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1

Optical properties of porous Si/PECVD SiNx:H reflector on single crystalline Si for solar cells

Remache L., Nychyporuk T., Guermit N., Fourmond E., Mahdjoub A., Lemiti M.

Materials Science Poland

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2016

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Vol. 34, No. 1

94--100

EN

The improvement of optical confinement on the back crystalline silicon solar cell is one of the factors leading to its better performance. Porous silicon (PS) layer can be used as a back reflector (BR) in solar cells. In this work, single layers of porous silicon were grown by electrodeposition on a single crystalline silicon substrate. The measurement of the total reflectivity (RT) on Si/PS surface showed a significant improvement in optical confinement compared to that measured on Si/standard Al back surface field (BSF). The internal reflectivity (RB) extracted from total reflectivity measurements achieved 86 % for the optimized single PS layer (92 nm thick layer with 60 % porosity) in the wavelength range between 950 and 1200 nm. This improvement was estimated as more than 17 % compared to that measured on the surface of Si/BSF Al contact. To improve the stability and passivation properties of PS layer BR, silicon nitride layer (SiNx) was deposited by PECVD on a PS layer. The maximum measured total reflectivity for PS/SiNx achieved approximately 56 % corresponding to an improved RB of up to 83 %. The PS formation process in combination with the PECVD SiNx, can be applied in the photovoltaic cell technology and offer a promising technique to produce high-efficiency and low-cost c-Si solar cells.

2

Wpływ tylnego lustra dielektrycznego na działanie krzemowych, cienkowarstwowych ogniw słonecznych otrzymanych metodą epitaksji z fazy gazowej

Cieślak K., Fave A., Lemiti M.

Czasopismo Inżynierii Lądowej, Środowiska i Architektury / Journal of Civil Engineering, Environment and Architecture

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2016

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z. 63, nr 4

71--77

PL

Metoda epitaksji z fazy gazowej została użyta do wytworzenia krzemowych, cienkowarstwowych ogniw słonecznych. Emiter wyprodukowanych ogniw fotowoltaicznych był typu p i znajdował się po tylnej stronie ogniwa, a absorberem był krzem typu n. W celu obniżenia kosztów produkcji aktywnej warstwy, został użyty dwuwarstwowy krzem porowaty wytworzony na krzemie monokrystalicznym. Krzem porowaty składał się z warstwy o wysokim stopniu porowatości oraz warstwy o niskim stopniu porowatości, obecnej na powierzchni. Takie rozwiązanie pozwala na wzrost monokrystalicznej warstwy o wysokiej jakości oraz na odczepienie jej od podłoża wzrostowego i ponowne jego użycie w kolejnym procesie wzrostu epitaksjalnego. Dodatkowo w celu zwiększenia odpowiedzi ogniw słonecznych na fale elektromagnetyczne w zakresie 700 nm – 1200 nm, zostało opracowane i naniesione lustro dielektryczne składające się z warstwy SiNx/SiOx lub pojedynczej warstwy SiNx. Warstwa aktywna wraz z naniesionym lustrem była podda badaniu na współczynnik odbicia światła o długości fali z w/w zakresu. W celach porównawczych zostały zbadane próbki z dwoma różnymi lustrami oraz próbka referencyjna bez lustra. Badania wykazały, że zastosowane lustro dielektryczne spełnia swoje zadanie i zwiększa współczynnik odbicia światła o ponad 70%. Oznacza to, że zastosowanie w/w lustra dielektrycznego będzie miało pozytywny wpływ na współczynnik absorpcji światła w ogniwie fotowoltaicznym, co będzie się bezpośrednio przekładało na jego parametry elektryczne.

