J. Zavadil

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.

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.

Preparation of InP-based semiconductor materials with low density of defects: effect of Nd, Ho and Tb addition

Abstract Specific features of some rare earth elements (REE=Nd, Ho or Tb) are exploited to improve structural, optical and electrical properties of InP-based layer compounds for applications in ionising radiation detector structures. InP layers were grown by liquid phase epitaxy on (100)-oriented single crystal InP substrates with individual REE addition to the melt. The dependence of the layer thickness, overall surface morphology and defect density on the growth conditions were monitored by employing optical and scanning electron microscopy. The evaluation of electrical properties was gained from C–V measurements performed with the mercury probe and from a free carrier concentration profile determined by the probe profiling method on bevelled samples. The low-temperature photoluminescence spectroscopy was used to study the changes in optical properties. Significant improvement of all the studied layer parameters with increasing amount of REE in the melt was observed up to certain critical value of REE concentration. The density of structural defects was reduced by more than a half order of magnitude, free carrier concentration was reduced effectively by up to four orders of magnitude, photoluminescence peaks were narrowed substantially and fine spectral features were resolved. The conductivity of layers prepared with Tb admixture changed from n to p type when Tb exceeded certain limit of concentration in the melt.

LPE InP layers grown in the presence of rare-earth elements

Abstract Preparation and characterisation of InP layers grown by Liquid Phase Epitaxy with the addition of several rare-earth (RE) elements into the growth melt is reported and the influence of Ho, Er, Nd Pr, and Yb is compared. Low-temperature photoluminescence (PL) spectra have been measured for various levels of excitation power and temperature. The major manifestation of the RE admixture is the pronounced narrowing of PL curves and the corresponding appearence of fine spectral features. Particularly in the case of Nd and Pr admixtures the acceptor related PL band exhibits a structure that permits an individual determination of acceptor and donor binding energies. Temperature dependent Hall effect and capacitance–voltage curves also show quite dramatic impact of Pr and Nd on shallow impurity and free-carrier concentrations: they were reduced by as much as three orders of magnitude.