Formation kinetics of copper-related light-induced degradation in crystalline silicon

Light-induced degradation (LID) is a deleterious effect in crystalline silicon, which is considered to originate from recombination-active boron-oxygen complexes and/or copper-related defects. Although LID in both cases appears as a fast initial decay followed by a second slower degradation, we show that the time constant of copper-related degradation increases with increasing boron concentration in contrast to boron-oxygen LID. Temperature-dependent analysis reveals that the defect formation is limited by copper diffusion. Finally, interface defect density measurements confirm that copper-related LID is dominated by recombination in the wafer bulk.Peer reviewe

Accelerated light-induced degradation for detecting copper contamination in p-type silicon

Copper is a harmful metal impurity that significantly impacts the performance of silicon-based devices if present in active regions. In this contribution, we propose a fast method consisting of simultaneous illumination and annealing for the detection of copper contamination in p-type silicon. Our results show that, within minutes, such method is capable of producing a significant reduction of the minority carrier lifetime. A spatial distribution map of copper contamination can then be obtained through the lifetime values measured before and after degradation. In order to separate the effect of the light-activated copper defects from the other metastable complexes in low resistivity Cz-silicon, we carried out a dark anneal at 200 C, which is known to fully recover the boron-oxygen defect. Similar to the boron-oxygen behavior, we show that the dark anneal also recovers the copper defects. However, the recovery is only partial and it can be used to identify the possible presence of copper contamination.Peer reviewe

Room-temperature method for minimizing light-induced degradation in crystalline silicon

Although light-induced degradation (LID) in crystalline silicon is attributed to the formation of boron-oxygen recombination centers, copper contamination of silicon has recently been observed to result in similar degradation. As positively charged interstitialcopper stays mobile at room temperature in silicon, we show that the bulk copper concentration can be reduced by depositing a large negative charge onto the wafer surface. Consequently, light-induced degradation is reduced significantly in both low- and high-resistivity boron-doped Czochralski-grown silicon.Peer reviewe

Reduction of Light-induced Degradation of Boron-doped Solar-grade Czochralski Silicon by Corona Charging

This study aims at the reduction of light-induced degradation of boron-doped solar-grade Czochralski silicon wafers by corona charging. The method consists of deposition of negative charges on both surface sides of wafer and keeping the wafer in dark for 24 hours to allow the diffusion of positively-charged interstitial copper towards the surfaces. This method proves to be useful to reduce or eliminate light-induced degradation caused by copper. The degradation was significantly reduced in both intentionally (copper-contaminated of the negative charge was found to be proportional to the reduction strengthPeer reviewe

Light-induced degradation in copper-contaminated gallium-doped silicon

To date, gallium-doped Czochralski (Cz) silicon has constituted a solar cell bulk material free of light-induced degradation. However, we measure light-induced degradation in gallium-doped Cz silicon in the presence of copper impurities. The measured degradation depends on the copper concentration and the material resistivity. Gallium-doped Cz silicon is found to be less sensitive to copper impurities than borondoped Cz silicon, emphasizing the role of boron in the formation of copper-related light-induced degradation.Peer reviewe

Experimental evidence on removing copper and light-induced degradation from silicon by negative charge

In addition to boron and oxygen, copper is also known to cause light-induced degradation (LID) in silicon. We have demonstrated previously that LID can be prevented by depositing negative corona charge onto the wafer surfaces. Positively charged interstitial copper ions are proposed to diffuse to the negatively charged surface and consequently empty the bulk of copper. In this study, copper out-diffusion was confirmed by chemical analysis of the near surface region of negatively/positively charged silicon wafer. Furthermore, LID was permanently removed by etching the copper-rich surface layer after negative charge deposition. These results demonstrate that (i) copper can be effectively removed from the bulk by negative charge, (ii) under illumination copper forms a recombination active defect in the bulk of the wafer causing severe light induced degradation.Peer reviewe

Cell-type-specific inhibition of the dendritic plateau potential in striatal spiny projection neurons

Striatal spiny projection neurons (SPNs) receive convergent excitatory synaptic inputs from the cortex and thalamus. Activation of spatially clustered and temporally synchronized excitatory inputs at the distal dendrites could trigger plateau potentials in SPNs. Such supralinear synaptic integration is crucial for dendritic computation. However, how plateau potentials interact with subsequent excitatory and inhibitory synaptic inputs remains unknown. By combining computational simulation, two-photon imaging, optogenetics, and dualcolor uncaging of glutamate and GABA, we demonstrate that plateau potentials can broaden the spatiotemporal window for integrating excitatory inputs and promote spiking. The temporal window of spiking can be delicately controlled by GABAergic inhibition in a celltype–specific manner. This subtle inhibitory control of plateau potential depends on the location and kinetics of the GABAergic inputs and is achieved by the balance between relief and reestablishment of NMDA receptor Mg2+ block. These findings represent a mechanism for controlling spatiotemporal synaptic integration in SPNs

