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Mechanism of P-n Junction Formation in Intrinsic Semiconductor by Laser Radiation
No full textI. INTRODUCTION
P-n junction is the most important component of many
semiconductor devices. Thermodiffusion, ion implantation and
molecular beam epitaxy are only a few methods to form a p-n
junction. The main drawback for these methods is high cost of
equipment. Therefore this equipment is not available for small
and medium companies. A possibility of p-n junction
formation by laser radiation was shown in several
semiconductors: p-Si, p-CdTe, p-InSb, p-InAs, p-PbSe and p-
Ge. Different mechanisms have been proposed to explain the
nature of inversion of conductivity type: impurities’
segregation, defects’ generation, amorphization and oxygen
related donor generation. However, the proposed mechanisms
have many flaws and even contradictions; therefore the
mechanism of p-n junction formation by laser radiation (LR)
is not clear until now. The aim of the work is to show a new
possibility of p-n junction formation in intrinsic elementary
semiconductor by LR without any impurities and to propose
the new mechanism of p-n junction formation.
II. RESULTS AND DISCUSSION
We assume that, the intrinsic defects play the main role in
formation of p-n junction. For this reason i-Ge crystal was
irradiated by Nd:YAG laser with different energy of quantum.
In experiments i-Ge single crystals with NA = 7.4 × 1011 cm-3
and ND = 6.8 × 1011 cm-3 s were used. Samples were prepared
by mechanical polishing with diamond grease followed by
chemical treatment with CP-4 etching solution. To form a p-n
junction, nanosecond Nd:YAG laser with wavelengths λ1 =
1064 nm, λ2= 532 nm and λ3= 266 was used. Measurements of
I-V characteristics were done by soldering 99% Sn and 1% Sb
alloy electrical contacts directly on the irradiated surface of i-
Ge and the opposite side. I-V characteristics of i-Ge samples
before and after irradiation different intensities of Nd:YAG
laser with wavelength 266 nm and different laser intensities
are shown in Fig.1.
Increase of rectification ratio (RR) of I-V characteristics
with intensity of the laser radiation, energy of laser radiation
quanta and numbers of pulses were observed in this
experiment (see Fig.2). Moreover, this process takes place in
threshold manner, it means, RR is non-monotonic function on
laser radiation intensity. These results are explained by
damage of p-n junction at threshold intensity (Ith) due to
formation of nanocones.The mechanism of this phenomenon is explained by
generation and redistribution of intrinsic point defects in
temperature gradient field, which causes strongly absorbed
LR. The redistribution of defects takes place because
interstitial atoms drift towards the irradiated surface, but
vacancies drift in the opposite direction – in the bulk of
semiconductor according to Thermogradient effect [1]. Since
interstitials in Ge crystal are of n-type and vacancies are
known to be of p-type [2], a p-n junction is formed.
III. CONCLUSIONS
For the first time we have proved that the mechanism of pn
junction formation in semiconductor is caused by generation
and redistribution of intrinsic point defects in temperature
gradient field induced by LR. Increase of rectification ratio of
p-n junction with the increase of LR intensity is typical for
Thermogradient effect; therefore this effect has the main role
in p-n junction formation.
IV. REFERENCES
[1] A. Medvid: Redistribution of Point Defects in the Crystalline Lattice of a
Semiconductor in an Inhomogeneous Temperature Field, Defect and
Diffusion Forum , 2002, 210-212: 89-102.
[2] Cor Claeys: Germanium-based technologies: from materials to devices.
London Elsevier B.V. 2007
Acknowledgment: The author gratefully acknowledges financial
support in part by the European Regional Development Fund within
the project “Sol-gel and laser technologies for the development of
nanostructures and barrier structures» No
2010/0221/2DP/2.1.1.1.0/10/APIA/VIAA/14
Improvement of CdZnTe Crystal Quality by Laser Radiation
No full textI. INTRODUCTION
Cadmium zinc telluride (CdZnTe) semiconductor crystals
have been shown to be the most promising materials for x-ray
and γ-ray detection [1, 2]. However, the yield of high quality
crystal is still limited by some important problems. Several
researchers have shown a possibility to improve crystal quality
by CO2 laser irradiation [3, 4]. This method has disadvantages,
such as long processing time, about 100 h, and damage of
crystal surface. The improvement of the quality of CdZnTe
crystal was observed after irradiation by Nd:YAG laser with
3.6×104 pulses. The leakage current of CdZnTe detector
decreases by 40%. The enhancement of energy resolution of
CdZnTe detector, especially at low energies, takes place after
irradiation by the laser. This effect is explained by small
defect precipitation on to Telluride (Te) inclusion due to
thermogradient effect around it.
II. EXPERIMENTS AND DISCUSSION
In this research CdZnTe crystal is grown by vertical
gradient freezing method using the high-purity Cd, Zn and Te:
7N materials and doping with 3 ppm of Indium characterized
by high concentration of non-controllable impurities and Te
inclusion is used.
