P-type High Purity Research Articles

Modeling the charge collection efficiency in the Li-diffused inactive layer of P-type high purity germanium detector

A model of the Li-diffused inactive layer in P-type high purity germanium detectors is built to describe the transportation of charge carriers and calculate the charge collection efficiency therein. The model is applied to calculate charge collection efficiency of a P-type point-contact germanium detector used in rare event physics experiments and validated in another P-type semi-planar germanium detector. The calculated charge collection efficiency curves are well consistent with measurements for both detectors. Effects of the Li doping processes on the charge collection efficiency are discussed based on the model. This model can be easily extended to other P-type germanium detectors, for instance, the P-type broad-energy Ge detector, and the P-type inverted-coaxial point-contact detector.

Prototyping experience with Ge micro-strip sensors for EDXAS experiments

Energy dispersive X-ray spectrometers provide a method for the fast data acquisition of X-ray absorption spectra. The intensity of the spectral components of a polychromatic beam is detected simultaneously after being dispersed in space, and being transmitted by an experimental sample. The cryogenic detector system called XH deploys a germanium micro-strip sensor to perform such measurements. Here, the geometrical position of each strip is correlated to a specific spectral component of the dispersed beam.The prototyping experience reported in this work is related to the upgrade of the cryostat unit of the XH detector system. This upgrade was carried out in collaboration with beam-line ID24 at the European Synchrotron Radiation Facility (ESRF).Two 90 mm wafers of p-type high purity germanium were manufactured. Wafers contained test structures and micro-strip sensors made of 1024 strips with 50μm pitch. Electrical and in-beam tests were performed to verify the performance of this technology. The measurements included capacitance–voltage characteristics; stress-tests like temperature cycling testing and burn-in tests; leakage current as a function of sensor temperature; charge-collection as a function of time; a test-run of a pump and probe experiment.Results are reported below showing that this sensor technology survived the extensive thermal and electrical stress-tests, and that it was able to measure the physical variations created by a laser shock on a sample of Fe–10%wtNi.

Experimental Investigation on the Photopeak Efficiency of a Coaxial High Purity Germanium Detector for Different Geometries

Purpose: Gamma spectrometer systems are complex instruments, and the quality of the numerical results they provide strongly depends on their reliable calibration. In this study, it was aimed to determine the full-energy peak efficiencies of a 40% p-type High Purity Germanium HPGe detector for point source, Marinelli beaker, and cylindrical container geometries in the 200-1500 keV energy range. Methods: The efficiency calibration of the HPGe gamma spectrometry system was performed using certified calibration sources. Efficiency values were determined using the gamma ray spectrum acquired for every calibration source.Results: Two different efficiency curves, at the linear scale and logarithmic scale-fitting, experimental efficiencies were plotted. The functions and parameters that fitted the efficiency curves were obtained by a computer program.Conclusion: The photopeak efficiencies decrease as energy increases and the observed efficiency curves were closely with similar studies

The impact of neutral impurity concentration on charge drift mobility in p-type germanium

We reported a new result of the neutral impurity scattering of holes that has impact on the charge drift mobility in high purity p-type germanium crystals at 77 Kelvin. The charge carrier concentration, mobility and resistivity are measured by Hall Effect system at 77 Kelvin. We investigated the contribution to the total charge drift mobility from ionized impurity scattering, lattice scattering, and neutral impurity scattering with the best theoretical models and experimental data. Several samples with measured Hall mobility from the grown crystals are used for this investigation. With the measured Hall mobility and ionized impurity concentration as well as the theoretical models, we calculated the neutral impurity concentration by the Matthiessen's rule. As a result, the distributions of the neutral impurity concentrations with respect to the radius of the crystals are obtained. Consequently, we demonstrated that neutral impurity scattering is a significant contribution to the charge drift mobility, which has dependence on the concentration of neutral impurities in a given germanium crystal.