Järngettering med aluminium och bakytspassivering av kristallina kiselsolceller

The purpose of this Master's thesis was to study aluminium gettering of iron impurities in single crystalline silicon. The intention was to determinate the iron segregation coefficient of aluminium segregation gettering at temperatures lower than 850°C. Hence, 20 nm of pure aluminium was sputtered onto the backside of 400 µm thick, 2.87 OMEGA -cm p-doped Czochralski silicon wafers, which had been intentionally iron contaminated to a level of (3.36 ± 0.14) x 1013cm-3. The iron concentration of the silicon wafer was measured through Surface Photovoltage (SPV) diffusion length measurements. Iron gettering with aluminium at temperatures 800 - 840°C reduced the initial iron concentration to the range 1010 - 1011 cm-3. Therefore, the iron segregation coefficient ranged from (5.28± 3.38) x 107 at 800°C to (5.23±2.48) x 105 at 840°C. The resulting high iron segregation coefficient also led to a large iron segregation enthalpy of 21.73 eV at 820 - 840°C. High temperature annealing of an aluminized crystalline silicon wafer also creates an aluminium back-surface field at the backside of the wafer. This back-surface field reduces the back-surface recombination and improves the solar cell efficiency together with the iron gettering. Hence, the back-surface recombination velocity of the aluminium back-surface field was also studied at 800, 850 and 900°C. In these experiments, 1 and 3.5 µm of pure aluminium was sputtered onto the back surface of clean 200 µm thick, 2.87 OMEGA -cm p-doped crystalline silicon wafers. The back-surface fields were formed by 30 min anneals and the diffusion lengths of the wafers were measured with Surface Photovoltage. The measurements resulted in back-surface recom bination velocities of (3.1+1x107-1.85) x 104 cm/s for 3.5 µm aluminium annealed at 850°C and (5.5+3.7-1.6) x 103 cm/s for 3.5 µm aluminium at 900°C. The 1 µm aluminium layer and the 3.5 µm layer annealed at 800°C did not reduce the back-surface recombination from its initial ohmic value 107 cm/s. The results confirmed the theoretical assumption that the recombination decreases as a function of increasing aluminium thickness and increasing formation temperature

Kopparrelaterad fotodegradering i kristallint kisel

Unintentional copper and nickel impurities are common in silicon-based devices due to the abundance of contamination sources in industrial silicon crystallization and wafer processing lines. High solubility and diffusivity result readily in significant impurity concentrations, which cause charge-carrier recombination and reduce the device response. This work confirms that nickel diffuses as fast as copper in silicon, emphasizing the importance of contamination control in silicon-based devices. Copper contamination is known to form recombination-active defects in silicon during illumination, which is observed as copper-related light-induced degradation (Cu-LID). In order to identify the  extent of degradation in silicon-based devices, this work focuses on determining the properties of Cu-LID in gallium-doped Czochralski (Cz) silicon, boron-doped Cz-Si, and boron-doped multicrystalline silicon. Cu-LID is determined to be predominantly a bulk recombination effect, and the formed defects are found to be stable at 200°C. Slower Cu-LID is observed in Ga-Si compared to B-Si, suggesting that Cu-LID formation is limited by the effective copper diffusivity. Cu-LID is shown to completely disappear after negative sample surface charging and illumination. The negative surface charge is achieved by corona charging or aluminum oxide deposition. Cu-LID removal is observed to have no impact on classical boron-oxygen-related light-induced degradation (BO-LID), which has previously been shown to recover at 200°C. Unlike BO-LID, the activation energy of Cu-LID is found to depend on the silicon doping concentration. Hence, Cu-LID and BO-LID are concluded to be two different degradation effects, which can occur simultaneously in silicon-based devices.Kiselbaserade elektroniska komponenter är ofta oavsiktligt förorenade av koppar och nickel från otaliga kontaminationskällor i industriella komponentframställningsprocesser. Metallernas höga diffusivitet samt löslighet leder fort till markanta orenhetskoncentrationer, vilka förorsakar rekombination av laddningsbärare och nedsatt komponentrespons. Denna avhandling bekräftar att nickel diffuserar lika fort som koppar i kristallint kisel, vilket betonar vikten av metallorenhetskontroll i kiselbaserade komponenter. Kopparorenheter förorsakar fotodegradadering (Cu-LID) i kisel via formationen av rekombinationsaktiva koppardefekter under illuminering. För att fastställa omfattningen av fotodegradadering i kiselbaserade komponenter, fokuserar denna avhandling på att identifiera egenskaper för Cu-LID i gallium-dopat Czochralski (Cz) kisel, boron-dopat Cz-Si och boron-dopat mångkristallint kisel. Cu-LID finnes orsaka främst bulkrekombination och de formade koppardefekterna är stabila i 200°C. Cu-LID sker långsammare i Ga-Si jämfört med B-Si, vilket antyder att fotodegraderingsprocessen begränsas av den effektiva koppardiffusiviteten. I avhandlingen förhindras kopparrelaterad fotodegradadering fullständigt genom att kombinera negativ kiselytladdning med illuminering. Den negativa ytladdningen skapas via deposition av koronaladdning eller aluminiumoxidtunnfilm. Avlägsning av Cu-LID inverkar inte på klassisk bor-syre-relaterad fotodegraderingen (BO-LID), som förekommer i kisel utan kopparföroreningar och försvinner i 200°C. I motsats till BO-LID beror aktiveringsenergin för Cu-LID på dopingkoncentrationen i kiselmaterialet. Följaktligen fastställs Cu-LID och BO-LID vara två skilda former av fotodegradering, vilka kan förkomma samtidigt i kiselbaserade elektroniska komponenter