Shallow impurities have strong influence on electrical
conductivity of semiconductor and leakage current of radiation
detector. Infrared transmission microscopy was used to
characterize CdZnTe samples, particularly concentration of Te
inclusions. Single crystals Cd1-xZnxTe have been irradiated by
the Nd:YAG laser with the following parameters: wavelength
λ = 1064 nm, pulse duration =3 ns, intensity 6.6 MW/cm2.
Treatment by laser was carried out at room temperature and
atmospheric pressure. CdZnTe samples were irradiated Nd:YAG laser and afterwards current voltage (I-V)
characteristic measurements were performed. I-V
characteristic measurements showed that sample resistivity is
rising after irradiation by 3.6×104 laser pulses and the dark
current is decreasing by 40%.After reaching specific number of pulses, saturation effect
can be observed. It means that no more changes of CdZnTe
sample resistivity were observed. FTIR spectra of CdZnTe
showed that after irradiation by the laser transparency of the
crystal is increased (Fig.1). To characterize sample as
radiation detector γ-ray spectroscopy measurement was used.
Measurements of γ-ray spectroscopy of CdZnTe crystal
irradiated by the laser have shown the improvement of the
energy spectral resolution (Fig.2). It can be concluded the
quality of CdZnTe crystal is improved.
III. CONCLUSIONS
1. The possibility to increase of Cd0.9Zn0.1Te crystal quality
after irradiation by Nd:YAG laser was shown.
2. Improvement of CdZnTe crystal quality is explained by
segregation of defects on to Te inclusion due to gradient of
temperature around it.
IV. REFERENCES
[1] T.E. Schlesinger, et all. Cadmium zinc telluride and its use as a nuclear
radiation detector material. Materials Science and Engineering: R:
Reports, 32(4/5) (2001), pp.103-189.
[2] F. Lebrun. Semiconductor detectors for soft gamma-ray astrophysics.
Nuclear Instruments & Methods in Physics Research Section, 563(1)
(2006), pp.200-204.
[3] M. Meier, M.J. Harrison, S. Spalsbury, D.S. McGregor. Laser-induced
thermomigration of Te precipitates in CdZnTe crystals. Journal of Growth. 311(2009), pp.4247-4250.
[4] S.V. Plyatsko, L.V. Rashkovetskyi. Laser-stimulated compensation of
volume defects in p-CdZnTe. Semiconductors, 40, (2006), pp.287-295
Applications of Informatics and Cybernetics in Compact Solar Combisystem for Multifamily Residential Buildings
No full textsystem and the analysis of a demonstration project. The solar
thermal system has been developed by three industrial partners
working in cooperation with Riga Technical University. The
industrial partners joined their forces to develop a new product,
which could benefit their core business. The basic product idea
is a solar thermal system coupled with a wood pellet system.
This is a 100% renewable energy solution for space heating and
domestic hot water in multifamily buildings. The system is
compact and factory assembled in a standard shipping container.
However, potential for optimization both exists for increasing
solar fraction and for reducing parasitic electricity demand.
The first part of the paper describes the system concept and
design, and the methodology proposed for the identification of
an optimized set of operating parameters based on informatics,
cybernetics and dynamic simulation.
The second part of the paper shows a case study where the
proposed optimization methodology is used for the optimization
of a demonstration project implemented in Latvia
Building Information Systems for Sustainable Construction
No full textThe importance of construction in the national socioeconomic
development is obvious. It affects both the life of an
individual and society as a whole as well as the environment
and the natural ecological balance. It creates a logistical base
in other economic sectors and describes economic
development and culture of the country.
Since the early 1990s, sustainable construction has been
widely accepted in the construction industry all around the
world. Building houses to meet the present need, we must take
care of not compromising the ability of future generations to
meet their needs. The basic definition of sustainable
construction was formulated in the conference organized by
CIB, held in the USA in 1994: its the creation and
management of the healthy environment in the construction
works and beyond their limits, following the principles of the
efficient consumption of resources and environmental
friendliness (Šaparauskas, 2001 etc.). This conception also
covers the sustainability-ensuring constructional materials,
safe construction practice and new technologies
Establishment of Healthy Working Environment at Liquefied Natural Gas Reservoir Park
No full textThe paper provides information on the use of liquefied natural gas and distribution in Europe and
worldwide. Paper has information displayed on the largest liquefied natural gas exporter and importing countries. View of liquefied natural gas transit, storage statistics and specific features in urope is provided. Has been studied accident statistics in the world linked with liquefied natural gas, as well as the analysis has been made of the most frequent causes of accidents.
