Characterization methods for silicon photodiode and silicon sub-surface properties

This thesis considers the characterization of silicon photodiode and the applications of silicon photodiodes in precision metrology, and some aspects of the silicon material characterizations. Such material characterizations are required in the process of semiconductor device manufacturing, one example of which is the silicon photodiode manufacturing. The motivation for the research on radiometry reported in this thesis has been the development of optical metrology at the Helsinki University of Technology (HUT). Most of the applications for this research are found in the UV-metrology. Importance of the UV-metrology arises from the environmental importance of accurate gauging of optical power at these wavelengths. This thesis describes the derivation and experimental verification of simple mathematical models, based on Fresnel equations. These models have allowed significant reductions in the uncertainties of spectrophotometric and radiometric measurements, especially in the UV wavelengths. These measurements are carried out using silicon photodiode-based detection systems. The reductions achieved in the measurement uncertainties have been utilized in the detector-based realizations of optical quantities maintained as national standards at HUT. The structure and operating principle of silicon photodiodes brings up the process of manufacturing of these devices, and the material characterizations required during this process. Novel methods in machining of silicon wafers for semiconductor industry pose new challenges for these characterizations. One such challenge is the need to characterize sub-surface damage in silicon wafers, induced by abrasive machining. The measurement of the sub-surface damage in silicon was the goal set for the work on materials characterization reported here. Various potential solutions to this requirement have been studied in this thesis, some of which are based on the spectrophotometric research carried out at HUT. Complete solution to this requirement has not been found. This thesis compares a number of promising methods and combines their respective advantages in order to create a more comprehensive understanding on the subject under study.reviewe

Mise en pratique for the definition of the candela and associated derived units for photometric and radiometric quantities in the International System of Units (SI)

open8The purpose of this mise en pratique, prepared by the Consultative Committee for Photometry and Radiometry (CCPR) of the International Committee for Weights and Measures (CIPM) and formally adopted by the CIPM, is to provide guidance on how the candela and related units used in photometry and radiometry can be realized in practice. The scope of the mise en pratique recognizes the fact that the two fields of photometry and radiometry and their units are closely related through the current definition of the SI base unit for the photometric quantity, luminous intensity: the candela. The previous version of the mise en pratique was applied only to the candela whereas this updated version covers the realization of the candela and other related units used for photometric and radiometric quantities. Recent advances in the generation and manipulation of individual photons show great promise of producing radiant fluxes with a well-established number of photons. Thus, this mise en pratique also includes information on the practical realization of units for photometric and radiometric quantities using photon-number-based techniques. In the following, for units used for photometric and radiometric quantities, the shorter term, photometric and radiometric units, is generally used. Section 1 describes the definition of the candela which introduces a close relationship between photometric and radiometric units. Sections 2 and 3 describe the practical realization of radiometric and photon-number-based units, respectively. Section 4.1 explains how, in general, photometric units are derived from radiometric units. Sections 4.2–4.5 deal with the particular geometric conditions for the specific photometric units. Section 5 deals very briefly with the topic of determination of measurement uncertainties in photometry.openZwinkels, Joanne; Sperling, Armin; Goodman, Teresa; Acosta, Joaquin Campos; Ohno, Yoshi; Rastello, Maria Luisa; Stock, Michael; Woolliams, EmmaZwinkels, Joanne; Sperling, Armin; Goodman, Teresa; Acosta, Joaquin Campos; Ohno, Yoshi; Rastello, Maria Luisa; Stock, Michael; Woolliams, Emm

Mise en pratique for the definition of the candela and associated derived units for photometric and radiometric quantities in the International System of Units (SI)