EN

Vapor phase epitaxy (VPE) method was used to fabricate thin film silicon solar cells. Active layer was build with p type back side emitter, n type absorber and n+ type front surface field (FSF). In order to reduce costs of production double porous silicon structure was fabricated on a monocrystalline silicone. Porous silicon had a one low porosity layer on the top of a growth substrate and high porosity area just underneath the low porosity film. That kind of structure enabled to perform growth of a monocrystalline epitaxial silicon layer. During growth, the high porosity area was degraded due to a high temperature treatment and after the process detachment of an active layer was possible. After additional cleaning seed substrate can be reused in another VPE process. In order to increase spectral response of fabricated solar cells to low energy photons from a wavelength range 700 nm – 1200 nm, dielectric mirror was developed and deposited. Two structures were checked – double layer build with SiOx/SiNx and one layer of SiNx. Active layer grown by means of VPE with a dielectric mirror deposited was examined in order to establish reflectivity from a given structures. In order to make comparison, reference sample was fabricated. It had the same structure of an active layer but there was no dielectric mirror deposited. Analysis of the results showed that the dielectric mirror works as expected and reflectivity in a wavelength range 700 nm – 1200 nm, is more than 70% higher for the structure with the dielectric mirror compared to the reference sample. It means that proposed solution would increase the absorbance inside the material and would have a positive influence on the thin silicon solar cells performance.

3

Metoda otrzymywania monokrystalicznych folii krzemowych z wykorzystaniem krzemu porowatego

Sarnecki J., Brzozowski A., Lipiński D.

Materiały Elektroniczne

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2014

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T. 42, nr 1

24--31

PL

Określono warunki i opracowano metodę otrzymywania folii krzemowych o grubości do ~ 100 μm i wymiarach 50 x 50 mm. Metoda ta polega na odrywaniu warstw epitaksjalnych osadzanych na porowatej powierzchni płytki krzemowej typu p+. Opracowano oryginalną metodę odrywania warstwy epitaksjalnej łączącą działanie obniżonego ciśnienia i kąpieli w gorącej wodzie.

EN

A method of obtaining silicon foil with the thickness of up to 100 μm and dimensions 50 x 50 mm was worked out and experimental conditions were determined. This technique consists in the separation of epitaxial layers deposited on the porous surface of the p+ silicon wafer. Such an original method of epitaxial layer separation, combining the effect of low pressure and a bath in hot water, was developed.

4

Fabrication and Optoelectronic properties of Fluoride tin oxides/porous silicon/p-Silicon heterojunction

Hadi H. A.

International Letters of Chemistry, Physics and Astronomy

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2014

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Vol. 17, iss. 2

142--152

EN

In this paper, formation of a nanostructure semi transparence fluoride tin oxides (FTO) by spray pyrolysis technique on porous silicon PS layer. Porous silicon PS layer was prepared by anodization of p-type silicon wafers to fabricate of the UV- Visible Fluoride-doped tin oxide /Porous silicon /p-Si heterojunction photodetector. Optical properties of FTO thin films were measured. The optical band gap of 3.77 eV for SnO2 : F for film was deduced. From (I-V) and (C-V) measurements, the barrier ØB height for FTO/PS diode was of 0.77, and the built in voltage Vbi, which was of 0.95 V. External quantum efficiency was 55 % at 500 nm which corresponding to peak responsivity of 1.15 A/W at 1 V bias. The PS band gap in the vicinity of PS/c-Si heterojunction was 1.38 eV.

5

Sensors on the Basis of PorSi for MEMS

Lobur M., Kosobutskyy P., Naperalski A., Monastyrski L.

Machine Dynamics Research

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2013

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Vol. 37, No. 2

60-64

EN

We propose to use technology of electrochemical formation of low-dimensional porous silicon(porSi), which is compatible with the standard technologies of silicon VLSI, for creation of sensor part of MEMS "Lab-on-chip" type.

6

Fabrication and characterization of porous silicon layer prepared by photo-electrochemical etching in CH3OH:HF solution

Hadi H.A., Ismail R.A., Habubi N.F.

International Letters of Chemistry, Physics and Astronomy

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2013

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Vol. 3

29-36

EN

Porous silicon (PS) has been fabricated by Photo-electrochemical etching. Porous silicon was anodized on n-type Si in light using a current density of 20mA/cm2 for 10 min. The porous structure formation was confirmed using XRD and AFM studies. The root mean square (RMS) roughness of the Porous silicon layer is found to be around 47.5 nm and the ten point height was 317 nm. The average of pores diameter was 419.98nm, and the grain growth is columnar with a (211) preferred orientation. The grain size of the PS was estimated from the Scherer's formula and found to be 73 nm. All the properties of the porous silicon layer, such as porosity and the thickness depend on the anodization parameters. The porosity (P) was approximately 77 %. The thickness of the layer formed during an anodization in constant current was 3.54nm in gravimetric method, while its value was 1.77nm by using the theoretical relation.