Effect of annealing on contact performance and electrical properties of p-type high purity germanium single crystal

Van de Pauw Hall measurement is an effective method to characterize the properties of semiconductors, such as bulk concentration, mobility, and resistivity, all of which are used to describe the purity level in the semiconductors. However, the performance of the ohmic contacts has a direct impact on the reliability and accuracy of the results obtained from the Van de Pauw Hall measurement. In the present work, the influences of different annealing techniques on the performance of the InSn ohmic contacts have been investigated using a High Purity Germanium (HPGe) crystal sample. The results show that the preferred annealing condition is at 400 °C for 1 hour, which has provided a significant improvement of the InSn contact quality and microscopic homogenization of the impurities in the HPGe crystal. The carrier concentration, charge mobility, and resistivity of the sample annealed at 400 °C for 1 hour are 5.772×1010/cm3, 1.883×104× cm2/Vs, and 5.795×103×Ω cm at 77 K, respectively.

Particle detectors based on InP Schottky diodes

A study of electrical properties and detection performance of Indium Phosphide detector structures with Schottky contacts prepared on high purity p-type InP was performed. Schottky barrier detectors were prepared by vacuum evaporation of Pd on p-type epitaxial layers grown on Zn-doped p-type substrates. The detection performance of the detectors was characterized by the measurement of pulse-height spectra with alpha particles emitted from 241Am source at room temperature. The influence of the quality of p-type epitaxial layers on the charge-collection efficiency and energy resolution in the full-width half-maximum is discussed.

Particle detectors based on semiconducting InP epitaxial layers

A study of electrical properties and detection performance of two types of Indium Phosphide detector structures was performed: (i) with p-n-junction and (ii) with Schottky contact prepared on high purity p-type InP. The p-n junction detectors were based on a high purity InP:Pr layers of both n- and p- type conductivity with carrier concentration on the order of 1014 cm−3 grown on Sn doped n-type substrate. Schottky barrier detectors were prepared by vacuum evaporation of Pd on high purity p-type epitaxial layer grown on Mn doped p-type substrate. The detection performance of particle detectors was measured by pulse-height spectra with alpha particles emitted from 241Am source at room temperature.

Photo-thermal ionization spectroscopy of shallow acceptors in high purity germanium

The results of high sensitivity photo-thermal ionization spectroscoic (PTIS) investigation of shallow acceptors in high purity p-type germanium sample with room temperature resistivity of about 50Ω·cm, at temperature above liquid helium by Fourier transform spectrometer and associated magneto-optical measurement systems, are reported. The optimum photo-thermal ionization temperature range for the shallow impurities in high purity germanium is determined experimentally. At temperatures within this range, the PTIS spectra of this sample were measured. Boron and aluminum are found to be the main shallow acceptors in the sample. The causes of line splits of spectra, rapid recombination of compensating impurity and random strain, are analyzed and discussed.

LArGe: Background suppression using liquid argon (LAr) scintillation for 0 νββ decay search with enriched germanium (Ge) detectors

Measurements with a bare p-type high purity germanium diode (HPGe) submerged in a 19 kg liquid argon (LAr) scintillation detector at MPIK-Heidelberg are reported. The liquid argon–germanium system (LArGe) is operated as a 4π anti-Compton spectrometer to suppress backgrounds in the HPGe. This R&D is carried out in the framework of the Gerda experiment which searches for 0νββ decays with HPGe detectors enriched in 76Ge. The goal of this work is to develop a novel method to discriminate backgrounds in 0νββ search which would ultimately allow to investigate the effective neutrino mass free of background events down to the inverse mass hierarchy scale. Other applications in low-background counting are expected.

An empirical function for the full energy peak efficiency for a P-type Co-axial high purity germanium detector

An empirical analytical function has been obtained for the full energy peak efficiency of a co-axial P-type High Purity Germanium Detector for gamma-ray energies in the range of 80 - 1333 keV and source-to-detector distance in the range of 1.0 - 4.0 cm. Comparison of the calculated efficiencies with the corresponding experimental value agrees very well within standard deviations of 1.8 - 3.7 %. JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 2 No. 1 (2000) pp. 64-70

Deep defects in n-type high-purity germanium: quantification of optical variants of deep level transient spectroscopy