The purpose of this mise en pratique, prepared by the Consultative Committee for Photometry and Radiometry (CCPR) of the International Committee for Weights and Measures (CIPM) and formally adopted by the CIPM, is to provide guidance on how the candela and related units used in photometry and radiometry can be realized in practice. The scope of the mise en pratique recognizes the fact that the two fields of photometry and radiometry and their units are closely related through the current definition of the SI base unit for the photometric quantity, luminous intensity: the candela. The previous version of the mise en pratique was applied only to the candela whereas this updated version covers the realization of the candela and other related units used for photometric and radiometric quantities. Recent advances in the generation and manipulation of individual photons show great promise of producing radiant fluxes with a well-established number of photons. Thus, this mise en pratique also includes information on the practical realization of units for photometric and radiometric quantities using photon-number-based techniques. In the following, for units used for photometric and radiometric quantities, the shorter term, photometric and radiometric units, is generally used. Section 1 describes the definition of the candela which introduces a close relationship between photometric and radiometric units. Sections 2 and 3 describe the practical realization of radiometric and photon-number-based units, respectively. Section 4.1 explains how, in general, photometric units are derived from radiometric units. Sections 4.2\u20134.5 deal with the particular geometric conditions for the specific photometric units. Section 5 deals very briefly with the topic of determination of measurement uncertainties in photometry.Peer reviewed: YesNRC publication: Ye

Extending the Lifetime of Optically Stimulated Dosimeters for Use in Output Checks at IROC- Houston

Purpose: Optically Stimulated Luminescent Dosimeters (OSLDs) are a prominent form of in-vivo dosimeter used both in clinics as well as for the audits of radiologicalequipment at the Imaging and Radiation Oncology Core (IROC)-Houston. Thesedosimeters have a recommended dose limit of 10 Gy due to a change in signal response with dose. To assist with the OSLD operation at IROC-Houston, evaluating the signal response of these dosimeters with IROC’s methodologies offers the potential to extend the dose limit past 10 Gy, improve the efficiency of handling OSLDs, and reduce the cost and time spent on commissioning OSLDs.Methods: The signal response of OSLDs were evaluated using the American Association of Physicists in Medicine (AAPM) Task Group (TG)- 191 recommendations. Evaluations of sensitivity and linearity characteristics were performed as accumulated dose increased. To re-use the OSLDs, the dosimeters were bleached. Four different monochromatic and one polychromatic light source was compared to the IROC light source to determine the impact that bleaching wavelength had on signal response. In addition, the OSLDs were evaluated for how the choice of bleaching light and accumulated dose affected signal regeneration. Finally, the response of OSLDs as a function of accumulated dose were evaluated as a function of different fractions of dose. Every irradiation was performed ona Co-60 beam at the same SSD of 80cm and field size of 24.5 x 24.5Results: For the IROC system, we found that the signal response of OSLDs are stable within 1% up to 23 Gy. After this point, the sensitivity beings to decrease. The sensitivity of each OSLD relative to each other, ks,i did not change up to 50 Gy showing that the sensitivity change amongst all the OSLDs was applied universally amongst the group. There is a well characterized change in the slope of the linearity correction factor as accumulated history increases. For chromatic effects, we find that lower wavelengths remove signal the fastest, but polychromatic sources preserve the signal response to a greater accumulated dose history. For charge repopulation, we find that the degree of charge repopulation is related to dose, time, and bleaching light though this effect is nonsignificant with the IROC the newly analyzed dose limit of ~15-20 Gy. We find that fractionations at 5 Gy and higher yield a greater signal response compared to reference dosimeters, with larger fractions leading to a greater signal response. The greatest effect measured was with 30 Gy fractions at a value of 6.4% greater signal compared to reference. The greater fractions also exhibited a steeper increase in slope of the linearity correction factor.Conclusion: IROC can extend the dose limit of 15-20 Gy of accumulated dose. Theamount of charge repopulation at this dose level is insignificant, so the OSLDs in storage do not need to be rebleached prior to reintroducing them back into operation. For the application of correction factors, , can re-use it’s commissioned value whereas a value of needs to be evaluated based on the dose history and fractions used