7

Krzemowe warstwy epitaksjalne do zastosowań fotowoltaicznych osadzane na krzemie porowatym

Lipiński D., Sarnecki J., Brzozowski A., Mazur K.

Materiały Elektroniczne

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2012

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T. 40, nr 3

28-37

PL

Ustalono warunki wytwarzania warstw o odpowiedniej porowatości zapewniającej osadzanie w procesie epitaksji z fazy gazowej warstw krzemowych o grubości powyżej 50 μm. W zależności od rezystywności płytek krzemowych typu p+ o orientacji <111> oraz <100> określono związek między gęstością prądu trawienia elektrochemicznego, a porowatością wytworzonych warstw porowatych. Otrzymano warstwy porowate z porowatością w zakresie 5 % - 70 %. Ustalono parametry procesu epitaksji i osadzono krzemowe warstwy epitaksjalne o wysokiej perfekcji strukturalnej i zakładanych parametrach elektrycznych.

EN

The conditions for producing layers with proper porosity that allows epitaxial growth of Si layers with the thickness of about 50 μm have been established. The relationship between the layer porosity, current density and substrate resistivity has been determined. The layers with porosity in the range between 5 % and 70 % have been obtained. The parameters of the CVD process have been established. Epitaxial silicon layers of high structural perfection and required electrical parameters have been obtained, which has been confirmed by the XRD and SR measurements as well as SEM observations.

8

Porous silicon : obtainig, properties and applications

Craciunoiu F., Miu M.

Elektronika : konstrukcje, technologie, zastosowania

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2011

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Vol. 52, nr 8

24-27

EN

Silicon wafer during electrochemical etching process is changed into a sponge structure named porous silicon. Porous silicon due to the well-developed surface area can be used in many applications. The present paper tries to review some of our recent results related to porous silicon, a special attention being dedicated using it as the substrate for cold field emitters.

PL

W czasie trawienia elektrochemicznego płytka krzemu jest przekształcana w strukturę typu gąbka zwaną porowatym krzemem. Porowaty krzem z powodu dobrze rozwiniętej powierzchni właściwej może być stosowany w wielu aplikacjach. W artykule przedstawiono wyniki ostatnich badań wykonanych w IMT-Bucharest, dotyczących porowatego krzemu, zwłaszcza jego zastosowania jako podłoża dla emiterów polowych.

9

Temperature measurement using a Chx/porous silicon/Si structure encapsulated in a CO2 rich environment

Chiali A., Ghellai N., Gabouze N., Sari N.

Advances in Materials Science

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2010

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Vol. 10, nr 2(24)

4-10

EN

This work reports on the possible use of microporous silicon as a temperature sensor. This work is based on previous published works [7, 8, and 9]. The device is based on hydrocarbon group (CHx) / porous silicon (PS) /Si structure. The porous sample was coated with hydrocarbons groups deposited by the plasma of methane /argon mixture. Current–voltage characteristics have been investigated as a function of temperature in the range 200C-70°C.The results show that for a constant voltage in the range 0.7-1V, the current increases linearly with the environment temperature reaches a maximum at 70°C and then stabilizes. This result suggests that the developed structure can be used for sensing temperatures not exceeding 70°C.

10

Liquid crystal monolayers on silicon surface

Szeląg A., Trybała A., Stańczyk W.

Polish Journal of Applied Chemistry

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2009

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Vol. 53, nr 1

93-99

EN

Surface Organometallic Chemistry (SOMC) methods have been applied, for the first time, in synthesis of liquid crystalline (LC) layers on silicon wafer surface. We have obtained unique materials with modified semiconductor (Si) surface, which can be applied in opto-electronics as switching and coupling devices as well as orienting optical elements in liquid crystalline cells. The covalently bonded LC monolayers can orient low molecular weight LC thin films up to -10 |im thickness. They are expected to be used primarily as a novel type of couplers and routers in laser telecommunication technology. The evaluation of the most effective analytical methods is also presented.