During this research, calculations was carried out assessing the possible fire of liquefied natural gas (hereinafter LNG) in order to assess its consequences and prevalence, as well as assessing the potential impact of atmospheric in fire spread, also calculations were made to assess the blast wave spread. Other calculations were made in connection with LNG low temperatures and effects that could appear by inhaling evaporated LNG vapours. Research summarizes some of the most important occupational health and safety risks associated with the LNG storage, accidents and leak consequences, as well as offering some propositions of solving these problems
Work Anytime, Work Anywhere - SMART Work for Economic Growth and Regional Development
No full textAn increasing share of businesses and other organizations are keen to use smart work (distant work, telework); it has become a wide-spread practice that allows employees and their tasks to be distributed across settings away from a physical business location (i.e. a central office). New ICT solutions, rapidly developing technologies, as well as managerial changes can facilitate an increasing proportion of teleworkers. Smart work itself is being identified with an increase in productivity and satisfaction of the employees. It also gives an opportunity to digitally participate from distant locations, including the countryside, in the knowledge economy.
The purpose of this research is to identify the actual and potential use of telework in order to promote regional development. The principal results are as follows. In order to promote regional development using telework, numerous EU member states have created smart work centers in rural territories, e.g. resource centers in France, work hubs in Great Britain and telehouses in Hungary. The results of the questionnaire of inhabitants in two rural municipalities confirm that there is a potential for the use of telework also in Latvia. At the same time, most of the respondents seem to be overly skeptical about the use of telework to perform their professional duties; therefore additional activities for the promotion of telework should be made.
The semi-structured interviews with teleworkers and the owners of the co-working space Birojnica in Latvia show a more detailed picture of the daily life of a teleworkers. Teleworkers feel more independent, creative and productive. The main drawbacks are the loss of communication and control and the decrease in socialization. Most of the respondents see a potential in establishing smart work centers in the largest towns (especially towns with universities and vocational schools) and to some extent – also in rural territories. A promising solution seems to be the creation of smart work possibilities in and around already existing business support infrastructure, e.g. business incubators.
To conclude, smart work brings sustainable innovation in labor management of the 21st century. It provides positive effects on productivity, maintains a good work life balance, reduces commuting/travel time and the carbon footprint. Moreover, it can sustain the rural populations and thus counterbalance the concentration of the economic activity in metropolitan areas. However, further research is required in order to offer sustainable solutions for the telework outside metropolitan areas
Piemiņas dārzu veidošanas tradīcijas
No full textIkvienas tautas vēsturē ir ierakstīti nozīmīgi un liktenīgi brīži, kas iegūluši dziļi tautas atmiņā. Atceres brīžos nepieciešams rast mierinājumu un spēku. Cilvēkā dziļu emocionālu pārdzīvojumu izraisa daba un skaistums. Seno Austrumu zemju dārzu mākslu raksturoja dabas mīlestība un ar reliģiju saistīts simbolisms. Rietumeiropā parku veidoja saskaņā ar apkārtnes ainavu, apvienojot dabisko un mākslīgi radīto. Parkiem skaistumu piešķīra skuju un lapu koku veidotie kontrasti. Krievijā idealizētā parku ainava atgādināja gleznu. Latvijas teritorijā 18. gadsimtā iekopa sentimentālos un romantiskos dārzus. „Dvēseļu dārzs” Likteņupes Daugavas Krievkalna salā apmeklētājos izraisīs dziļu emocionālu pārdzīvojumu
The Benefits of Green Roofing for Latvian Building Environment
No full textGreen roofs serve several purposes for a building, such as absorbing rainwater, providing insulation, creating a habitat for wildlife and helping to lower urban air temperatures and mitigate the heat island effect. The modern trend started when green roofs were developed in Germany in the 1960s, and has since spread to many countries. Today, it is estimated that about 10% of all German roofs have been “greened”. Green roofs are also becoming increasingly popular in the United States, although they are not as common as in Europe; however, one sees more and more architects opting for green roofs as an alternative to large flat roofs. Green or vegetated roof is not so traditional roof type for Latvian building environment. Mainly because of a lot of the ideas that it harms all structure, problems with leaking, problems with hydro isolation, too large weight and a lot of additional maintenance works and costs. And the greatest idea is that this roof type is totally unsuitable for local weather conditions when historically green roofs are widely used in Norway and also in Great Britain where weather conditions are much more harmful for greenery. These ideas mainly are coming from the fear to get into the situation with high risk to maintain the building with green roof and if that is cost approved. In present research is given review on green roofing worldwide and Latvia, different roof systems and described the benefits of green roof implementation
Tēlotāja ģeometrija : mācību līdzeklis arhitektūras studentiem
No full textMācību līdzeklis ir paredzēts mācību priekšmeta "Tēlotāja ģeometrija" apguvei RTU studiju programmu ietvaros un tas satur teorētisku materiālu un praktiskus piemērus telpisku objektu attēlošanai divās dimensijā un pozicionālu un metrisku uzdevumu risināšanai ar tiem. Otrā daļā aplūkoti perspektīvas, ēnu teorijas un kotēto projekciju teorētiskie un praktiskie jautājumi. Pamatā grāmata paredzēta Arhitektūras fakultātes studentiem