Positronannihilation i ultralåga temperaturer

Positron Annihilation Spectroscopy is a powerful tool for defect characterisation, especially vacancies. Various defect properties can be studied, including defect behaviour at low and high temperatures. Despite the technique having its roots in the mid-20th century, there is little research on fundamental positron behaviour at ultralow temperatures. In this thesis, Positron Annihilation Lifetime Spectroscopy and Doppler Broadening Spectroscopy, two sub-methods of the spectroscopy technique, were used to measure positron trap-free Ge in the temperature range of 14 mK-300 K. Since a positron trap-free sample was used, the purpose was not to study defect processes. Instead, the aim of the thesis was to investigate whether any interesting positron processes could be seen at ultralow temperatures in the annihilation data. Previous research in Al has shown no change in either lifetime or Doppler broadening below 77 K. Measuring the positron lifetime in the sample located in a cryostat required designing a special detector setup, as the count rate was greatly reduced due to geometry. To tackle this, lifetime detectors consisting of BaF2 scintillators and quartz-windowed photomultiplier tubes were used. In addition, both analogue and digital signal processing techniques were tested for the lifetime setup, with the digital method proving to be preferable. Doppler Broadening was measured with a high-purity germanium detector connected to a digital gamma spectrometer. The results show a decrease in S-parameter and an increase in W-parameter with decresing temprature, with the rate of change being greatest at ultralow temperatures. This behaviour is concluded to be due to incomplete positron thermalization. The positron lifetime results are more difficult to interpret, as setup challenges resulted in results of questionable accuracy. Still, the trend suggests no change in lifetime over the whole temperature interval, which is in accordance with previous research.Positronannihilationsspektroskopi är ett effektivt verktyg inom defektkarakteriseringsstudier, speciellt för att mäta vakanser. Olika defektegenskaper kan studeras med denna metod, såsom hur defekter beter sig i låga och i höga temperaturer. Trots att denna spektroskopiteknik har sina rötter i mitten av 1900-talet finns det begränsat med forskning i positroners beteende i ultralåga temperaturer. I denna avhandling användes Positronannihilationlivstidsspektroskopi samt Dopplerbreddningspektroskopi, två subspektroskopitekniker, för att mäta Ge som inte innehöll positronfällor i temperaturintervallet 14 mK-300 K. Eftersom provet inte innehöll positronfällor var avsikten ej att studera defektprocesser, utan att studera ifall några intressanta positronprocesser i ultralåga temperaturer kan observeras i annihilationsdatan. I tidigare forskning gällande Al har inga förändringar i varken positronlivstid eller dopplerbreddning observerats under 77 K. Att mäta positronlivstiden i provet inne i ett kryostat krävde en speciell detektoranordning, eftersom kryostatgeometrin resulterade i en mycket lägre pulsfrekvens än vanligt. Som åtgärd byggdes detektorer med BaF2-scintillatorer och fotomultiplikatorrör med kvartsfönster. Dessutom testades både analog och digital signalbehandlingssteknik, varav den digitala lämpade sig bättre. Dopplerbreddningen mättes med en hög-renlighetsgermaniumdetektor och en digital gammaspektrometer. Resultaten visar en minskning i S-parameter och en ökning i W-parameter med sjunkande temperatur, där förändringen i dessa är störst i ultralåga temperaturer. Detta beteende tolkas som ett resultat av ofullständig positrontermalisation. Livstidsresultaten är svårare att tolka, eftersom svårigheterna med anordningen ledde till imprecisa mätresultat. Trenden i resultaten tyder dock på att det inte sker några förändringar i positronlivstid i hela temperatureintervallet, i enlighet med tidigare forskning

Empfänger-basierte Kalibrierkette für spektrale Bestrahlungsstärke mittels durchstimmbarer Laser an der PTB

