O. Procházková

Hydrogen sensors based on electrophoretically deposited Pd nanoparticles onto InP

Electrophoretic deposition of palladium nanoparticles prepared by the reverse micelle technique onto InP substrates is addressed. We demonstrate that the substrate pre-deposition treatment and the deposition conditions can extensively influence the morphology of the deposited palladium nanoparticle films. Schottky diodes based on these films show notably high values of the barrier height and of the rectification ratio giving evidence of a small degree of the Fermi level pinning. Moreover, electrical characteristics of these diodes are exceptionally sensitive to the exposure to gas mixtures with small hydrogen content.

Role of f-Elements in the Growth of InP Layers for Radiation Detectors

We report the effect of f-element addition (Er, Ho, Nd, Pr, Tb and Yb) during the liquid phase epitaxy (LPE) on the growth process and structural, electrical and optical properties of thick InP epitaxial layers for applications in ionizing radiation detector structures. The layers were grown by LPE from the melt containing, besides essential components, also rare-earth (RE) elements admixture. The grown layers were examined by low-temperature photoluminescence spectroscopy and temperature-dependent Hall effect. We have demonstrated that the concentration of shallow donors was reduced effectively by up to three orders of magnitude. Room temperature Hall effect measurements revealed p-type conductivity of the layers prepared from the melt containing Tb, Pr or Yb admixture exceeding certain limiting concentration. From among the studied RE elements Pr and Tb appear as the most promising candidates for the preparation of pure and thick (d ≥ 10 μm) InP layers with p-type conductivity. These layers could readily be used for the preparation of α-particles detectors, where detection will be mediated via the depletion layer of high quality Schottky contact.

Electrical resistivity and photoluminescence of lead iodide crystals

Direct synthesis of lead iodide, a promising material for X-ray and γ detectors operating at room temperature, was developed and optimized. The influence of admixture of rare earth elements Ce, Ho, Gd, Yb, Er, and Tb in concentrations 0.05–0.5 at. % on the quality of prepared PbI2 was investigated. Zone melting was employed in order to increase the lead iodide purity. Electrical and optical properties of PbI2 samples were assessed on the basis of the measurement of electrical resistivity and low-temperature photoluminescence. The electrical resistivity of synthesized samples varied from 109 Ω cm to 1011 Ω cm and occasionally it was increased up to 1013 Ω cm.

Effect of rare earth addition on liquid phase epitaxial InP-based semiconductor layers

Abstract The influence of rare earth (RE) element (Ho, Er or Nd) addition during liquid phase epitaxial growth (LPE) on the electro-optical properties of InP and GaInAsP semiconductor layers has been studied. The effect of Nd admixture is reported for the first time. Series of InP-based layer samples were prepared by LPE from the melt containing 0–0.35 wt.% of RE admixture. Temperature-dependent Hall effect and capacitance–voltage curves show a quite dramatic impact of Er or Nd on donor and free-carrier concentrations: they were decreased by as much as three orders of magnitude in some cases. Low-temperature photoluminescence (PL) spectra have been measured for various levels of excitation power. The major manifestation of the RE admixture was the pronounced narrowing of PL curves and the corresponding appearance of the fine features in the excitonic band, characteristic of pure material, low in defects. The effects are attributed to RE atoms acting as very efficient gettering agents.

Preparation of Lead Iodide as Input Material for X-Ray Detectors

The aim of this work is to study the new method of direct synthesis of lead and iodine as the input material of PbI2. This method has not been studied for this material till now, and seems to be one of the new methods for preparation of the input material. The photoluminescence measurement and measurement of resistivity has been done and compared with the measurements done by precipitation and zone purification.

P-type InP grown by liquid phase epitaxy with rare earths: not intentional Ge acceptor doping

Abstract InP single crystal layers were grown by liquid phase epitaxy (LPE) on semi-insulating InP:Fe substrates with praseodymium added to the melt. Room temperature Hall effect measurements revealed p-type conductivity of the layers with the hole concentration 6×10 14 cm −3 and mobility 150 cm 2 V −1 s −1 . By measuring temperature dependence of the hole concentration the binding energy of the dominant acceptor was determined as 223 meV. A photoluminescence line was found at 1.195 eV, close to the previously estimated no-phonon line of Ge acceptor transitions in Ge doped n-type InP. It was concluded that Ge acceptors cause the p-type conductivity of the grown layers.