The characterization of high-purity (HP) Ge for the fabrication of γ-ray detectors poses very specific demands due to the high degree of purity of the material (shallow concentration of the order 109–1010cm−3). Deep level transient spectroscopy (DLTS) may still be applied to this kind of material since the sensitivity is relative to the shallow doping concentration. In contrast with p-type HP Ge which was characterized extensively in the 1980s, very little is known about deep defects in n-type HP Ge. Two optical variants of DLTS have been applied to n-type HP Ge and quantified for the first time. Several deep minority carrier traps are detected and identified as mainly Cu-related traps with concentrations in the 106–108cm−3 range. These Cu-related traps, which are well known as the majority carrier traps appearing in typical p-type HP Ge, are thus present as minority carrier traps in typical n-type HP Ge. The conclusion that deep-level defects in n- and p-type HP Ge are very similar could be expected from the similarity in growing conditions for the two types of materials. In the first DLTS variant, known as optical DLTS or ODLTS the deep levels are filled by optical injection (with light of above bandgap energy) at the back ohmic contact of a reverse biased diode. The spectrum is generated by the capacitance transients following the optical excitation. In the second variant, known as photo induced (Current) transient spectroscopy or PI(C)TS the deep levels are also filled optically with intrinsic light, but here a neutral structure is used with two ohmic contacts in sandwich configuration. The spectrum is generated by current transients instead of capacitance transients. This method is especially suited for high-resistivity or semi-insulating materials which cannot be measured with capacitance-based DLTS. PICTS was applied to n-type Ge with a shallow concentration as low as 109cm−3.

The High Purity Germanium Detector Whole Body Monitor at PSI

For the in vivo monitoring of radiation workers a new measurement system has been installed at PSI, Switzerland. A single p-type high purity germanium detector of 102% relative efficiency is mounted in a shielded room located in a subterranean shelter. The room has internal dimensions of 270 cm × 190cm × 220 cm and is constructed of iron from old railway rails. The detector is mounted on a mechanical support fixed on the ceiling, which permits movements in three directions and two axes. Measurements of radionuclides in the body are performed in a sitting position. The system is used to detect the presence of radionuclides that emit photons with energies between 50 keV and 2 MeV. A description of the system is presented. The results of calibration of the detector for total-body activity measurements are discussed. The performances of the new system and the old Nal(TI) body monitor used at PSI are compared.

Optical deep level transient spectroscopy of minority carrier traps in n-type high-purity germanium

Deep levels in n-type high-purity (HP) detector grade germanium are studied using optical deep level transient spectroscopy (ODLTS). In this technique, optical injection (using light of above band gap energy) from the back ohmic contact together with a suitable sample configuration results in the detection of centers in the minority half of the band gap. Six deep minority carrier traps are detected in typical n-type HP germanium which turn out to be the same defects as found earlier in typical p-type HP germanium as majority carrier traps. These deep defects are mainly copper related. A formula is deduced to calculate concentrations from the ODLTS spectra. It is shown that in n- and p-type HP germanium not only the same defects are present but that their concentrations are also comparable.

Radiation damage in large-volume n- and p-type high-purity germanium detectors irradiated by 1.5 GeV protons

Excellent energy resolution makes germanium detectors prime candidates for gamma-ray spectroscopy in space missions. We present a study of several large-volume n-type and p-type high purity,germanium (HPGe) detectors that were damaged by 1.5 GeV protons and examine their performance as function of fluence, operating and anneal temperature, and time. n-type detectors exhibit essential advantages for space applications over p-type detectors. Annealing at about 110 K for both detector types was observed as well as resolution transients up to 134 K. We discuss the observed radiation effects with respect to existing models and show their limitations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Impurity Wave Function and Alloy Broadening of Impurity-Related Luminescence

By performing state-of-art ckputations of the acceptor wave func- tions in GaAs we show that the linewidth of the conduction band to ac- ceptor luminescence increases more than qu^adratically with the increase in the binding energy. This proves that study of the fluctuation broadening of the impurity-related emission in semiconductor alloys may provide a critical test for theories claiming realistic impurity wave function computation. The theoretical results are compared with the experimental data for high purity p-type AlGaAs alloys.