Sällskapsdjur och grönväxter – en grönväxtguide för sällskapsdjursägare

Tämän opinnäytetyön tarkoituksena oli tehdä helppo ja informatiivinen opas lemmikinomistajille, jotka myös haluavat viherkasveja kotiinsa. Monet viherkasvit ovat myrkyllisiä lemmikeille omistajan tietämättä. Viherkasvit sekä lemmikit ovat molemmat hyvin suosittuja suomalaisessa kodissa. Ongelman lähtökohtana on se, miten ne kaksi saadaan sujuvasti samaan kotiin aiheuttamatta vaaratilanteita. Työssä tehtiin kaksi tutkimusta sekä haastateltiin eläinlääkäreitä. Tällä pyrittiin saamaan mahdollisimman laaja kuva siitä, miten myrkylliset viherkasvit vaikuttavat lemmikkeihimme. Olemme erikseen keskittyneet kolmeen eri lemmikkiin; koiraan, kissaan ja kaniin, joiden kasviherkyydestä kerromme tarkemmin. Työn lopputuloksena on suuntaa antava taulukko, josta voi nopeasti ja helposti tarkistaa tietyn viherkasvin mahdollisen myrkyllisyyden, ja myös myrkyllisyysasteen sekä oireet.Med detta examensarbete ville vi skapa en lätt och informativ guide för sällskapsdjursägare som också vill ha grönväxter i sitt hem. Många sällskapsdjursägare är omedvetna om att vissa grönväxter är giftiga för sällskapsdjur. Det är väldigt populärt i Finland att ha sällskapsdjur och grönväxter och problem kan uppstå då man vill kombinera de två förenämnda på ett säkert sätt. I vårt arbete gjorde vi två undersökningar och intervjuade flera veterinärer. Genom detta hoppades vi på att få en bra helhetsbild över vilka grönväxter som påverkar sällskapsdjur och om det är ett utbrett problem. Vi har koncentrerat oss på tre sällskapsdjur, hund, katt och kanin, vilka vi berättar mer noggrant om då det kommer till växtkänslighet. Arbetet resulterar i en tabell som lätt och smidigt berättar om vilka grönväxter som är giftiga för ditt sällskapsdjur. Giftighetsgraden nämns också i tabellen.With this bachelor’s thesis we wanted to make an easy and informative guide to pet-owners and plant-enthusiasts. Many houseplants are poisonous for pets without you knowing it. Houseplants and pets are both very popular in Finnish homes, but the problem that needs solving is how to combine these two in a safe way. We made two different studies and we also interviewed a few veterinaries. With these methods we tried to get an accurate picture of how poisonous plants affect our pets. We have concentrated on three pets: dogs, cats and rabbits. In the final product you will find an indicative table filled with information about plants that may harm your pet, also the degree of toxicity