Physical mechanisms of boron diffusion gettering of iron in silicon

We have studied the boron diffusion gettering (BDG) of iron in single crystalline silicon. The results show that iron is gettered efficiently by electrically inactive boron, which leads to gettering efficiencies comparable to phosphorus diffusion gettering (PDG). In addition we discuss the different physical mechanisms behind BDG. We also consider the possibilities of using boron diffusion gettering in solar cell fabrication and discuss the role of boron and iron concentration in the optimization of gettering efficiency.Peer reviewe

Ohjeistus sosiaaliseen mediaan matkailuyritykselle

Opinnäytetyö tutki kuinka suomalainen matkailuyritys voi hyödyntää sosiaalista mediaa markkinointikanavana. Työn toimeksiantaja on Fintravel Tour Operators Oy Rovaniemeltä. Työn ensisijainen kehittämistehtävä oli kehittää yrityksen sosiaalisen median käyttöä ja toissijainen kehittämistehtävä oli tutkia kuinka tavoittaa venäjänkielisiä matkustajia sosiaalisessa mediassa. Opinnäytetyö on toiminnallinen, mutta se sisältää myös laadullisen tutkimuksen piirteitä kahden henkilöhaastattelun muodossa. Haastateltavat olivat venäjänkielisen matkailualan ja sosiaalisen median asiantuntijoita. Haastattelut nauhoitettiin, litteroitiin ja analysoitiin. Tietoperustana toimivat digitaalinen media, matkailuala, sosiaalisen median strategiat pienille ja keskisuurille yrityksillä matkailualalla sekä venäjänkielisten Internet-käyttäytyminen. Tuotoksena kehitettiin ohjeistus sosiaalisen median toimintaa varten. Opinnäytetyön tulokset osoittavat, että oikein käytettynä sosiaalinen media voi olla hyödyllinen ja kustannustehokas markkinointikanava. Tärkeintä sosiaalisessa mediassa toimimisessa ovat aktiivinen osallistuminen, läsnäolo ja säännöllinen kohderyhmää kiinnostavan sisällön tuottaminen ja julkaiseminen. Lisäksi markkinointi sosiaalisessa mediassa tulee olla integroitu yrityksen muuhun markkinointiin. Matkailijat etsivät yhä enemmän matkailuun liittyvää tietoa Internetistä, eivätkä venäjänkieliset ole tässä suhteessa poikkeus, mutta he pidättäytyvät mielellään venäjänkielisissä palveluissa, kuten VKontakte tai Odnoklassniki. Myös Facebookin kaltaiset kansainväliset palvelut kasvattavat suosiotaan, erityisesti varakkaamman ja paremmin koulutetun väestön keskuudessa.This thesis examined how a Finnish travel company should take advantage of social media as a marketing channel. Employer of the study is Fintravel Tour Operators Oy, a travel agency from Rovaniemi. The primary objective of the study was to develop company’s social media usage and the secondary objective was to research how to reach Russian speaking travelers by social media. The thesis is a functional study but it includes also qualitative method in the form of two personal interviews from marketing specialists with knowledge and experience with Russian tourism industry and social media. Interviews were recorded, transcribed and analyzed. The theory background contains the examination of digital media in general, tourism industry, social media strategies for small and medium sized companies in the terms of tourism industry, and Internet behavior of Russian speaking population. Instructions for social media activities were developed as an product of the thesis. According to the thesis results social media can be valuable and cost-effective marketing chan-nel. The most important issues in social media are involvement, attendance and active content production and publishing. Marketing in social media must be integrated to company’s other mar-keting. Tourists increasingly search the web for travel-related information and Russian speakers are no exception, but they tend to stick to Russian websites such as VKontakte or Od-noklassniki. Also international services such as Facebook are gaining popularity, especially among the more wealthy and educated Russians in the big cities

Modeling boron diffusion gettering of iron in silicon solar cells

In this paper, a model is presented for boron diffusion gettering of iron in silicon during thermal processing. In the model, both the segregation of iron due to high boron doping concentration and heterogeneous precipitation of iron to the surface of the wafer are taken into account. It is shown, by comparing simulated results with experimental ones, that this model can be used to estimate boron diffusion gettering efficiency of iron under a variety of processing conditions. Finally, the application of the model to phosphorus diffusion gettering is discussed.Peer reviewe