A completely detector-based traceability chain for spectral irradiance measurements, independent from the high-temperature blackbody radiator, has been developed at the Physikalisch-Technische Bundesanstalt (PTB). Thus a SI traceability of the spectral irradiance is obtained without any use of calculable radiant sources. At the Tunable Laser In Photometry (TULIP) setup of PTB, The absolute irradiance responsivity of a continuously scannable spectroradiometer is derived from the spectral responsivity of a silicon trap detector, traceable to the primary cryogenic radiometer of PTB. This spectroradiometer can subsequently be used to calibrate the spectral irradiance of photometric and radiometric sources. With this calibration chain the two commonly used calibration steps to measure the blackbody temperature using calibrated filter-radiometers are replaced by the single calibration of the responsivity of the spectroradiometer against a trap detector. At present, irradiance measurements of lamps in the spectral range between 565 nm and 975 nm were measured with expanded uncertainties lower than 1 %.Eine vollständig Empfänger-basierte Kalibrierkette für spektrale Bestrahlungsstärke, unabhängig von berechenbaren Strahlungsquellen wie z. B. den Hochtemperatur-Schwarzen-Strahler, wurde an der Physikalisch-Technischen Bundesanstalt (PTB) entwickelt. Am TULIP (Tunable Laser In Photometry)-Aufbau der PTB wird die absolute Bestrahlungsstärkeempfindlichkeit eines Spektroradiometers aus der spektralen Empfindlichkeit eines Silizium-Trap-Empfängers bestimmt, die wiederum auf das Primärnormal für spektale Empfindlichkeit der PTB, das Kryoradiometer, rückgeführt ist. Das so kalibrierte Spektroradiometer kann anschließend verwendet werden, um die spektrale Bestrahlungsstärke verschiedener photometrischer und radiometrischer Quellen zu bestimmen. Mit dieser Methode könnten die bisher notwendigen zwei Kalibrierschritte zur Bestimmung der Temperatur eines Schwarzen Strahlers ersetzt werden durch eine einzige Kalibrierung der Bestrahlungsstärkeempfindlichkeit eines Spektroradiometers gegen einen Trap-Empfänger. Derzeit wurden Messungen der Bestrahlungsstärke an Lampen im Spektralbereich zwischen 565 nm und 975 nm mit einer erweiterten Messunsicherheit von kleiner als 1 % durchgeführt

Predictable Quantum Efficient Detector

This thesis gives an overview of the Predictable Quantum Efficient Detector designed to measure optical radiation with theoretical relative uncertainty of 1 ppm (parts per million). The device is based on two custom made large area induced junction silicon photodiodes arranged in a wedged trap structure. High internal quantum efficiency (IQE) of the photodiodes is achieved by means of low doping concentration and usage of the reverse bias voltage. The IQE is predicted to be improved furthermore using low operating temperature close to 77 K. The losses due to reflected light are minimized by multiple reflections between the photodiodes. Low losses allow the PQED to work as an ideal quantum detector whose spectral responsivity is determined purely by the fundamental constants h, c, e and vacuum wavelength lambda. The remaining minor charge carrier losses are predictable using physical modelling whereas fractional reflectance losses can be measured. These properties classify the PQED as an absolute detector which does not require calibration against any other radiometric primary standard. The prototype PQED was compared against present primary standard - the cryogenic radiometer – at the wavelengths of 476 nm, 532 nm and 760 nm at room temperature and at liquid nitrogen temperature. Comparisons showed that the predicted external quantum deficiency of the PQED agreed with the measured external quantum deficiency within the expanded uncertainty of 60 ppm to 180 ppm determined by the cryogenic radiometer at both temperatures. These results indicate that the responsivity of the PQED is highly predictable and its uncertainty is comparable with the uncertainty of the conventional cryogenic radiometer. Such data provide evidence that the cryogenic radiometer operated close to 10 K temperatures may be replaced by a PQED operated even at room temperature. The advantage of the PQED is its simple operation which is comparable with any other silicon based photodetector whereas its optical radiation detection uncertainty is comparable with expensive and sophisticated cryogenic radiometer

Cryogenic scintillation properties of n-type GaAs for the direct detection of MeV/c2 dark matter

This paper is the first report of n-type GaAs as a cryogenic scintillation radiation detector for the detection of electron recoils from interacting dark matter (DM) particles in the poorly explored MeV/c2 mass range. Seven GaAs samples from two commercial suppliers and with different silicon and boron concentrations were studied for their low temperature optical and scintillation properties. All samples are n-type even at low temperatures and exhibit emission between silicon donors and boron acceptors that peaks at 1.33 eV (930 nm). The lowest excitation band peaks at 1.44 eV (860 nm), and the overlap between the emission and excitation bands is small. The X-ray excited luminosities range from 7 to 43 photons/keV. Thermally stimulated luminescence measurements show that n-type GaAs does not accumulate metastable radiative states that could cause afterglow. Further development and use with cryogenic photodetectors promises a remarkable combination of large target size, ultra-low backgrounds, and a sensitivity to electron recoils of a few eV that would be produced by DM particles as light as a few MeV/c2