Characterisation of InP and GaInAsP layers prepared by liquid-phase epitaxy using holmium doping and gettering

A series of InP and GaInAsP (λg = 1.3 μm) layer samples were prepared by liquid-phase epitaxy from melts containing 0–0.5 wt.% of the rare-earth element holmium. The growth process was carried out in a horizontal multiple-bin graphite boat in a high-purity H2 atmosphere. The layers were grown on (100)-oriented InP substrates at 630 °C. The samples were examined by various physical diagnostic techniques; among them, photoluminescence spectroscopy was the most important. There are no indications of the holmium ions being incorporated into the host lattice sites to form optically active centres. The impact of a Ho admixture is nonetheless quite dramatic, especially on the carrier density, which is decreased by two-and-a-half orders of magnitude, and on the photoluminescence spectra which become markedly narrowed and their fine features are resolved. These effects are attributed to holmium acting as a very efficient gettering agent with regard to shallow donors. AIIIBV semiconductor layers with low background carrier concentrations are of interest for high quality detectors and devices destined for very high frequency operation.

Role of Rare-Earth Elements in the Technology of III-V Semiconductors Prepared by Liquid Phase Epitaxy

First applications of rare-earth (RE) elements in semiconductor technology are rooted in radiation tolerance improvements of silicon solar cells and purification of GaP crystals. The idea was later adopted in the technology of germanium and compound semiconductors. Since the 1980’s, considerable attention has been directed towards REs applications in III-V compounds both for epitaxial films and bulk crystals (Zakharenkov et al., 1997). The uniqueness of REs arises from the fact that the lowest-energy electrons are not spatially the outermost electrons of the ion, and thus have a limited direct interaction with the ion’s environment. The shielding of the 4f electrons by the outer filled shells of 5p and 5s electrons prevents the 4f electrons from directly participating in bonding (Thiel et al., 2002). The RE ions maintain much of the character exhibited by a free ion. This non-bonding property of the 4f electrons is responsible for the well-known chemical similarity of different REs. Since transitions between the electronic states of the shielded 4f electrons give rise to spectrally narrow electronic transitions, materials containing REs exhibit unique optical properties. By careful selection of the appropriate ion, intense, narrow-band emission can be gained across much of the visible region and into the near-infrared (Kenyon, 2002). Inspired by the striking results accomplished in the field of optical amplifiers and lasers based on REdoped fibres (Simpson, 2001), substantial research activity has been recently carried out on RE-doped semiconductor materials for optoelectronics (Klik et al., 2001). In most cases, however, achieving effective doping of III-V compounds by REs during growth from the liquid phase has proven difficult; the high chemical reactivity and the low solid solubility are the main restrictions on introducing RE atoms into the crystal lattices (Kozanecki & Groetzschel, 1990). On the other hand, the enhanced chemical affinity of REs towards most species of the shallow impurities leads to the formation of insoluble aggregates in the melt. Under suitable growth conditions, these aggregates are rejected by the growth front and are not incorporated into the grown layer: gettering of impurities takes place. Especially Si and main group-six elements acting as shallow donors in III-V semiconductors are effectively gettered due to REs high affinity towards them (Wu et al., 1992). Removal of detrimental impurities is of vital importance in applications such as PIN 13

Preparation and Characterization of TeO2 Based Glasses

Binary and ternary TeO2 based oxy-chloride glass systems have been prepared and characterised by absorption and low-temperature photoluminescence spectroscopy, and by the measurements of dc electrical conductivity. Prepared glasses exhibit transmittance 75-80% in a broad transmission range 0.3 – 6.5µm with modest shift of upper absorption edge to longer wavelength as heavier ions are introduced into the system. Electronic transitions between 4f-4f inner shells of Pr3+ ions embedded into the host glass have been investigated in a wide temperature range as a function of used precursors used for doping. The temperature dependence of dc electrical conductivity exhibits Arrhenius plots with the single activation energy. PACS codes 81.05.Kf, 78.20.Ci, 78.55.Hx

P-type InP grown by liquid phase epitaxy from melts with rare earth admixtures

InP single crystal layers were grown by liquid phase epitaxy (LPE) on semi-insulating InP with various rare earth elements added to the melt. The layers were characterized by temperature dependent Hall measurements and low temperature photo-luminescence spectroscopy. The work is focused on studying p-type InP grown with Tb and Yb admixtures. The dominant acceptor in the case of Tb was identified as Mn on the In site. In the case of Yb the dominant acceptor was identified as isoelectronic Yb on the In site subjected to a strong electron-lattice interaction.