11

A study of the gas specificity of porous silicon sensors for organic vapours

Choi S. H., Cheng H., Park S. H., Kim H. J., Kim Y. Y., Lee K. W.

Materials Science Poland

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2009

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Vol. 27, No. 2

603--610

EN

A porous silicon sensor was investigated as a means to determine the response specificity for organic vapours. Porous silicon layers were fabricated by electrochemical anodization of p-type crystalline silicon in an HF ethanol solution under various conditions. The porous silicon sensors were placed in a gas chamber with various organic vapours, and the changes in electrical resistance under constant voltage of each sensor were used as detection signals. The sensors recorded various changes in resistivity for various organic vapours.

12

Micro- and nanostructurization of surfaces - techniques and applications

Górecka-Drzazga A.

Optica Applicata

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2007

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Vol. 37, nr 4

341-357

EN

In the paper some surface structurization methods are presented. Wet and/or dry etching, and thermal oxidation process have been used to form arrays of gated and non-gated sharp silicon microtips on a silicon wafer. A transfer mold technique (mold) has been applied to produce arrays of silicon carbide (SiC) microtips located on a glass wafer. The surface of the fabricated arrays has been also modificated by thin film metal layers and carbon nanotubes. Current-voltage characteristics of electron sources with a cold cathode build on the base of microtips arrays are presented. A new application of silicon microtips arrays for biochemistry is shown. The process of electrochemical etching of silicon has been used to form porous silicon and porous silicon dioxide layers. Applications of the porous layers for chemical and biochemical analyses are presented. Microstructurized surfaces modificated by carbon nanotubes have been used to improve the field emission characteristics of electron sources, and to obtain a miniature light source.

13

Novel gas sensor based on porous silicon measured by photovoltage, photoluminescence, and admittance spectroscopy

Bratkowski A., Korcala A., Łukasiak Z., Borowski P., Bała W.

Opto-Electronics Review

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2005

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Vol. 13, No. 1

35--38

EN

Porous silicon (PSi) layer as gas sensor, based on the change in photoconductivity, photoluminescence and admittance has been presented. PSi layer was prepared by electrochemical dissolution of p-type silicon wafer in HF. Photovoltage curves, photoluminescence spectra (PL) and admittance spectra have been measured in different gas concentrations. Photoconductivity (PC) spectra in vacuum and different gas atmosphere have been compared. Changes of photovoltage intensity curves and change of PC spectra versus concentration of vapour have been observed.

14

Porous surface silicon layers in silicon solar cells

Panek P., Dutkiewicz J., Levy-Clement C., Lipiński M., Bielańska E., Wodnicka K.

Archives of Metallurgy and Materials

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2005

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Vol. 50, iss. 2

417-421

EN

The porous silicon (PSi) layers have been studied in the aspect of their application in the multicrystalline silicon (mc-Si) solar cells. The macroporous layers were prepared by double-step chemical etching prior to the donor diffusion. They have been investigated using scanning (SEM) and transmission (TEM) electron microscopy to reveal the morphology of PSi layers. The techniques of spectral response and current-voltage characteristics have been used to determine the opto-electrical parameters of the solar cells. The porosity was measured by the mercury porosimetry and nitrogen sorption method. The porous layers reported here have had a sponge-like homogeneous structure over the whole 25 cm2 surface of each sample and the decreased effective reflectance (Reff) below 10%. As a final result the mc-Si solar cells with PSi layer were obtained with the conversion effciency (Eff) over 13%.

PL

W pracy przedstawiono metodę uzyskania redukcji odbicia fektywnego ( Eeff) poniżej 10% od powierzchni krzemu multikrystalicznego ( mc-Si ) dla promieniowania w zakresie 400÷1100 nm długości fali. Metoda polega na chemicznym trawieniu powierzchni mc-Si w roztworach na bazie HNO3:HF i wytworzeniu powierzchniowej tekstury geometrycznej w formie porów o średnicy od 30÷800 nm i porownywalnej głębokości. Krzem multikrystaliczny z warstwami krzemu porowatego wykorzystano do wytworzenia ogniw słonecznych. W zależnosci od wielkości porów otrzymano ogniwa o sprawności konwersji fotowoltaicznej od 9.8% do 13.0%.