Role of copper in light induced minority-carrier lifetime degradation of silicon

We investigate the impact of copper on the light induced minority-carrier lifetime degradation in various crystalline silicon materials. We demonstrate here that the presence of neither boron nor oxygen is necessary for the degradation effect. In addition, our experiments reveal that copper contamination alone can cause the light induced minority-carrier lifetime degradation.Peer reviewe

Gettering of Iron in Silicon Solar Cells With Implanted Emitters

We present here experimental results on the gettering of iron in Czochralski-grown silicon by phosphorus implantation. The gettering efficiency and the gettering mechanisms in a high resistivity implanted emitter are determined as a function of both initial iron level and gettering anneal. The results show that gettering in implanted emitters can be efficient if precipitation at the emitter is activated. This requires low gettering temperatures and/or high initial contamination level. The fastest method to getter iron from the bulk is to rapidly nucleate iron precipitates before the gettering anneal. Here, this was achieved by a fast ramp to the room temperature in between the implantation anneal and the gettering anneal.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

Phosphorus and boron diffusion gettering of iron in monocrystalline silicon

We have studied experimentally the phosphorus diffusion gettering (PDG) of iron in monocrystalline silicon at the temperature range of 650–800 °C. Our results fill the lack of data at low temperatures so that we can obtain a reliable segregation coefficient for iron between a phosphorus diffused layer and bulk silicon. The improved segregation coefficient is verified by time dependent PDG simulations. Comparison of the PDG to boron diffusion gettering (BDG) in the same temperature range shows PDG to be only slightly more effective than BDG. In general, we found that BDG requires more carefully designed processing conditions than PDG to reach a high gettering efficiency.Peer reviewe

Impact of phosphorus gettering parameters and initial iron level on silicon solar cell properties

We have studied experimentally the effect of different initial iron contamination levels on the electrical device properties of p-type Czochralski-silicon solar cells. By systematically varying phosphorus diffusion gettering (PDG) parameters, we demonstrate a strong correlation between the open-circuit voltage (Voc) and the gettering efficiency. Similar correlation is also obtained for the short-circuit current (Jsc), but phosphorus dependency somewhat complicates the interpretation: the higher the phosphorus content not only the better the gettering efficiency but also the stronger the emitter recombination. With initial bulk iron concentration as high as 2 × 1014 cm−3, conversion efficiencies comparable with non-contaminated cells were obtained, which demonstrates the enormous potential of PDG. The results also clearly reveal the importance of well-designed PDG: to achieve best results, the gettering parameters used for high purity silicon should be chosen differently as compared with for a material with high impurity content. Finally we discuss the possibility of achieving efficient gettering without deteriorating the emitter performance by combining a selective emitter with a PDG treatment.Peer reviewe

Modeling the effect of mobile ion contamination on the stability of a microelectromechanical resonator

We present a theoretical model for mobile ion contamination in a silicon microelectromechanical resonator. In the model both drift and diffusion of the mobile charge in dielectric films are taken into account. The model is verified through a comparison to existing experimental data. We show that the model can describe the frequency drift of resonators in a wide temperature range.Peer reviewe

Enhanced performance in the deteriorated area of multicrystalline silicon wafers by internal gettering

The deteriorated area of the multicrystalline silicon (mc-Si) ingots grown by directional solidification, commonly known as the Red Zone, is usually removed before wafering. This area, characterized by poor minority carrier lifetime, is located on the sides, at the top, and the bottom of the mc-Si ingots. In this study, the effect of internal gettering by oxygen precipitates and structural defects has been investigated on the bottom zone of a mc-Si ingot. Nucleation and growth of oxygen precipitates as well as low temperature annealing were studied. Photoluminescence imaging, lifetime mapping, and interstitial iron measurements performed by μ-PCD reveal a considerable reduction of the bottom Red Zone. An improvement of lifetime from below 1 µs to about 20 µs and a reduction of interstitial iron concentration from 1.32 × 1013 at/cm3 to 8.4 × 1010 at/cm3 are demonstrated in this paper.Peer reviewe