Minority Carrier Diffusion Lengths for High Purity Liquid Phase Epitaxial GaAs

Measurements of minority carrier diffusion lengths for p-type and n-type GaAs were carried out using an electron beam induced current (EBIC) technique. The GaAs material was grown by liquid phase epitaxy (LPE) at the Australian Nuclear Science and Technology Organisation. The diffusion lengths measured for high purity p-type and n-type LPE-GaAs samples were observed to be longer than any previously reported.

Hall effect analysis of high purity p-type GaAs grown by metalorganic chemical vapor deposition

Variable temperature Hall effect and low temperature photoluminescence measurements have been performed on high purityp- andn-type GaAs grown at atmospheric pressure by metalorganic chemical vapor deposition. These high purity epitaxial GaAs layers were grown as a function of the arsine (AsH3) to trimethylgallium (TMG) ratio (V/III ratio). The accurate quantitative assessment of the electronic properties of thep-type layers was emphasized. Analysis of the material focussed on the variation of the concentration of the shallow impurities for different V/III ratios. Surface and interface depletion effects are included to accurately estimate the concentration of impurities. The model of the merging of the excited states of the acceptor with the valence band is used to include the dependence the activation energy of the impurity on the acceptor concentration as well as on acceptor species identity. The characteristicp- ton-type conversion with increasing V/III ratio was observed in these samples and the reason for thep- ton-type conversion is that the background acceptor concentration of carbon decreases and the germanium donor concentration increases as the V/III ratio is increased.

Electronic Stimulation of Acceptor Reactivation IN p - Type Hydrogenated GaAs

ABSTRACTThe mechanism of light-induced reactivation (LIR) of shallow substitutional acceptors in high-purity p-type hydrogenated GaAs has been investigated. Photoluminescence was used to determine the dependence of the rate and extent of this effect on photon energy, illumination intensity, as well as on sample temperature and chemical composition. At a sample temperature of 1.7 K a sharp threshold in the photon energy, Et, has been observed at about 7.5 meV below the bandgap energy of GaAs. This energy corresponds approximately to the onset of acceptorbound exciton absorption in the material. For photon energy E &lt; Et, only a weak reactivation effect is observed. The efficiency of reactivation increases dramatically for E &gt; Et, and for sufficiently large values of (light intensity).(illumination time) product the LIR process saturates. Both the extent of the subthreshold effect and the saturation level that is attainable with E &gt; Et are independent of the photon energy, excitation power and exposure time in the investigated range of these quantities. For E &gt; Et the initial LIR rate depends on the square of the light intensity, indicating a bimolecular reaction in terms of the photo-generated carrier densities. The observed strong dependence of the saturation level on the sample temperature during LIR is found to be consistent with the relative binding energies of different acceptor-hydrogen passivating complexes in GaAs. Based on these results, it is proposed that LIR of acceptors is electronically stimulated via recombination-enhanced vibrational excitation of acceptor-hydrogen complexes.

Correlation between deep-level parameters and energy resolution of p-type high purity Ge γ-detectors

A physical basis is presented for the previously reported correlation between deep levels in p-type high purity germanium and the energy resolution of corresponding γ-detectors. Taking account of re-emission of trapped holes at 77 K it is shown that effective hole traps are deeper than about E v + 0.07 eV. Slowly re-emitting traps may become saturated during detector operation. The detector resolution criterion L ≤ 2 keV is found to correspond with an upper limit of 4.5 × 10 9 cm −3 for the total active copper density. This density criterion is shown to be a reliable basis for the routine DLTS characterisation of high purity germanium production.

A large area solid state detector made of ultra high purity p-type Si

A Surface Barrier Detector for environmental monitoring was fabricated with an ultrahigh purity p-type Si crystal. The crystal had a nominal resistivity of 50 kΩ cm, and Al was evaporated on the outer surface to form a positive electrode of 50 mm ø. The excellent light-tightness and adhesivity of the Al layer enables direct mounting of samples on the detector and decontamination of the surface with wetted soft tissues. The energy resolution for α and β particles is 36 and 33 keV fwhm respectively and simultaneous measurement of both α and β particles can be carried out. The detector fabrication procedure, its characteristics and application are reported in this paper.