15

Optical and microstructural properties of granded porous silicon layer

Lipiński M., Czternastek H., Sokołowski M., Panek P.

Archives of Metallurgy and Materials

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2005

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Vol. 50, iss. 2

387-393

EN

In this work we present the results of investigations of porous silicon (PS) layers for solar cells application. The PS was formed by chemical etching (stain etching) of n+-p Si substrate in a solution of HF, HNO3 and H2O. The dielectric response of a PS layer was modeled using a Bruggeman effective-medium approximation. It was shown that PS layer could be described by a model of graded layer with effective optical constants n(eff) and k(ef f) changing from these of bulk material (silicon) to these of surrounding (air). The porosity of the PS layer changed from 10% near the bulk silicon region to nearly 85% at the silicon-air interface. The effective reflectance of Cz-Si surface decreased to about 5% after PS layer formation.

PL

Przedstawiono wyniki badań własności optycznych i mikrostrukturalnych gradientowej warstwy z porowatego krzemu naniesionej metodą chamicznego trawienia. Podłożem były płytki polerowanego krzemu typu p z uformowanym złaczem n+-p. Do symulacji własności wynikających z istniejącego gradientu założono wielowarstwową strukturę porowatego krzemu stosując przybliżenie Bruggeman’a efektywnego ośrodka. Określono wartości współczynnika załamania i ekstynkcji (neff i keff) w warstwie porowatego krzemu w funkcji długosci fali światła oraz odległoćci od powierzchni krzemowego podłoża. Porowatość zmieniała się w granicach od 10% w pobliżu granicy podłoże-krzem porowaty do około 85% na granicy krzem porowaty-powietrze. Efektywny współczynnik odbicia dle krzemu z naniesiona warstwa porowatego krzemu wynosił tylko 5% w porównaniu z 25% wartoscią współczynnika odbicia od steksturyzowanej w KOH powierzchni multikrystalicznego krzemu.

16

Morphology of silicon (111) during electrochemical etching in NH4F electrolytes

Jakubowicz J.

Advances in Materials Science

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2005

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Vol. 5, nr 1-3

49-54

EN

The n-type silicon with (111) orientation and resistivity of 8-12 .źcm was electrochemically etched. The results obtained by electrochemical etching of silicon in 0.1M NH4F (pH4.5), 0.1M NH4F (pH4.0) and 0.2M NH4F (pH4.0) electrolytes, indicates that slight increase of the NH4F concentration by 0.1M results in faster silicon dissolution. In slightly reactive 0.1M NH4F (pH4.5), we can observe initial stage of silicon dissolution on the inside edges of atomic terraces. Flat atomic terrace under electrochemical etching undergoes to mesa-type structures surrounded by strongly corrugated areas. The diameter and heights of the mesas are 150-200 nm and 5-7 nm, respectively. The mesa-type structures are the remnants of the atomic terraces and theirs formation proceed independently on the electrolyte concentration. The mesas appear faster at higher concentration and faster disappear by pits formation. During increase of etching time, increase of pore size, more in the case of diameter than depth, because pits coagulation appears.

17

Effect of macroporous silicon layer on opto-electrical parameters of multicrystalline silicon solar cells

Panek P.

Opto-Electronics Review

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2004

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Vol. 12, No. 1

45--48

EN

The feasibility of improvement in multicrystalline silicon (mc-Si) solar cells is considered by applying porous silicon (PSi) layers obtained and modified with chemical double-step method. PSi layers have a different diameter of pores which determines electrical and optical characteristics of solar cells. Structural properties of these layers were investigated by means of scanning electron microscopy. The reflectance, internal quantum efficiency, and current-voltage characteristics of the silicon solar cells with porous layers are reported. The PC1D computer program was applied to calculate the correlation between texture slope angle and electrical parameters of the solar cell. The diffusion results are also demonstrated using POCl3 as a donors source in an emitter with a sheet resistance in the range 30–80 Ω) which depends on a structure of the porous layer prepared before a diffusion process. Some technological problems using PSi in a solar cell structure and correlation between porous layer morphology and opto-electrical parameters are discussed. As a result, the mc-Si solar cell with 12.74% efficiency was obtained. We think that macroporous silicon formation process can be applied in industry technology that allows for exceeding efficiency limit of the mc-Si solar cells with TiOx, at the level of 13% at present.

