Mechanism of P-n Junction Formation in Intrinsic Semiconductor by Laser Radiation
- Publication date
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- RTU
Abstract
I. 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