurements show that the UV emission intensity of single-phase Zn1−xNixO (x≤0.05) nanoparticles increases with a blueshift in the UV emission line when the Ni concentration increases, while the dominant green emission intensity decreases with increasing Ni dopant. The PL data strongly suggest that the FM in single-phase Zn1−xNixO (x≤0.05) nanoparticles is intrinsically correlated with a doping induced increase in the electron concentration in the conduction band of Ni-doped ZnO. After H2-annealing, the single-phase Zn1−xNixO:H (x≤0.05) nanoparticles show increases in both coercivity and saturation magnetization. The PL and diffuse reflectance spectra suggest that hydrogen-related shallow donors and an improved sample quality may be responsible for the H2-annealing induced enhancement of the RT-FM. The obvious correlation between FM and carrier concentration in Ni and Ni–H doped ZnO points towards a mechanism of carrier-mediated FM for Ni-doped ZnO diluted magnetic semiconductors.

Improved electrical stability and UV emission of zinc oxide thin films prepared by combination of metalorganic chemical vapor deposition technique and post-deposition hydrogen doping

Fourier transform infrared and photoluminescence spectroscopy provide strong evidence that post-deposition hydrogen doping of polycrystalline zinc oxide (ZnO) thin films improves the resistivity by increasing hydrogen-related shallow donors and hydrogen passivation of native defects. Improvement of the electrical stability and UV emission confirm that post-deposition hydrogen doping is a promising method to achieve high quality ZnO thin films for the use as transparent electrodes and/or UV light emitters in thin-film-based optoelectronic devices.

Hydrogen-related shallow donors in Ge crystals implanted with protons

Electrical properties of germanium crystals, which were subjected to implantation with 300 keV protons (H +) and subsequent anneals, have been studied by means of capacitance–voltage and spreading resistance probe techniques and deep level transient spectroscopy. It was found that heat-treatments of the proton-implanted samples in the temperature range 200–300 °C resulted in the formation of shallow hydrogen-related donors. The maximum concentration of the donors was about 2×10 16 cm −3 for a H + fluence of 1×10 15 cm −2. An analysis of changes in the spatial distribution of the H +-related donors upon isothermal and isochronal anneals showed that the donors appeared in the region which is close to the projected depth of implanted protons at the initial stages of heat-treatments in the temperature range of 200–300 °C and spread out of this region upon an increase in annealing time or annealing temperature. The depth of the layer where the donors were formed after a heat-treatment at 250 °C for 9.5 h exceeded the projected length protons by more than one order. Diffusion coefficients of mobile species responsible for the formation of the donors were determined. An analysis of the diffusion coefficients, which were obtained, allowed us to suggest that the H-related donors could be complexes of hydrogen atoms with intrinsic point defects. These complexes were formed in the implantation damage area and diffused as whole units upon annealing. Some indications of the shallow-deep bistability of the donors were found.

Hydrogen-plasma-induced thermal donors in high resistivity n-type magnetic Czochralski-grown silicon

In this work, the formation of donors in n-type high resistivity magnetic Czochralski-grown silicon wafers, directly exposed to a hydrogen plasma, is investigated by a combination of capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements. C-V analysis demonstrates diffusionlike concentration profiles close to the surface, pointing to the formation of hydrogen-related shallow donors in silicon during the hydrogenation. In addition, oxygen thermal donors are created during a subsequent annealing (20min) performed at 350–450°C, as demonstrated by DLTS. It is shown that the hydrogen-related shallow donors are the dominant donors in as-hydrogenated samples, while hydrogen acts as a catalyst during the formation of oxygen thermal donors in the temperature range of 350–450°C. It is finally shown that the formation of both kinds of donors is Fermi-level dependent.

On the nature of hydrogen-related shallow donors in ZnO

Vapor-phase grown ZnO samples treated with hydrogen plasma were studied by means of photoconductivity and IR absorption spectroscopy. Three bands at 180 , 240 , and 310 cm - 1 were observed in the photoconductivity spectra of hydrogenated ZnO. These are identified as electronic transitions of three independent hydrogen-related shallow donors. Two electronic transitions from the H–I defect previously associated with the bond-centered hydrogen were found in IR absorption spectra at 1430 and 1480 cm - 1 . Based on the energies of these transitions H–I was ruled out as a candidate for the hydrogen-related shallow donor in ZnO.

DLTS Study on Deep Levels Formed in Plasma Hydrogenated and Subsequently Annealed Silicon

P-n junctions are created in p-type Czochralski silicon after a low temperature (270°C) hydrogen plasma exposure. This is attributed to the formation of hydrogen-related shallow donors. A deep level (E1) with an activation energy of about EC-0.12 eV is observed by DLTS measurement and assigned to a metastable state of the hydrogen-related shallow donors. At an annealing temperature of 340°C, the E1 centres disappear and oxygen thermal donors appear. The concentrations of the oxygen thermal donors are found typically to be 2-3 decades lower than that required for over-compensating the initial p-type doping and for contributing the excess free carriers.

Photoconductivity and infrared absorption study of hydrogen-related shallow donors in ZnO

Vapor phase grown ZnO samples treated with hydrogen and∕or deuterium plasma were studied by means of photoconductivity and infrared (IR) absorption spectroscopy. Three bands at 180, 240, and $310\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ were observed in the photoconductivity spectra of hydrogenated ZnO. These are identified as electronic transitions of three independent hydrogen-related shallow donors. Two electronic transitions from the $\mathrm{H}\text{\penalty1000-\hskip0pt}\mathrm{I}$ defect previously associated with the bond-centered hydrogen [E. V. Lavrov et al., Phys. Rev. B 66, 165205 (2002)] were found in IR absorption spectra at 1430 and $1480\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. Based on the energies of these transitions $\mathrm{H}\text{\penalty1000-\hskip0pt}\mathrm{I}$ was ruled out as a candidate for the hydrogen-related shallow donor in ZnO.

Doping of Oxidized Float Zone Silicon by Thermal Donors - a Low Thermal Budget Doping Method for Device Applications?

AbstractThermal donor formation was studied in oxygen enriched high resistive float zone silicon (FZ Si:Oi). Such substrates are used e.g. for radiation hard detectors or high voltage devices. RF Plasma hydrogenation (110 MHz, 50 W) was carried out at 250°C for 1 hour. Subsequent annealing was done at 450°C/air for up to 50 h. The plasma treated and annealed FZ Si:Oi samples were analyzed by spreading resistance probe, capacitance-voltage and DLTS measurements. It is shown that a rapid formation of donors can be observed in oxidized FZ Si:Oi, but in a somewhat different way than in Czochralski (Cz) Si. While in Cz Si the hydrogen enhanced formation of ‘old’ thermal double donors occurs under the applied processes, in FZ Si:Oi most probably the formation of new hydrogen related shallow donors can be assumed.

Hydrogen-related shallow donors in irradiated and heat-treated CzSi crystals

The displacement of germanium (Ge) atoms induced by arsenic (As) ion implantation at room temperature was investigated using Ge isotope superlattices grown by molecular beam epitaxy. The depth profiles of 74Ge isotopes in the 70Ge/natGe isotope superlattices before and after ion implantation were obtained by secondary ion mass spectrometry. By representing the experimental data using a conventional integral model, Ge atomic displacement as a function of depth was obtained, from which we determined that 0.75 nm is the critical displacement necessary to make the structure appear amorphous under examination by cross-sectional transmission electron microscopy. However, we found that the amorphous Ge layers were recrystallized due to a local elevation of temperature caused by the implantation, which indicates that the samples should be cooled down during implantation to avoid the regrowth of amorphous Ge layers for this analysis.