18

Badanie transportu nośników w niedomieszkowanym krzemie porowatym metodą niestacjonarnego fotoprzewodnictwa

Bratkowski A., Łukasiak Z., Korcala A., Borowski P., Bała W.

Elektronika : konstrukcje, technologie, zastosowania

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2004

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Vol. 45, nr 10

15-16

PL

Warstwy krzemu porowatego otrzymano metodą elektochemicznej anodyzacji krzemu typu p. Wykonano pomiary krzemu typu p. Wykonano pomiary przebiegów czasowych fotonapięcia dla różnych długości fal światła wzbudzającego w różnych temperaturach. Pomiary pozwoliły wyznaczyć ruchliwość nośników prądu oraz określić energię głębokich poziomów w strukturze krzemu porowatego.

EN

Porous silicon layers were produced by electrochemical anodisation method. Photocurrent curves at different wavelength of excitation, temperatures and polarization voltages have been measured. Mobility of carriers and deep level energies were determined from photovoltage curves.

19

Kinetics of photoluminescence of porous silicon studied by photo-luminescence excitation spectroscopy and time-resolved spectroscopy

Łukasiak Z., Dalasiński P., Bała W.

Opto-Electronics Review

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2003

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Vol. 11, No. 2

113-117

EN

Photoluminescence (PL) spectra and excitation spectra (PLE) (under steady-state conditions), time resolved spectra (PL-TRS) and decay curves of photoluminescence (PL-DC) in micro- and nanosecond range (under pulsed operation) at different temperatures (10 K-room) on anodically etched boron–doped silicon are presented. PLE shows that visible PL is excited by light from UV region. PL and PL-TRS exhibit multiband structure and can be decomposed as a sum of few Gaussians. PL-DCs have multiexponential shape. Relaxation times depend on wavelength of the observation. To explain our results we assumed a model in which the multibarrier structure is formed by larger Si crystallites or wires (quantum well) surrounded by Si crystallites with diameters in the nanometer range (barrier region). The visible photoluminescence originates from radiative recombination between discrete energy levels in a quantum well

20

Krzywe prądowo-napięciowe a formowanie porowatej struktury w n-Si (111)

Jakubowicz J.

Inżynieria Materiałowa

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2003

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R. XXIV, nr 1

35--38

PL

Zbadano wpływ reaktywności rozcieńczonego elektrolitu NH4F o różnej molarności i pH na krzywe prądowo-napięciowe i zakres formowania porowatego krzemu. Obróbce elektrochemicznej w rosnącym potencjale poddano krzem monokrystaliczny typu n-Si (111). Przed obróbką elektrochemiczną zastosowano obróbkę chemiczną mającą na celu przygotowanie powierzchni o wysokiej jakości, zbudowanej z tarasów atomowych o szerokości 100/150 nm i wysokości 0,314 nm. Zmiany struktury określono z wykorzystaniem mikroskopu AFM. Wzrost reaktywności wpływa na rozszerzenie potencjałów, w których formowane są pory. Określono, iż większy wpływ wywiera molarność niż kwasowość. W wyniku wzrostu potencjału, z potencjału resztkowego do potencjału, w którym występuje maksymalna gęstość prądu, w krzemie pojawiają się pory o średnicy poniżej 80 nm i głębokości do 12 nm.

EN

Current-voltage characteristics in aspect of porous silicon formation has been investigated in diluted NH4F electrolytes with different molarity and pH. Electrochemical conditioning was done at increasing potential. Monocrystalline n-Si (111) wafers has been investigated. Before electrochemistry experiments chemical cleaning results in high quality surface composed from atomic terraces 100/150 nm wide and 0,314 nm high. The change in surface structure was investigated by AFM. A correlation between different anodisation parameters is done. It was found that molarity is more important than pH of the electrolyte. The potential range of porous silicon formation is extended for higher molarity. When the potential increases from the rest potential to the potential, where the maximum current occurs, in silicon wafer pores appear. The diameter of initial pores estimated to be below 80 nm and depth of pores approach to 12 nm.